/*-------------------------------------------------------------------------
 *
 * nodeAgg.c
 *	  Routines to handle aggregate nodes.
 *
 *	  ExecAgg normally evaluates each aggregate in the following steps:
 *
 *		 transvalue = initcond
 *		 foreach input_tuple do
 *			transvalue = transfunc(transvalue, input_value(s))
 *		 result = finalfunc(transvalue, direct_argument(s))
 *
 *	  If a finalfunc is not supplied then the result is just the ending
 *	  value of transvalue.
 *
 *	  Other behaviors can be selected by the "aggsplit" mode, which exists
 *	  to support partial aggregation.  It is possible to:
 *	  * Skip running the finalfunc, so that the output is always the
 *	  final transvalue state.
 *	  * Substitute the combinefunc for the transfunc, so that transvalue
 *	  states (propagated up from a child partial-aggregation step) are merged
 *	  rather than processing raw input rows.  (The statements below about
 *	  the transfunc apply equally to the combinefunc, when it's selected.)
 *	  * Apply the serializefunc to the output values (this only makes sense
 *	  when skipping the finalfunc, since the serializefunc works on the
 *	  transvalue data type).
 *	  * Apply the deserializefunc to the input values (this only makes sense
 *	  when using the combinefunc, for similar reasons).
 *	  It is the planner's responsibility to connect up Agg nodes using these
 *	  alternate behaviors in a way that makes sense, with partial aggregation
 *	  results being fed to nodes that expect them.
 *
 *	  If a normal aggregate call specifies DISTINCT or ORDER BY, we sort the
 *	  input tuples and eliminate duplicates (if required) before performing
 *	  the above-depicted process.  (However, we don't do that for ordered-set
 *	  aggregates; their "ORDER BY" inputs are ordinary aggregate arguments
 *	  so far as this module is concerned.)	Note that partial aggregation
 *	  is not supported in these cases, since we couldn't ensure global
 *	  ordering or distinctness of the inputs.
 *
 *	  If transfunc is marked "strict" in pg_proc and initcond is NULL,
 *	  then the first non-NULL input_value is assigned directly to transvalue,
 *	  and transfunc isn't applied until the second non-NULL input_value.
 *	  The agg's first input type and transtype must be the same in this case!
 *
 *	  If transfunc is marked "strict" then NULL input_values are skipped,
 *	  keeping the previous transvalue.  If transfunc is not strict then it
 *	  is called for every input tuple and must deal with NULL initcond
 *	  or NULL input_values for itself.
 *
 *	  If finalfunc is marked "strict" then it is not called when the
 *	  ending transvalue is NULL, instead a NULL result is created
 *	  automatically (this is just the usual handling of strict functions,
 *	  of course).  A non-strict finalfunc can make its own choice of
 *	  what to return for a NULL ending transvalue.
 *
 *	  Ordered-set aggregates are treated specially in one other way: we
 *	  evaluate any "direct" arguments and pass them to the finalfunc along
 *	  with the transition value.
 *
 *	  A finalfunc can have additional arguments beyond the transvalue and
 *	  any "direct" arguments, corresponding to the input arguments of the
 *	  aggregate.  These are always just passed as NULL.  Such arguments may be
 *	  needed to allow resolution of a polymorphic aggregate's result type.
 *
 *	  We compute aggregate input expressions and run the transition functions
 *	  in a temporary econtext (aggstate->tmpcontext).  This is reset at least
 *	  once per input tuple, so when the transvalue datatype is
 *	  pass-by-reference, we have to be careful to copy it into a longer-lived
 *	  memory context, and free the prior value to avoid memory leakage.  We
 *	  store transvalues in another set of econtexts, aggstate->aggcontexts
 *	  (one per grouping set, see below), which are also used for the hashtable
 *	  structures in AGG_HASHED mode.  These econtexts are rescanned, not just
 *	  reset, at group boundaries so that aggregate transition functions can
 *	  register shutdown callbacks via AggRegisterCallback.
 *
 *	  The node's regular econtext (aggstate->ss.ps.ps_ExprContext) is used to
 *	  run finalize functions and compute the output tuple; this context can be
 *	  reset once per output tuple.
 *
 *	  The executor's AggState node is passed as the fmgr "context" value in
 *	  all transfunc and finalfunc calls.  It is not recommended that the
 *	  transition functions look at the AggState node directly, but they can
 *	  use AggCheckCallContext() to verify that they are being called by
 *	  nodeAgg.c (and not as ordinary SQL functions).  The main reason a
 *	  transition function might want to know this is so that it can avoid
 *	  palloc'ing a fixed-size pass-by-ref transition value on every call:
 *	  it can instead just scribble on and return its left input.  Ordinarily
 *	  it is completely forbidden for functions to modify pass-by-ref inputs,
 *	  but in the aggregate case we know the left input is either the initial
 *	  transition value or a previous function result, and in either case its
 *	  value need not be preserved.  See int8inc() for an example.  Notice that
 *	  advance_transition_function() is coded to avoid a data copy step when
 *	  the previous transition value pointer is returned.  Also, some
 *	  transition functions want to store working state in addition to the
 *	  nominal transition value; they can use the memory context returned by
 *	  AggCheckCallContext() to do that.
 *
 *	  Note: AggCheckCallContext() is available as of PostgreSQL 9.0.  The
 *	  AggState is available as context in earlier releases (back to 8.1),
 *	  but direct examination of the node is needed to use it before 9.0.
 *
 *	  As of 9.4, aggregate transition functions can also use AggGetAggref()
 *	  to get hold of the Aggref expression node for their aggregate call.
 *	  This is mainly intended for ordered-set aggregates, which are not
 *	  supported as window functions.  (A regular aggregate function would
 *	  need some fallback logic to use this, since there's no Aggref node
 *	  for a window function.)
 *
 *	  Grouping sets:
 *
 *	  A list of grouping sets which is structurally equivalent to a ROLLUP
 *	  clause (e.g. (a,b,c), (a,b), (a)) can be processed in a single pass over
 *	  ordered data.  We do this by keeping a separate set of transition values
 *	  for each grouping set being concurrently processed; for each input tuple
 *	  we update them all, and on group boundaries we reset those states
 *	  (starting at the front of the list) whose grouping values have changed
 *	  (the list of grouping sets is ordered from most specific to least
 *	  specific).
 *
 *	  Where more complex grouping sets are used, we break them down into
 *	  "phases", where each phase has a different sort order.  During each
 *	  phase but the last, the input tuples are additionally stored in a
 *	  tuplesort which is keyed to the next phase's sort order; during each
 *	  phase but the first, the input tuples are drawn from the previously
 *	  sorted data.  (The sorting of the data for the first phase is handled by
 *	  the planner, as it might be satisfied by underlying nodes.)
 *
 *	  From the perspective of aggregate transition and final functions, the
 *	  only issue regarding grouping sets is this: a single call site (flinfo)
 *	  of an aggregate function may be used for updating several different
 *	  transition values in turn. So the function must not cache in the flinfo
 *	  anything which logically belongs as part of the transition value (most
 *	  importantly, the memory context in which the transition value exists).
 *	  The support API functions (AggCheckCallContext, AggRegisterCallback) are
 *	  sensitive to the grouping set for which the aggregate function is
 *	  currently being called.
 *
 *	  TODO: AGG_HASHED doesn't support multiple grouping sets yet.
 *
 * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  src/backend/executor/nodeAgg.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/tlist.h"
#include "parser/parse_agg.h"
#include "parser/parse_coerce.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
#include "utils/tuplesort.h"
#include "utils/datum.h"


/*
 * AggStatePerTransData - per aggregate state value information
 *
 * Working state for updating the aggregate's state value, by calling the
 * transition function with an input row. This struct does not store the
 * information needed to produce the final aggregate result from the transition
 * state, that's stored in AggStatePerAggData instead. This separation allows
 * multiple aggregate results to be produced from a single state value.
 */
typedef struct AggStatePerTransData
{
	/*
	 * These values are set up during ExecInitAgg() and do not change
	 * thereafter:
	 */

	/*
	 * Link to an Aggref expr this state value is for.
	 *
	 * There can be multiple Aggref's sharing the same state value, as long as
	 * the inputs and transition function are identical. This points to the
	 * first one of them.
	 */
	Aggref	   *aggref;

	/*
	 * Nominal number of arguments for aggregate function.  For plain aggs,
	 * this excludes any ORDER BY expressions.  For ordered-set aggs, this
	 * counts both the direct and aggregated (ORDER BY) arguments.
	 */
	int			numArguments;

	/*
	 * Number of aggregated input columns.  This includes ORDER BY expressions
	 * in both the plain-agg and ordered-set cases.  Ordered-set direct args
	 * are not counted, though.
	 */
	int			numInputs;

	/*
	 * Number of aggregated input columns to pass to the transfn.  This
	 * includes the ORDER BY columns for ordered-set aggs, but not for plain
	 * aggs.  (This doesn't count the transition state value!)
	 */
	int			numTransInputs;

	/* Oid of the state transition or combine function */
	Oid			transfn_oid;

	/* Oid of the serialization function or InvalidOid */
	Oid			serialfn_oid;

	/* Oid of the deserialization function or InvalidOid */
	Oid			deserialfn_oid;

	/* Oid of state value's datatype */
	Oid			aggtranstype;

	/* ExprStates of the FILTER and argument expressions. */
	ExprState  *aggfilter;		/* state of FILTER expression, if any */
	List	   *args;			/* states of aggregated-argument expressions */
	List	   *aggdirectargs;	/* states of direct-argument expressions */

	/*
	 * fmgr lookup data for transition function or combine function.  Note in
	 * particular that the fn_strict flag is kept here.
	 */
	FmgrInfo	transfn;

	/* fmgr lookup data for serialization function */
	FmgrInfo	serialfn;

	/* fmgr lookup data for deserialization function */
	FmgrInfo	deserialfn;

	/* Input collation derived for aggregate */
	Oid			aggCollation;

	/* number of sorting columns */
	int			numSortCols;

	/* number of sorting columns to consider in DISTINCT comparisons */
	/* (this is either zero or the same as numSortCols) */
	int			numDistinctCols;

	/* deconstructed sorting information (arrays of length numSortCols) */
	AttrNumber *sortColIdx;
	Oid		   *sortOperators;
	Oid		   *sortCollations;
	bool	   *sortNullsFirst;

	/*
	 * fmgr lookup data for input columns' equality operators --- only
	 * set/used when aggregate has DISTINCT flag.  Note that these are in
	 * order of sort column index, not parameter index.
	 */
	FmgrInfo   *equalfns;		/* array of length numDistinctCols */

	/*
	 * initial value from pg_aggregate entry
	 */
	Datum		initValue;
	bool		initValueIsNull;

	/*
	 * We need the len and byval info for the agg's input and transition data
	 * types in order to know how to copy/delete values.
	 *
	 * Note that the info for the input type is used only when handling
	 * DISTINCT aggs with just one argument, so there is only one input type.
	 */
	int16		inputtypeLen,
				transtypeLen;
	bool		inputtypeByVal,
				transtypeByVal;

	/*
	 * Stuff for evaluation of inputs.  We used to just use ExecEvalExpr, but
	 * with the addition of ORDER BY we now need at least a slot for passing
	 * data to the sort object, which requires a tupledesc, so we might as
	 * well go whole hog and use ExecProject too.
	 */
	TupleDesc	evaldesc;		/* descriptor of input tuples */
	ProjectionInfo *evalproj;	/* projection machinery */

	/*
	 * Slots for holding the evaluated input arguments.  These are set up
	 * during ExecInitAgg() and then used for each input row.
	 */
	TupleTableSlot *evalslot;	/* current input tuple */
	TupleTableSlot *uniqslot;	/* used for multi-column DISTINCT */

	/*
	 * These values are working state that is initialized at the start of an
	 * input tuple group and updated for each input tuple.
	 *
	 * For a simple (non DISTINCT/ORDER BY) aggregate, we just feed the input
	 * values straight to the transition function.  If it's DISTINCT or
	 * requires ORDER BY, we pass the input values into a Tuplesort object;
	 * then at completion of the input tuple group, we scan the sorted values,
	 * eliminate duplicates if needed, and run the transition function on the
	 * rest.
	 *
	 * We need a separate tuplesort for each grouping set.
	 */

	Tuplesortstate **sortstates;	/* sort objects, if DISTINCT or ORDER BY */

	/*
	 * This field is a pre-initialized FunctionCallInfo struct used for
	 * calling this aggregate's transfn.  We save a few cycles per row by not
	 * re-initializing the unchanging fields; which isn't much, but it seems
	 * worth the extra space consumption.
	 */
	FunctionCallInfoData transfn_fcinfo;

	/* Likewise for serialization and deserialization functions */
	FunctionCallInfoData serialfn_fcinfo;

	FunctionCallInfoData deserialfn_fcinfo;
}	AggStatePerTransData;

/*
 * AggStatePerAggData - per-aggregate information
 *
 * This contains the information needed to call the final function, to produce
 * a final aggregate result from the state value. If there are multiple
 * identical Aggrefs in the query, they can all share the same per-agg data.
 *
 * These values are set up during ExecInitAgg() and do not change thereafter.
 */
typedef struct AggStatePerAggData
{
	/*
	 * Link to an Aggref expr this state value is for.
	 *
	 * There can be multiple identical Aggref's sharing the same per-agg. This
	 * points to the first one of them.
	 */
	Aggref	   *aggref;

	/* index to the state value which this agg should use */
	int			transno;

	/* Optional Oid of final function (may be InvalidOid) */
	Oid			finalfn_oid;

	/*
	 * fmgr lookup data for final function --- only valid when finalfn_oid oid
	 * is not InvalidOid.
	 */
	FmgrInfo	finalfn;

	/*
	 * Number of arguments to pass to the finalfn.  This is always at least 1
	 * (the transition state value) plus any ordered-set direct args. If the
	 * finalfn wants extra args then we pass nulls corresponding to the
	 * aggregated input columns.
	 */
	int			numFinalArgs;

	/*
	 * We need the len and byval info for the agg's result data type in order
	 * to know how to copy/delete values.
	 */
	int16		resulttypeLen;
	bool		resulttypeByVal;

}	AggStatePerAggData;

/*
 * AggStatePerGroupData - per-aggregate-per-group working state
 *
 * These values are working state that is initialized at the start of
 * an input tuple group and updated for each input tuple.
 *
 * In AGG_PLAIN and AGG_SORTED modes, we have a single array of these
 * structs (pointed to by aggstate->pergroup); we re-use the array for
 * each input group, if it's AGG_SORTED mode.  In AGG_HASHED mode, the
 * hash table contains an array of these structs for each tuple group.
 *
 * Logically, the sortstate field belongs in this struct, but we do not
 * keep it here for space reasons: we don't support DISTINCT aggregates
 * in AGG_HASHED mode, so there's no reason to use up a pointer field
 * in every entry of the hashtable.
 */
typedef struct AggStatePerGroupData
{
	Datum		transValue;		/* current transition value */
	bool		transValueIsNull;

	bool		noTransValue;	/* true if transValue not set yet */

	/*
	 * Note: noTransValue initially has the same value as transValueIsNull,
	 * and if true both are cleared to false at the same time.  They are not
	 * the same though: if transfn later returns a NULL, we want to keep that
	 * NULL and not auto-replace it with a later input value. Only the first
	 * non-NULL input will be auto-substituted.
	 */
} AggStatePerGroupData;

/*
 * AggStatePerPhaseData - per-grouping-set-phase state
 *
 * Grouping sets are divided into "phases", where a single phase can be
 * processed in one pass over the input. If there is more than one phase, then
 * at the end of input from the current phase, state is reset and another pass
 * taken over the data which has been re-sorted in the mean time.
 *
 * Accordingly, each phase specifies a list of grouping sets and group clause
 * information, plus each phase after the first also has a sort order.
 */
typedef struct AggStatePerPhaseData
{
	int			numsets;		/* number of grouping sets (or 0) */
	int		   *gset_lengths;	/* lengths of grouping sets */
	Bitmapset **grouped_cols;	/* column groupings for rollup */
	FmgrInfo   *eqfunctions;	/* per-grouping-field equality fns */
	Agg		   *aggnode;		/* Agg node for phase data */
	Sort	   *sortnode;		/* Sort node for input ordering for phase */
}	AggStatePerPhaseData;

/*
 * To implement hashed aggregation, we need a hashtable that stores a
 * representative tuple and an array of AggStatePerGroup structs for each
 * distinct set of GROUP BY column values.  We compute the hash key from
 * the GROUP BY columns.
 */
typedef struct AggHashEntryData *AggHashEntry;

typedef struct AggHashEntryData
{
	TupleHashEntryData shared;	/* common header for hash table entries */
	/* per-aggregate transition status array */
	AggStatePerGroupData pergroup[FLEXIBLE_ARRAY_MEMBER];
}	AggHashEntryData;

static void initialize_phase(AggState *aggstate, int newphase);
static TupleTableSlot *fetch_input_tuple(AggState *aggstate);
static void initialize_aggregates(AggState *aggstate,
					  AggStatePerGroup pergroup,
					  int numReset);
static void advance_transition_function(AggState *aggstate,
							AggStatePerTrans pertrans,
							AggStatePerGroup pergroupstate);
static void advance_aggregates(AggState *aggstate, AggStatePerGroup pergroup);
static void advance_combine_function(AggState *aggstate,
						 AggStatePerTrans pertrans,
						 AggStatePerGroup pergroupstate);
static void combine_aggregates(AggState *aggstate, AggStatePerGroup pergroup);
static void process_ordered_aggregate_single(AggState *aggstate,
								 AggStatePerTrans pertrans,
								 AggStatePerGroup pergroupstate);
static void process_ordered_aggregate_multi(AggState *aggstate,
								AggStatePerTrans pertrans,
								AggStatePerGroup pergroupstate);
static void finalize_aggregate(AggState *aggstate,
				   AggStatePerAgg peragg,
				   AggStatePerGroup pergroupstate,
				   Datum *resultVal, bool *resultIsNull);
static void finalize_partialaggregate(AggState *aggstate,
						  AggStatePerAgg peragg,
						  AggStatePerGroup pergroupstate,
						  Datum *resultVal, bool *resultIsNull);
static void prepare_projection_slot(AggState *aggstate,
						TupleTableSlot *slot,
						int currentSet);
static void finalize_aggregates(AggState *aggstate,
					AggStatePerAgg peragg,
					AggStatePerGroup pergroup,
					int currentSet);
static TupleTableSlot *project_aggregates(AggState *aggstate);
static Bitmapset *find_unaggregated_cols(AggState *aggstate);
static bool find_unaggregated_cols_walker(Node *node, Bitmapset **colnos);
static void build_hash_table(AggState *aggstate);
static AggHashEntry lookup_hash_entry(AggState *aggstate,
				  TupleTableSlot *inputslot);
static TupleTableSlot *agg_retrieve_direct(AggState *aggstate);
static void agg_fill_hash_table(AggState *aggstate);
static TupleTableSlot *agg_retrieve_hash_table(AggState *aggstate);
static Datum GetAggInitVal(Datum textInitVal, Oid transtype);
static void build_pertrans_for_aggref(AggStatePerTrans pertrans,
						  AggState *aggsate, EState *estate,
						  Aggref *aggref, Oid aggtransfn, Oid aggtranstype,
						  Oid aggserialfn, Oid aggdeserialfn,
						  Datum initValue, bool initValueIsNull,
						  Oid *inputTypes, int numArguments);
static int find_compatible_peragg(Aggref *newagg, AggState *aggstate,
					   int lastaggno, List **same_input_transnos);
static int find_compatible_pertrans(AggState *aggstate, Aggref *newagg,
						 Oid aggtransfn, Oid aggtranstype,
						 Oid aggserialfn, Oid aggdeserialfn,
						 Datum initValue, bool initValueIsNull,
						 List *transnos);


/*
 * Switch to phase "newphase", which must either be 0 (to reset) or
 * current_phase + 1. Juggle the tuplesorts accordingly.
 */
static void
initialize_phase(AggState *aggstate, int newphase)
{
	Assert(newphase == 0 || newphase == aggstate->current_phase + 1);

	/*
	 * Whatever the previous state, we're now done with whatever input
	 * tuplesort was in use.
	 */
	if (aggstate->sort_in)
	{
		tuplesort_end(aggstate->sort_in);
		aggstate->sort_in = NULL;
	}

	if (newphase == 0)
	{
		/*
		 * Discard any existing output tuplesort.
		 */
		if (aggstate->sort_out)
		{
			tuplesort_end(aggstate->sort_out);
			aggstate->sort_out = NULL;
		}
	}
	else
	{
		/*
		 * The old output tuplesort becomes the new input one, and this is the
		 * right time to actually sort it.
		 */
		aggstate->sort_in = aggstate->sort_out;
		aggstate->sort_out = NULL;
		Assert(aggstate->sort_in);
		tuplesort_performsort(aggstate->sort_in);
	}

	/*
	 * If this isn't the last phase, we need to sort appropriately for the
	 * next phase in sequence.
	 */
	if (newphase < aggstate->numphases - 1)
	{
		Sort	   *sortnode = aggstate->phases[newphase + 1].sortnode;
		PlanState  *outerNode = outerPlanState(aggstate);
		TupleDesc	tupDesc = ExecGetResultType(outerNode);

		aggstate->sort_out = tuplesort_begin_heap(tupDesc,
												  sortnode->numCols,
												  sortnode->sortColIdx,
												  sortnode->sortOperators,
												  sortnode->collations,
												  sortnode->nullsFirst,
												  work_mem,
												  false);
	}

	aggstate->current_phase = newphase;
	aggstate->phase = &aggstate->phases[newphase];
}

/*
 * Fetch a tuple from either the outer plan (for phase 0) or from the sorter
 * populated by the previous phase.  Copy it to the sorter for the next phase
 * if any.
 */
static TupleTableSlot *
fetch_input_tuple(AggState *aggstate)
{
	TupleTableSlot *slot;

	if (aggstate->sort_in)
	{
		if (!tuplesort_gettupleslot(aggstate->sort_in, true, aggstate->sort_slot,
									NULL))
			return NULL;
		slot = aggstate->sort_slot;
	}
	else
		slot = ExecProcNode(outerPlanState(aggstate));

	if (!TupIsNull(slot) && aggstate->sort_out)
		tuplesort_puttupleslot(aggstate->sort_out, slot);

	return slot;
}

/*
 * (Re)Initialize an individual aggregate.
 *
 * This function handles only one grouping set (already set in
 * aggstate->current_set).
 *
 * When called, CurrentMemoryContext should be the per-query context.
 */
static void
initialize_aggregate(AggState *aggstate, AggStatePerTrans pertrans,
					 AggStatePerGroup pergroupstate)
{
	/*
	 * Start a fresh sort operation for each DISTINCT/ORDER BY aggregate.
	 */
	if (pertrans->numSortCols > 0)
	{
		/*
		 * In case of rescan, maybe there could be an uncompleted sort
		 * operation?  Clean it up if so.
		 */
		if (pertrans->sortstates[aggstate->current_set])
			tuplesort_end(pertrans->sortstates[aggstate->current_set]);


		/*
		 * We use a plain Datum sorter when there's a single input column;
		 * otherwise sort the full tuple.  (See comments for
		 * process_ordered_aggregate_single.)
		 */
		if (pertrans->numInputs == 1)
			pertrans->sortstates[aggstate->current_set] =
				tuplesort_begin_datum(pertrans->evaldesc->attrs[0]->atttypid,
									  pertrans->sortOperators[0],
									  pertrans->sortCollations[0],
									  pertrans->sortNullsFirst[0],
									  work_mem, false);
		else
			pertrans->sortstates[aggstate->current_set] =
				tuplesort_begin_heap(pertrans->evaldesc,
									 pertrans->numSortCols,
									 pertrans->sortColIdx,
									 pertrans->sortOperators,
									 pertrans->sortCollations,
									 pertrans->sortNullsFirst,
									 work_mem, false);
	}

	/*
	 * (Re)set transValue to the initial value.
	 *
	 * Note that when the initial value is pass-by-ref, we must copy it (into
	 * the aggcontext) since we will pfree the transValue later.
	 */
	if (pertrans->initValueIsNull)
		pergroupstate->transValue = pertrans->initValue;
	else
	{
		MemoryContext oldContext;

		oldContext = MemoryContextSwitchTo(
		aggstate->aggcontexts[aggstate->current_set]->ecxt_per_tuple_memory);
		pergroupstate->transValue = datumCopy(pertrans->initValue,
											  pertrans->transtypeByVal,
											  pertrans->transtypeLen);
		MemoryContextSwitchTo(oldContext);
	}
	pergroupstate->transValueIsNull = pertrans->initValueIsNull;

	/*
	 * If the initial value for the transition state doesn't exist in the
	 * pg_aggregate table then we will let the first non-NULL value returned
	 * from the outer procNode become the initial value. (This is useful for
	 * aggregates like max() and min().) The noTransValue flag signals that we
	 * still need to do this.
	 */
	pergroupstate->noTransValue = pertrans->initValueIsNull;
}

/*
 * Initialize all aggregate transition states for a new group of input values.
 *
 * If there are multiple grouping sets, we initialize only the first numReset
 * of them (the grouping sets are ordered so that the most specific one, which
 * is reset most often, is first). As a convenience, if numReset is < 1, we
 * reinitialize all sets.
 *
 * When called, CurrentMemoryContext should be the per-query context.
 */
static void
initialize_aggregates(AggState *aggstate,
					  AggStatePerGroup pergroup,
					  int numReset)
{
	int			transno;
	int			numGroupingSets = Max(aggstate->phase->numsets, 1);
	int			setno = 0;
	AggStatePerTrans transstates = aggstate->pertrans;

	if (numReset < 1)
		numReset = numGroupingSets;

	for (transno = 0; transno < aggstate->numtrans; transno++)
	{
		AggStatePerTrans pertrans = &transstates[transno];

		for (setno = 0; setno < numReset; setno++)
		{
			AggStatePerGroup pergroupstate;

			pergroupstate = &pergroup[transno + (setno * (aggstate->numtrans))];

			aggstate->current_set = setno;

			initialize_aggregate(aggstate, pertrans, pergroupstate);
		}
	}
}

/*
 * Given new input value(s), advance the transition function of one aggregate
 * state within one grouping set only (already set in aggstate->current_set)
 *
 * The new values (and null flags) have been preloaded into argument positions
 * 1 and up in pertrans->transfn_fcinfo, so that we needn't copy them again to
 * pass to the transition function.  We also expect that the static fields of
 * the fcinfo are already initialized; that was done by ExecInitAgg().
 *
 * It doesn't matter which memory context this is called in.
 */
static void
advance_transition_function(AggState *aggstate,
							AggStatePerTrans pertrans,
							AggStatePerGroup pergroupstate)
{
	FunctionCallInfo fcinfo = &pertrans->transfn_fcinfo;
	MemoryContext oldContext;
	Datum		newVal;

	if (pertrans->transfn.fn_strict)
	{
		/*
		 * For a strict transfn, nothing happens when there's a NULL input; we
		 * just keep the prior transValue.
		 */
		int			numTransInputs = pertrans->numTransInputs;
		int			i;

		for (i = 1; i <= numTransInputs; i++)
		{
			if (fcinfo->argnull[i])
				return;
		}
		if (pergroupstate->noTransValue)
		{
			/*
			 * transValue has not been initialized. This is the first non-NULL
			 * input value. We use it as the initial value for transValue. (We
			 * already checked that the agg's input type is binary-compatible
			 * with its transtype, so straight copy here is OK.)
			 *
			 * We must copy the datum into aggcontext if it is pass-by-ref. We
			 * do not need to pfree the old transValue, since it's NULL.
			 */
			oldContext = MemoryContextSwitchTo(
											   aggstate->aggcontexts[aggstate->current_set]->ecxt_per_tuple_memory);
			pergroupstate->transValue = datumCopy(fcinfo->arg[1],
												  pertrans->transtypeByVal,
												  pertrans->transtypeLen);
			pergroupstate->transValueIsNull = false;
			pergroupstate->noTransValue = false;
			MemoryContextSwitchTo(oldContext);
			return;
		}
		if (pergroupstate->transValueIsNull)
		{
			/*
			 * Don't call a strict function with NULL inputs.  Note it is
			 * possible to get here despite the above tests, if the transfn is
			 * strict *and* returned a NULL on a prior cycle. If that happens
			 * we will propagate the NULL all the way to the end.
			 */
			return;
		}
	}

	/* We run the transition functions in per-input-tuple memory context */
	oldContext = MemoryContextSwitchTo(aggstate->tmpcontext->ecxt_per_tuple_memory);

	/* set up aggstate->curpertrans for AggGetAggref() */
	aggstate->curpertrans = pertrans;

	/*
	 * OK to call the transition function
	 */
	fcinfo->arg[0] = pergroupstate->transValue;
	fcinfo->argnull[0] = pergroupstate->transValueIsNull;
	fcinfo->isnull = false;		/* just in case transfn doesn't set it */

	newVal = FunctionCallInvoke(fcinfo);

	aggstate->curpertrans = NULL;

	/*
	 * If pass-by-ref datatype, must copy the new value into aggcontext and
	 * pfree the prior transValue.  But if transfn returned a pointer to its
	 * first input, we don't need to do anything.
	 */
	if (!pertrans->transtypeByVal &&
		DatumGetPointer(newVal) != DatumGetPointer(pergroupstate->transValue))
	{
		if (!fcinfo->isnull)
		{
			MemoryContextSwitchTo(aggstate->aggcontexts[aggstate->current_set]->ecxt_per_tuple_memory);
			newVal = datumCopy(newVal,
							   pertrans->transtypeByVal,
							   pertrans->transtypeLen);
		}
		if (!pergroupstate->transValueIsNull)
			pfree(DatumGetPointer(pergroupstate->transValue));
	}

	pergroupstate->transValue = newVal;
	pergroupstate->transValueIsNull = fcinfo->isnull;

	MemoryContextSwitchTo(oldContext);
}

/*
 * Advance each aggregate transition state for one input tuple.  The input
 * tuple has been stored in tmpcontext->ecxt_outertuple, so that it is
 * accessible to ExecEvalExpr.  pergroup is the array of per-group structs to
 * use (this might be in a hashtable entry).
 *
 * When called, CurrentMemoryContext should be the per-query context.
 */
static void
advance_aggregates(AggState *aggstate, AggStatePerGroup pergroup)
{
	int			transno;
	int			setno = 0;
	int			numGroupingSets = Max(aggstate->phase->numsets, 1);
	int			numTrans = aggstate->numtrans;

	for (transno = 0; transno < numTrans; transno++)
	{
		AggStatePerTrans pertrans = &aggstate->pertrans[transno];
		ExprState  *filter = pertrans->aggfilter;
		int			numTransInputs = pertrans->numTransInputs;
		int			i;
		TupleTableSlot *slot;

		/* Skip anything FILTERed out */
		if (filter)
		{
			Datum		res;
			bool		isnull;

			res = ExecEvalExprSwitchContext(filter, aggstate->tmpcontext,
											&isnull, NULL);
			if (isnull || !DatumGetBool(res))
				continue;
		}

		/* Evaluate the current input expressions for this aggregate */
		slot = ExecProject(pertrans->evalproj, NULL);

		if (pertrans->numSortCols > 0)
		{
			/* DISTINCT and/or ORDER BY case */
			Assert(slot->tts_nvalid == pertrans->numInputs);

			/*
			 * If the transfn is strict, we want to check for nullity before
			 * storing the row in the sorter, to save space if there are a lot
			 * of nulls.  Note that we must only check numTransInputs columns,
			 * not numInputs, since nullity in columns used only for sorting
			 * is not relevant here.
			 */
			if (pertrans->transfn.fn_strict)
			{
				for (i = 0; i < numTransInputs; i++)
				{
					if (slot->tts_isnull[i])
						break;
				}
				if (i < numTransInputs)
					continue;
			}

			for (setno = 0; setno < numGroupingSets; setno++)
			{
				/* OK, put the tuple into the tuplesort object */
				if (pertrans->numInputs == 1)
					tuplesort_putdatum(pertrans->sortstates[setno],
									   slot->tts_values[0],
									   slot->tts_isnull[0]);
				else
					tuplesort_puttupleslot(pertrans->sortstates[setno], slot);
			}
		}
		else
		{
			/* We can apply the transition function immediately */
			FunctionCallInfo fcinfo = &pertrans->transfn_fcinfo;

			/* Load values into fcinfo */
			/* Start from 1, since the 0th arg will be the transition value */
			Assert(slot->tts_nvalid >= numTransInputs);
			for (i = 0; i < numTransInputs; i++)
			{
				fcinfo->arg[i + 1] = slot->tts_values[i];
				fcinfo->argnull[i + 1] = slot->tts_isnull[i];
			}

			for (setno = 0; setno < numGroupingSets; setno++)
			{
				AggStatePerGroup pergroupstate = &pergroup[transno + (setno * numTrans)];

				aggstate->current_set = setno;

				advance_transition_function(aggstate, pertrans, pergroupstate);
			}
		}
	}
}

/*
 * combine_aggregates replaces advance_aggregates in DO_AGGSPLIT_COMBINE
 * mode.  The principal difference is that here we may need to apply the
 * deserialization function before running the transfn (which, in this mode,
 * is actually the aggregate's combinefn).  Also, we know we don't need to
 * handle FILTER, DISTINCT, ORDER BY, or grouping sets.
 */
static void
combine_aggregates(AggState *aggstate, AggStatePerGroup pergroup)
{
	int			transno;
	int			numTrans = aggstate->numtrans;

	/* combine not supported with grouping sets */
	Assert(aggstate->phase->numsets == 0);

	for (transno = 0; transno < numTrans; transno++)
	{
		AggStatePerTrans pertrans = &aggstate->pertrans[transno];
		AggStatePerGroup pergroupstate = &pergroup[transno];
		TupleTableSlot *slot;
		FunctionCallInfo fcinfo = &pertrans->transfn_fcinfo;

		/* Evaluate the current input expressions for this aggregate */
		slot = ExecProject(pertrans->evalproj, NULL);
		Assert(slot->tts_nvalid >= 1);

		/*
		 * deserialfn_oid will be set if we must deserialize the input state
		 * before calling the combine function
		 */
		if (OidIsValid(pertrans->deserialfn_oid))
		{
			/* Don't call a strict deserialization function with NULL input */
			if (pertrans->deserialfn.fn_strict && slot->tts_isnull[0])
			{
				fcinfo->arg[1] = slot->tts_values[0];
				fcinfo->argnull[1] = slot->tts_isnull[0];
			}
			else
			{
				FunctionCallInfo dsinfo = &pertrans->deserialfn_fcinfo;
				MemoryContext oldContext;

				dsinfo->arg[0] = slot->tts_values[0];
				dsinfo->argnull[0] = slot->tts_isnull[0];
				/* Dummy second argument for type-safety reasons */
				dsinfo->arg[1] = PointerGetDatum(NULL);
				dsinfo->argnull[1] = false;

				/*
				 * We run the deserialization functions in per-input-tuple
				 * memory context.
				 */
				oldContext = MemoryContextSwitchTo(aggstate->tmpcontext->ecxt_per_tuple_memory);

				fcinfo->arg[1] = FunctionCallInvoke(dsinfo);
				fcinfo->argnull[1] = dsinfo->isnull;

				MemoryContextSwitchTo(oldContext);
			}
		}
		else
		{
			fcinfo->arg[1] = slot->tts_values[0];
			fcinfo->argnull[1] = slot->tts_isnull[0];
		}

		advance_combine_function(aggstate, pertrans, pergroupstate);
	}
}

/*
 * Perform combination of states between 2 aggregate states. Effectively this
 * 'adds' two states together by whichever logic is defined in the aggregate
 * function's combine function.
 *
 * Note that in this case transfn is set to the combination function. This
 * perhaps should be changed to avoid confusion, but one field is ok for now
 * as they'll never be needed at the same time.
 */
static void
advance_combine_function(AggState *aggstate,
						 AggStatePerTrans pertrans,
						 AggStatePerGroup pergroupstate)
{
	FunctionCallInfo fcinfo = &pertrans->transfn_fcinfo;
	MemoryContext oldContext;
	Datum		newVal;

	if (pertrans->transfn.fn_strict)
	{
		/* if we're asked to merge to a NULL state, then do nothing */
		if (fcinfo->argnull[1])
			return;

		if (pergroupstate->noTransValue)
		{
			/*
			 * transValue has not yet been initialized.  If pass-by-ref
			 * datatype we must copy the combining state value into
			 * aggcontext.
			 */
			if (!pertrans->transtypeByVal)
			{
				oldContext = MemoryContextSwitchTo(
												   aggstate->aggcontexts[aggstate->current_set]->ecxt_per_tuple_memory);
				pergroupstate->transValue = datumCopy(fcinfo->arg[1],
													pertrans->transtypeByVal,
													  pertrans->transtypeLen);
				MemoryContextSwitchTo(oldContext);
			}
			else
				pergroupstate->transValue = fcinfo->arg[1];

			pergroupstate->transValueIsNull = false;
			pergroupstate->noTransValue = false;
			return;
		}
	}

	/* We run the combine functions in per-input-tuple memory context */
	oldContext = MemoryContextSwitchTo(aggstate->tmpcontext->ecxt_per_tuple_memory);

	/* set up aggstate->curpertrans for AggGetAggref() */
	aggstate->curpertrans = pertrans;

	/*
	 * OK to call the combine function
	 */
	fcinfo->arg[0] = pergroupstate->transValue;
	fcinfo->argnull[0] = pergroupstate->transValueIsNull;
	fcinfo->isnull = false;		/* just in case combine func doesn't set it */

	newVal = FunctionCallInvoke(fcinfo);

	aggstate->curpertrans = NULL;

	/*
	 * If pass-by-ref datatype, must copy the new value into aggcontext and
	 * pfree the prior transValue.  But if the combine function returned a
	 * pointer to its first input, we don't need to do anything.
	 */
	if (!pertrans->transtypeByVal &&
		DatumGetPointer(newVal) != DatumGetPointer(pergroupstate->transValue))
	{
		if (!fcinfo->isnull)
		{
			MemoryContextSwitchTo(aggstate->aggcontexts[aggstate->current_set]->ecxt_per_tuple_memory);
			newVal = datumCopy(newVal,
							   pertrans->transtypeByVal,
							   pertrans->transtypeLen);
		}
		if (!pergroupstate->transValueIsNull)
			pfree(DatumGetPointer(pergroupstate->transValue));
	}

	pergroupstate->transValue = newVal;
	pergroupstate->transValueIsNull = fcinfo->isnull;

	MemoryContextSwitchTo(oldContext);
}


/*
 * Run the transition function for a DISTINCT or ORDER BY aggregate
 * with only one input.  This is called after we have completed
 * entering all the input values into the sort object.  We complete the
 * sort, read out the values in sorted order, and run the transition
 * function on each value (applying DISTINCT if appropriate).
 *
 * Note that the strictness of the transition function was checked when
 * entering the values into the sort, so we don't check it again here;
 * we just apply standard SQL DISTINCT logic.
 *
 * The one-input case is handled separately from the multi-input case
 * for performance reasons: for single by-value inputs, such as the
 * common case of count(distinct id), the tuplesort_getdatum code path
 * is around 300% faster.  (The speedup for by-reference types is less
 * but still noticeable.)
 *
 * This function handles only one grouping set (already set in
 * aggstate->current_set).
 *
 * When called, CurrentMemoryContext should be the per-query context.
 */
static void
process_ordered_aggregate_single(AggState *aggstate,
								 AggStatePerTrans pertrans,
								 AggStatePerGroup pergroupstate)
{
	Datum		oldVal = (Datum) 0;
	bool		oldIsNull = true;
	bool		haveOldVal = false;
	MemoryContext workcontext = aggstate->tmpcontext->ecxt_per_tuple_memory;
	MemoryContext oldContext;
	bool		isDistinct = (pertrans->numDistinctCols > 0);
	Datum		newAbbrevVal = (Datum) 0;
	Datum		oldAbbrevVal = (Datum) 0;
	FunctionCallInfo fcinfo = &pertrans->transfn_fcinfo;
	Datum	   *newVal;
	bool	   *isNull;

	Assert(pertrans->numDistinctCols < 2);

	tuplesort_performsort(pertrans->sortstates[aggstate->current_set]);

	/* Load the column into argument 1 (arg 0 will be transition value) */
	newVal = fcinfo->arg + 1;
	isNull = fcinfo->argnull + 1;

	/*
	 * Note: if input type is pass-by-ref, the datums returned by the sort are
	 * freshly palloc'd in the per-query context, so we must be careful to
	 * pfree them when they are no longer needed.
	 */

	while (tuplesort_getdatum(pertrans->sortstates[aggstate->current_set],
							  true, newVal, isNull, &newAbbrevVal))
	{
		/*
		 * Clear and select the working context for evaluation of the equality
		 * function and transition function.
		 */
		MemoryContextReset(workcontext);
		oldContext = MemoryContextSwitchTo(workcontext);

		/*
		 * If DISTINCT mode, and not distinct from prior, skip it.
		 *
		 * Note: we assume equality functions don't care about collation.
		 */
		if (isDistinct &&
			haveOldVal &&
			((oldIsNull && *isNull) ||
			 (!oldIsNull && !*isNull &&
			  oldAbbrevVal == newAbbrevVal &&
			  DatumGetBool(FunctionCall2(&pertrans->equalfns[0],
										 oldVal, *newVal)))))
		{
			/* equal to prior, so forget this one */
			if (!pertrans->inputtypeByVal && !*isNull)
				pfree(DatumGetPointer(*newVal));
		}
		else
		{
			advance_transition_function(aggstate, pertrans, pergroupstate);
			/* forget the old value, if any */
			if (!oldIsNull && !pertrans->inputtypeByVal)
				pfree(DatumGetPointer(oldVal));
			/* and remember the new one for subsequent equality checks */
			oldVal = *newVal;
			oldAbbrevVal = newAbbrevVal;
			oldIsNull = *isNull;
			haveOldVal = true;
		}

		MemoryContextSwitchTo(oldContext);
	}

	if (!oldIsNull && !pertrans->inputtypeByVal)
		pfree(DatumGetPointer(oldVal));

	tuplesort_end(pertrans->sortstates[aggstate->current_set]);
	pertrans->sortstates[aggstate->current_set] = NULL;
}

/*
 * Run the transition function for a DISTINCT or ORDER BY aggregate
 * with more than one input.  This is called after we have completed
 * entering all the input values into the sort object.  We complete the
 * sort, read out the values in sorted order, and run the transition
 * function on each value (applying DISTINCT if appropriate).
 *
 * This function handles only one grouping set (already set in
 * aggstate->current_set).
 *
 * When called, CurrentMemoryContext should be the per-query context.
 */
static void
process_ordered_aggregate_multi(AggState *aggstate,
								AggStatePerTrans pertrans,
								AggStatePerGroup pergroupstate)
{
	MemoryContext workcontext = aggstate->tmpcontext->ecxt_per_tuple_memory;
	FunctionCallInfo fcinfo = &pertrans->transfn_fcinfo;
	TupleTableSlot *slot1 = pertrans->evalslot;
	TupleTableSlot *slot2 = pertrans->uniqslot;
	int			numTransInputs = pertrans->numTransInputs;
	int			numDistinctCols = pertrans->numDistinctCols;
	Datum		newAbbrevVal = (Datum) 0;
	Datum		oldAbbrevVal = (Datum) 0;
	bool		haveOldValue = false;
	int			i;

	tuplesort_performsort(pertrans->sortstates[aggstate->current_set]);

	ExecClearTuple(slot1);
	if (slot2)
		ExecClearTuple(slot2);

	while (tuplesort_gettupleslot(pertrans->sortstates[aggstate->current_set],
								  true, slot1, &newAbbrevVal))
	{
		/*
		 * Extract the first numTransInputs columns as datums to pass to the
		 * transfn.  (This will help execTuplesMatch too, so we do it
		 * immediately.)
		 */
		slot_getsomeattrs(slot1, numTransInputs);

		if (numDistinctCols == 0 ||
			!haveOldValue ||
			newAbbrevVal != oldAbbrevVal ||
			!execTuplesMatch(slot1, slot2,
							 numDistinctCols,
							 pertrans->sortColIdx,
							 pertrans->equalfns,
							 workcontext))
		{
			/* Load values into fcinfo */
			/* Start from 1, since the 0th arg will be the transition value */
			for (i = 0; i < numTransInputs; i++)
			{
				fcinfo->arg[i + 1] = slot1->tts_values[i];
				fcinfo->argnull[i + 1] = slot1->tts_isnull[i];
			}

			advance_transition_function(aggstate, pertrans, pergroupstate);

			if (numDistinctCols > 0)
			{
				/* swap the slot pointers to retain the current tuple */
				TupleTableSlot *tmpslot = slot2;

				slot2 = slot1;
				slot1 = tmpslot;
				/* avoid execTuplesMatch() calls by reusing abbreviated keys */
				oldAbbrevVal = newAbbrevVal;
				haveOldValue = true;
			}
		}

		/* Reset context each time, unless execTuplesMatch did it for us */
		if (numDistinctCols == 0)
			MemoryContextReset(workcontext);

		ExecClearTuple(slot1);
	}

	if (slot2)
		ExecClearTuple(slot2);

	tuplesort_end(pertrans->sortstates[aggstate->current_set]);
	pertrans->sortstates[aggstate->current_set] = NULL;
}

/*
 * Compute the final value of one aggregate.
 *
 * This function handles only one grouping set (already set in
 * aggstate->current_set).
 *
 * The finalfunction will be run, and the result delivered, in the
 * output-tuple context; caller's CurrentMemoryContext does not matter.
 *
 * The finalfn uses the state as set in the transno. This also might be
 * being used by another aggregate function, so it's important that we do
 * nothing destructive here.
 */
static void
finalize_aggregate(AggState *aggstate,
				   AggStatePerAgg peragg,
				   AggStatePerGroup pergroupstate,
				   Datum *resultVal, bool *resultIsNull)
{
	FunctionCallInfoData fcinfo;
	bool		anynull = false;
	MemoryContext oldContext;
	int			i;
	ListCell   *lc;
	AggStatePerTrans pertrans = &aggstate->pertrans[peragg->transno];

	oldContext = MemoryContextSwitchTo(aggstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory);

	/*
	 * Evaluate any direct arguments.  We do this even if there's no finalfn
	 * (which is unlikely anyway), so that side-effects happen as expected.
	 * The direct arguments go into arg positions 1 and up, leaving position 0
	 * for the transition state value.
	 */
	i = 1;
	foreach(lc, pertrans->aggdirectargs)
	{
		ExprState  *expr = (ExprState *) lfirst(lc);

		fcinfo.arg[i] = ExecEvalExpr(expr,
									 aggstate->ss.ps.ps_ExprContext,
									 &fcinfo.argnull[i],
									 NULL);
		anynull |= fcinfo.argnull[i];
		i++;
	}

	/*
	 * Apply the agg's finalfn if one is provided, else return transValue.
	 */
	if (OidIsValid(peragg->finalfn_oid))
	{
		int			numFinalArgs = peragg->numFinalArgs;

		/* set up aggstate->curpertrans for AggGetAggref() */
		aggstate->curpertrans = pertrans;

		InitFunctionCallInfoData(fcinfo, &peragg->finalfn,
								 numFinalArgs,
								 pertrans->aggCollation,
								 (void *) aggstate, NULL);

		/* Fill in the transition state value */
		fcinfo.arg[0] = pergroupstate->transValue;
		fcinfo.argnull[0] = pergroupstate->transValueIsNull;
		anynull |= pergroupstate->transValueIsNull;

		/* Fill any remaining argument positions with nulls */
		for (; i < numFinalArgs; i++)
		{
			fcinfo.arg[i] = (Datum) 0;
			fcinfo.argnull[i] = true;
			anynull = true;
		}

		if (fcinfo.flinfo->fn_strict && anynull)
		{
			/* don't call a strict function with NULL inputs */
			*resultVal = (Datum) 0;
			*resultIsNull = true;
		}
		else
		{
			*resultVal = FunctionCallInvoke(&fcinfo);
			*resultIsNull = fcinfo.isnull;
		}
		aggstate->curpertrans = NULL;
	}
	else
	{
		*resultVal = pergroupstate->transValue;
		*resultIsNull = pergroupstate->transValueIsNull;
	}

	/*
	 * If result is pass-by-ref, make sure it is in the right context.
	 */
	if (!peragg->resulttypeByVal && !*resultIsNull &&
		!MemoryContextContains(CurrentMemoryContext,
							   DatumGetPointer(*resultVal)))
		*resultVal = datumCopy(*resultVal,
							   peragg->resulttypeByVal,
							   peragg->resulttypeLen);

	MemoryContextSwitchTo(oldContext);
}

/*
 * Compute the output value of one partial aggregate.
 *
 * The serialization function will be run, and the result delivered, in the
 * output-tuple context; caller's CurrentMemoryContext does not matter.
 */
static void
finalize_partialaggregate(AggState *aggstate,
						  AggStatePerAgg peragg,
						  AggStatePerGroup pergroupstate,
						  Datum *resultVal, bool *resultIsNull)
{
	AggStatePerTrans pertrans = &aggstate->pertrans[peragg->transno];
	MemoryContext oldContext;

	oldContext = MemoryContextSwitchTo(aggstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory);

	/*
	 * serialfn_oid will be set if we must serialize the transvalue before
	 * returning it
	 */
	if (OidIsValid(pertrans->serialfn_oid))
	{
		/* Don't call a strict serialization function with NULL input. */
		if (pertrans->serialfn.fn_strict && pergroupstate->transValueIsNull)
		{
			*resultVal = (Datum) 0;
			*resultIsNull = true;
		}
		else
		{
			FunctionCallInfo fcinfo = &pertrans->serialfn_fcinfo;

			fcinfo->arg[0] = pergroupstate->transValue;
			fcinfo->argnull[0] = pergroupstate->transValueIsNull;

			*resultVal = FunctionCallInvoke(fcinfo);
			*resultIsNull = fcinfo->isnull;
		}
	}
	else
	{
		*resultVal = pergroupstate->transValue;
		*resultIsNull = pergroupstate->transValueIsNull;
	}

	/* If result is pass-by-ref, make sure it is in the right context. */
	if (!peragg->resulttypeByVal && !*resultIsNull &&
		!MemoryContextContains(CurrentMemoryContext,
							   DatumGetPointer(*resultVal)))
		*resultVal = datumCopy(*resultVal,
							   peragg->resulttypeByVal,
							   peragg->resulttypeLen);

	MemoryContextSwitchTo(oldContext);
}

/*
 * Prepare to finalize and project based on the specified representative tuple
 * slot and grouping set.
 *
 * In the specified tuple slot, force to null all attributes that should be
 * read as null in the context of the current grouping set.  Also stash the
 * current group bitmap where GroupingExpr can get at it.
 *
 * This relies on three conditions:
 *
 * 1) Nothing is ever going to try and extract the whole tuple from this slot,
 * only reference it in evaluations, which will only access individual
 * attributes.
 *
 * 2) No system columns are going to need to be nulled. (If a system column is
 * referenced in a group clause, it is actually projected in the outer plan
 * tlist.)
 *
 * 3) Within a given phase, we never need to recover the value of an attribute
 * once it has been set to null.
 *
 * Poking into the slot this way is a bit ugly, but the consensus is that the
 * alternative was worse.
 */
static void
prepare_projection_slot(AggState *aggstate, TupleTableSlot *slot, int currentSet)
{
	if (aggstate->phase->grouped_cols)
	{
		Bitmapset  *grouped_cols = aggstate->phase->grouped_cols[currentSet];

		aggstate->grouped_cols = grouped_cols;

		if (slot->tts_isempty)
		{
			/*
			 * Force all values to be NULL if working on an empty input tuple
			 * (i.e. an empty grouping set for which no input rows were
			 * supplied).
			 */
			ExecStoreAllNullTuple(slot);
		}
		else if (aggstate->all_grouped_cols)
		{
			ListCell   *lc;

			/* all_grouped_cols is arranged in desc order */
			slot_getsomeattrs(slot, linitial_int(aggstate->all_grouped_cols));

			foreach(lc, aggstate->all_grouped_cols)
			{
				int			attnum = lfirst_int(lc);

				if (!bms_is_member(attnum, grouped_cols))
					slot->tts_isnull[attnum - 1] = true;
			}
		}
	}
}

/*
 * Compute the final value of all aggregates for one group.
 *
 * This function handles only one grouping set at a time.
 *
 * Results are stored in the output econtext aggvalues/aggnulls.
 */
static void
finalize_aggregates(AggState *aggstate,
					AggStatePerAgg peraggs,
					AggStatePerGroup pergroup,
					int currentSet)
{
	ExprContext *econtext = aggstate->ss.ps.ps_ExprContext;
	Datum	   *aggvalues = econtext->ecxt_aggvalues;
	bool	   *aggnulls = econtext->ecxt_aggnulls;
	int			aggno;

	Assert(currentSet == 0 ||
		   ((Agg *) aggstate->ss.ps.plan)->aggstrategy != AGG_HASHED);

	aggstate->current_set = currentSet;

	for (aggno = 0; aggno < aggstate->numaggs; aggno++)
	{
		AggStatePerAgg peragg = &peraggs[aggno];
		int			transno = peragg->transno;
		AggStatePerTrans pertrans = &aggstate->pertrans[transno];
		AggStatePerGroup pergroupstate;

		pergroupstate = &pergroup[transno + (currentSet * (aggstate->numtrans))];

		if (pertrans->numSortCols > 0)
		{
			Assert(((Agg *) aggstate->ss.ps.plan)->aggstrategy != AGG_HASHED);

			if (pertrans->numInputs == 1)
				process_ordered_aggregate_single(aggstate,
												 pertrans,
												 pergroupstate);
			else
				process_ordered_aggregate_multi(aggstate,
												pertrans,
												pergroupstate);
		}

		if (DO_AGGSPLIT_SKIPFINAL(aggstate->aggsplit))
			finalize_partialaggregate(aggstate, peragg, pergroupstate,
									  &aggvalues[aggno], &aggnulls[aggno]);
		else
			finalize_aggregate(aggstate, peragg, pergroupstate,
							   &aggvalues[aggno], &aggnulls[aggno]);
	}
}

/*
 * Project the result of a group (whose aggs have already been calculated by
 * finalize_aggregates). Returns the result slot, or NULL if no row is
 * projected (suppressed by qual or by an empty SRF).
 */
static TupleTableSlot *
project_aggregates(AggState *aggstate)
{
	ExprContext *econtext = aggstate->ss.ps.ps_ExprContext;

	/*
	 * Check the qual (HAVING clause); if the group does not match, ignore it.
	 */
	if (ExecQual(aggstate->ss.ps.qual, econtext, false))
	{
		/*
		 * Form and return or store a projection tuple using the aggregate
		 * results and the representative input tuple.
		 */
		ExprDoneCond isDone;
		TupleTableSlot *result;

		result = ExecProject(aggstate->ss.ps.ps_ProjInfo, &isDone);

		if (isDone != ExprEndResult)
		{
			aggstate->ss.ps.ps_TupFromTlist =
				(isDone == ExprMultipleResult);
			return result;
		}
	}
	else
		InstrCountFiltered1(aggstate, 1);

	return NULL;
}

/*
 * find_unaggregated_cols
 *	  Construct a bitmapset of the column numbers of un-aggregated Vars
 *	  appearing in our targetlist and qual (HAVING clause)
 */
static Bitmapset *
find_unaggregated_cols(AggState *aggstate)
{
	Agg		   *node = (Agg *) aggstate->ss.ps.plan;
	Bitmapset  *colnos;

	colnos = NULL;
	(void) find_unaggregated_cols_walker((Node *) node->plan.targetlist,
										 &colnos);
	(void) find_unaggregated_cols_walker((Node *) node->plan.qual,
										 &colnos);
	return colnos;
}

static bool
find_unaggregated_cols_walker(Node *node, Bitmapset **colnos)
{
	if (node == NULL)
		return false;
	if (IsA(node, Var))
	{
		Var		   *var = (Var *) node;

		/* setrefs.c should have set the varno to OUTER_VAR */
		Assert(var->varno == OUTER_VAR);
		Assert(var->varlevelsup == 0);
		*colnos = bms_add_member(*colnos, var->varattno);
		return false;
	}
	if (IsA(node, Aggref) ||IsA(node, GroupingFunc))
	{
		/* do not descend into aggregate exprs */
		return false;
	}
	return expression_tree_walker(node, find_unaggregated_cols_walker,
								  (void *) colnos);
}

/*
 * Initialize the hash table to empty.
 *
 * The hash table always lives in the aggcontext memory context.
 */
static void
build_hash_table(AggState *aggstate)
{
	Agg		   *node = (Agg *) aggstate->ss.ps.plan;
	MemoryContext tmpmem = aggstate->tmpcontext->ecxt_per_tuple_memory;
	Size		entrysize;

	Assert(node->aggstrategy == AGG_HASHED);
	Assert(node->numGroups > 0);

	entrysize = offsetof(AggHashEntryData, pergroup) +
		aggstate->numaggs * sizeof(AggStatePerGroupData);

	aggstate->hashtable = BuildTupleHashTable(node->numCols,
											  node->grpColIdx,
											  aggstate->phase->eqfunctions,
											  aggstate->hashfunctions,
											  node->numGroups,
											  entrysize,
							 aggstate->aggcontexts[0]->ecxt_per_tuple_memory,
											  tmpmem);
}

/*
 * Create a list of the tuple columns that actually need to be stored in
 * hashtable entries.  The incoming tuples from the child plan node will
 * contain grouping columns, other columns referenced in our targetlist and
 * qual, columns used to compute the aggregate functions, and perhaps just
 * junk columns we don't use at all.  Only columns of the first two types
 * need to be stored in the hashtable, and getting rid of the others can
 * make the table entries significantly smaller.  To avoid messing up Var
 * numbering, we keep the same tuple descriptor for hashtable entries as the
 * incoming tuples have, but set unwanted columns to NULL in the tuples that
 * go into the table.
 *
 * To eliminate duplicates, we build a bitmapset of the needed columns, then
 * convert it to an integer list (cheaper to scan at runtime). The list is
 * in decreasing order so that the first entry is the largest;
 * lookup_hash_entry depends on this to use slot_getsomeattrs correctly.
 * Note that the list is preserved over ExecReScanAgg, so we allocate it in
 * the per-query context (unlike the hash table itself).
 *
 * Note: at present, searching the tlist/qual is not really necessary since
 * the parser should disallow any unaggregated references to ungrouped
 * columns.  However, the search will be needed when we add support for
 * SQL99 semantics that allow use of "functionally dependent" columns that
 * haven't been explicitly grouped by.
 */
static List *
find_hash_columns(AggState *aggstate)
{
	Agg		   *node = (Agg *) aggstate->ss.ps.plan;
	Bitmapset  *colnos;
	List	   *collist;
	int			i;

	/* Find Vars that will be needed in tlist and qual */
	colnos = find_unaggregated_cols(aggstate);
	/* Add in all the grouping columns */
	for (i = 0; i < node->numCols; i++)
		colnos = bms_add_member(colnos, node->grpColIdx[i]);
	/* Convert to list, using lcons so largest element ends up first */
	collist = NIL;
	while ((i = bms_first_member(colnos)) >= 0)
		collist = lcons_int(i, collist);
	bms_free(colnos);

	return collist;
}

/*
 * Estimate per-hash-table-entry overhead for the planner.
 *
 * Note that the estimate does not include space for pass-by-reference
 * transition data values, nor for the representative tuple of each group.
 */
Size
hash_agg_entry_size(int numAggs)
{
	Size		entrysize;

	/* This must match build_hash_table */
	entrysize = offsetof(AggHashEntryData, pergroup) +
		numAggs * sizeof(AggStatePerGroupData);
	entrysize = MAXALIGN(entrysize);
	/* Account for hashtable overhead (assuming fill factor = 1) */
	entrysize += 3 * sizeof(void *);
	return entrysize;
}

/*
 * Find or create a hashtable entry for the tuple group containing the
 * given tuple.
 *
 * When called, CurrentMemoryContext should be the per-query context.
 */
static AggHashEntry
lookup_hash_entry(AggState *aggstate, TupleTableSlot *inputslot)
{
	TupleTableSlot *hashslot = aggstate->hashslot;
	ListCell   *l;
	AggHashEntry entry;
	bool		isnew;

	/* if first time through, initialize hashslot by cloning input slot */
	if (hashslot->tts_tupleDescriptor == NULL)
	{
		ExecSetSlotDescriptor(hashslot, inputslot->tts_tupleDescriptor);
		/* Make sure all unused columns are NULLs */
		ExecStoreAllNullTuple(hashslot);
	}

	/* transfer just the needed columns into hashslot */
	slot_getsomeattrs(inputslot, linitial_int(aggstate->hash_needed));
	foreach(l, aggstate->hash_needed)
	{
		int			varNumber = lfirst_int(l) - 1;

		hashslot->tts_values[varNumber] = inputslot->tts_values[varNumber];
		hashslot->tts_isnull[varNumber] = inputslot->tts_isnull[varNumber];
	}

	/* find or create the hashtable entry using the filtered tuple */
	entry = (AggHashEntry) LookupTupleHashEntry(aggstate->hashtable,
												hashslot,
												&isnew);

	if (isnew)
	{
		/* initialize aggregates for new tuple group */
		initialize_aggregates(aggstate, entry->pergroup, 0);
	}

	return entry;
}

/*
 * ExecAgg -
 *
 *	  ExecAgg receives tuples from its outer subplan and aggregates over
 *	  the appropriate attribute for each aggregate function use (Aggref
 *	  node) appearing in the targetlist or qual of the node.  The number
 *	  of tuples to aggregate over depends on whether grouped or plain
 *	  aggregation is selected.  In grouped aggregation, we produce a result
 *	  row for each group; in plain aggregation there's a single result row
 *	  for the whole query.  In either case, the value of each aggregate is
 *	  stored in the expression context to be used when ExecProject evaluates
 *	  the result tuple.
 */
TupleTableSlot *
ExecAgg(AggState *node)
{
	TupleTableSlot *result;

	/*
	 * Check to see if we're still projecting out tuples from a previous agg
	 * tuple (because there is a function-returning-set in the projection
	 * expressions).  If so, try to project another one.
	 */
	if (node->ss.ps.ps_TupFromTlist)
	{
		ExprDoneCond isDone;

		result = ExecProject(node->ss.ps.ps_ProjInfo, &isDone);
		if (isDone == ExprMultipleResult)
			return result;
		/* Done with that source tuple... */
		node->ss.ps.ps_TupFromTlist = false;
	}

	/*
	 * (We must do the ps_TupFromTlist check first, because in some cases
	 * agg_done gets set before we emit the final aggregate tuple, and we have
	 * to finish running SRFs for it.)
	 */
	if (!node->agg_done)
	{
		/* Dispatch based on strategy */
		switch (node->phase->aggnode->aggstrategy)
		{
			case AGG_HASHED:
				if (!node->table_filled)
					agg_fill_hash_table(node);
				result = agg_retrieve_hash_table(node);
				break;
			default:
				result = agg_retrieve_direct(node);
				break;
		}

		if (!TupIsNull(result))
			return result;
	}

	return NULL;
}

/*
 * ExecAgg for non-hashed case
 */
static TupleTableSlot *
agg_retrieve_direct(AggState *aggstate)
{
	Agg		   *node = aggstate->phase->aggnode;
	ExprContext *econtext;
	ExprContext *tmpcontext;
	AggStatePerAgg peragg;
	AggStatePerGroup pergroup;
	TupleTableSlot *outerslot;
	TupleTableSlot *firstSlot;
	TupleTableSlot *result;
	bool		hasGroupingSets = aggstate->phase->numsets > 0;
	int			numGroupingSets = Max(aggstate->phase->numsets, 1);
	int			currentSet;
	int			nextSetSize;
	int			numReset;
	int			i;

	/*
	 * get state info from node
	 *
	 * econtext is the per-output-tuple expression context
	 *
	 * tmpcontext is the per-input-tuple expression context
	 */
	econtext = aggstate->ss.ps.ps_ExprContext;
	tmpcontext = aggstate->tmpcontext;

	peragg = aggstate->peragg;
	pergroup = aggstate->pergroup;
	firstSlot = aggstate->ss.ss_ScanTupleSlot;

	/*
	 * We loop retrieving groups until we find one matching
	 * aggstate->ss.ps.qual
	 *
	 * For grouping sets, we have the invariant that aggstate->projected_set
	 * is either -1 (initial call) or the index (starting from 0) in
	 * gset_lengths for the group we just completed (either by projecting a
	 * row or by discarding it in the qual).
	 */
	while (!aggstate->agg_done)
	{
		/*
		 * Clear the per-output-tuple context for each group, as well as
		 * aggcontext (which contains any pass-by-ref transvalues of the old
		 * group).  Some aggregate functions store working state in child
		 * contexts; those now get reset automatically without us needing to
		 * do anything special.
		 *
		 * We use ReScanExprContext not just ResetExprContext because we want
		 * any registered shutdown callbacks to be called.  That allows
		 * aggregate functions to ensure they've cleaned up any non-memory
		 * resources.
		 */
		ReScanExprContext(econtext);

		/*
		 * Determine how many grouping sets need to be reset at this boundary.
		 */
		if (aggstate->projected_set >= 0 &&
			aggstate->projected_set < numGroupingSets)
			numReset = aggstate->projected_set + 1;
		else
			numReset = numGroupingSets;

		/*
		 * numReset can change on a phase boundary, but that's OK; we want to
		 * reset the contexts used in _this_ phase, and later, after possibly
		 * changing phase, initialize the right number of aggregates for the
		 * _new_ phase.
		 */

		for (i = 0; i < numReset; i++)
		{
			ReScanExprContext(aggstate->aggcontexts[i]);
		}

		/*
		 * Check if input is complete and there are no more groups to project
		 * in this phase; move to next phase or mark as done.
		 */
		if (aggstate->input_done == true &&
			aggstate->projected_set >= (numGroupingSets - 1))
		{
			if (aggstate->current_phase < aggstate->numphases - 1)
			{
				initialize_phase(aggstate, aggstate->current_phase + 1);
				aggstate->input_done = false;
				aggstate->projected_set = -1;
				numGroupingSets = Max(aggstate->phase->numsets, 1);
				node = aggstate->phase->aggnode;
				numReset = numGroupingSets;
			}
			else
			{
				aggstate->agg_done = true;
				break;
			}
		}

		/*
		 * Get the number of columns in the next grouping set after the last
		 * projected one (if any). This is the number of columns to compare to
		 * see if we reached the boundary of that set too.
		 */
		if (aggstate->projected_set >= 0 &&
			aggstate->projected_set < (numGroupingSets - 1))
			nextSetSize = aggstate->phase->gset_lengths[aggstate->projected_set + 1];
		else
			nextSetSize = 0;

		/*----------
		 * If a subgroup for the current grouping set is present, project it.
		 *
		 * We have a new group if:
		 *	- we're out of input but haven't projected all grouping sets
		 *	  (checked above)
		 * OR
		 *	  - we already projected a row that wasn't from the last grouping
		 *		set
		 *	  AND
		 *	  - the next grouping set has at least one grouping column (since
		 *		empty grouping sets project only once input is exhausted)
		 *	  AND
		 *	  - the previous and pending rows differ on the grouping columns
		 *		of the next grouping set
		 *----------
		 */
		if (aggstate->input_done ||
			(node->aggstrategy == AGG_SORTED &&
			 aggstate->projected_set != -1 &&
			 aggstate->projected_set < (numGroupingSets - 1) &&
			 nextSetSize > 0 &&
			 !execTuplesMatch(econtext->ecxt_outertuple,
							  tmpcontext->ecxt_outertuple,
							  nextSetSize,
							  node->grpColIdx,
							  aggstate->phase->eqfunctions,
							  tmpcontext->ecxt_per_tuple_memory)))
		{
			aggstate->projected_set += 1;

			Assert(aggstate->projected_set < numGroupingSets);
			Assert(nextSetSize > 0 || aggstate->input_done);
		}
		else
		{
			/*
			 * We no longer care what group we just projected, the next
			 * projection will always be the first (or only) grouping set
			 * (unless the input proves to be empty).
			 */
			aggstate->projected_set = 0;

			/*
			 * If we don't already have the first tuple of the new group,
			 * fetch it from the outer plan.
			 */
			if (aggstate->grp_firstTuple == NULL)
			{
				outerslot = fetch_input_tuple(aggstate);
				if (!TupIsNull(outerslot))
				{
					/*
					 * Make a copy of the first input tuple; we will use this
					 * for comparisons (in group mode) and for projection.
					 */
					aggstate->grp_firstTuple = ExecCopySlotTuple(outerslot);
				}
				else
				{
					/* outer plan produced no tuples at all */
					if (hasGroupingSets)
					{
						/*
						 * If there was no input at all, we need to project
						 * rows only if there are grouping sets of size 0.
						 * Note that this implies that there can't be any
						 * references to ungrouped Vars, which would otherwise
						 * cause issues with the empty output slot.
						 *
						 * XXX: This is no longer true, we currently deal with
						 * this in finalize_aggregates().
						 */
						aggstate->input_done = true;

						while (aggstate->phase->gset_lengths[aggstate->projected_set] > 0)
						{
							aggstate->projected_set += 1;
							if (aggstate->projected_set >= numGroupingSets)
							{
								/*
								 * We can't set agg_done here because we might
								 * have more phases to do, even though the
								 * input is empty. So we need to restart the
								 * whole outer loop.
								 */
								break;
							}
						}

						if (aggstate->projected_set >= numGroupingSets)
							continue;
					}
					else
					{
						aggstate->agg_done = true;
						/* If we are grouping, we should produce no tuples too */
						if (node->aggstrategy != AGG_PLAIN)
							return NULL;
					}
				}
			}

			/*
			 * Initialize working state for a new input tuple group.
			 */
			initialize_aggregates(aggstate, pergroup, numReset);

			if (aggstate->grp_firstTuple != NULL)
			{
				/*
				 * Store the copied first input tuple in the tuple table slot
				 * reserved for it.  The tuple will be deleted when it is
				 * cleared from the slot.
				 */
				ExecStoreTuple(aggstate->grp_firstTuple,
							   firstSlot,
							   InvalidBuffer,
							   true);
				aggstate->grp_firstTuple = NULL;		/* don't keep two
														 * pointers */

				/* set up for first advance_aggregates call */
				tmpcontext->ecxt_outertuple = firstSlot;

				/*
				 * Process each outer-plan tuple, and then fetch the next one,
				 * until we exhaust the outer plan or cross a group boundary.
				 */
				for (;;)
				{
					if (DO_AGGSPLIT_COMBINE(aggstate->aggsplit))
						combine_aggregates(aggstate, pergroup);
					else
						advance_aggregates(aggstate, pergroup);

					/* Reset per-input-tuple context after each tuple */
					ResetExprContext(tmpcontext);

					outerslot = fetch_input_tuple(aggstate);
					if (TupIsNull(outerslot))
					{
						/* no more outer-plan tuples available */
						if (hasGroupingSets)
						{
							aggstate->input_done = true;
							break;
						}
						else
						{
							aggstate->agg_done = true;
							break;
						}
					}
					/* set up for next advance_aggregates call */
					tmpcontext->ecxt_outertuple = outerslot;

					/*
					 * If we are grouping, check whether we've crossed a group
					 * boundary.
					 */
					if (node->aggstrategy == AGG_SORTED)
					{
						if (!execTuplesMatch(firstSlot,
											 outerslot,
											 node->numCols,
											 node->grpColIdx,
											 aggstate->phase->eqfunctions,
										  tmpcontext->ecxt_per_tuple_memory))
						{
							aggstate->grp_firstTuple = ExecCopySlotTuple(outerslot);
							break;
						}
					}
				}
			}

			/*
			 * Use the representative input tuple for any references to
			 * non-aggregated input columns in aggregate direct args, the node
			 * qual, and the tlist.  (If we are not grouping, and there are no
			 * input rows at all, we will come here with an empty firstSlot
			 * ... but if not grouping, there can't be any references to
			 * non-aggregated input columns, so no problem.)
			 */
			econtext->ecxt_outertuple = firstSlot;
		}

		Assert(aggstate->projected_set >= 0);

		currentSet = aggstate->projected_set;

		prepare_projection_slot(aggstate, econtext->ecxt_outertuple, currentSet);

		finalize_aggregates(aggstate, peragg, pergroup, currentSet);

		/*
		 * If there's no row to project right now, we must continue rather
		 * than returning a null since there might be more groups.
		 */
		result = project_aggregates(aggstate);
		if (result)
			return result;
	}

	/* No more groups */
	return NULL;
}

/*
 * ExecAgg for hashed case: phase 1, read input and build hash table
 */
static void
agg_fill_hash_table(AggState *aggstate)
{
	ExprContext *tmpcontext;
	AggHashEntry entry;
	TupleTableSlot *outerslot;

	/*
	 * get state info from node
	 *
	 * tmpcontext is the per-input-tuple expression context
	 */
	tmpcontext = aggstate->tmpcontext;

	/*
	 * Process each outer-plan tuple, and then fetch the next one, until we
	 * exhaust the outer plan.
	 */
	for (;;)
	{
		outerslot = fetch_input_tuple(aggstate);
		if (TupIsNull(outerslot))
			break;
		/* set up for advance_aggregates call */
		tmpcontext->ecxt_outertuple = outerslot;

		/* Find or build hashtable entry for this tuple's group */
		entry = lookup_hash_entry(aggstate, outerslot);

		/* Advance the aggregates */
		if (DO_AGGSPLIT_COMBINE(aggstate->aggsplit))
			combine_aggregates(aggstate, entry->pergroup);
		else
			advance_aggregates(aggstate, entry->pergroup);

		/* Reset per-input-tuple context after each tuple */
		ResetExprContext(tmpcontext);
	}

	aggstate->table_filled = true;
	/* Initialize to walk the hash table */
	ResetTupleHashIterator(aggstate->hashtable, &aggstate->hashiter);
}

/*
 * ExecAgg for hashed case: phase 2, retrieving groups from hash table
 */
static TupleTableSlot *
agg_retrieve_hash_table(AggState *aggstate)
{
	ExprContext *econtext;
	AggStatePerAgg peragg;
	AggStatePerGroup pergroup;
	AggHashEntry entry;
	TupleTableSlot *firstSlot;
	TupleTableSlot *result;

	/*
	 * get state info from node
	 */
	/* econtext is the per-output-tuple expression context */
	econtext = aggstate->ss.ps.ps_ExprContext;
	peragg = aggstate->peragg;
	firstSlot = aggstate->ss.ss_ScanTupleSlot;

	/*
	 * We loop retrieving groups until we find one satisfying
	 * aggstate->ss.ps.qual
	 */
	while (!aggstate->agg_done)
	{
		/*
		 * Find the next entry in the hash table
		 */
		entry = (AggHashEntry) ScanTupleHashTable(&aggstate->hashiter);
		if (entry == NULL)
		{
			/* No more entries in hashtable, so done */
			aggstate->agg_done = TRUE;
			return NULL;
		}

		/*
		 * Clear the per-output-tuple context for each group
		 *
		 * We intentionally don't use ReScanExprContext here; if any aggs have
		 * registered shutdown callbacks, they mustn't be called yet, since we
		 * might not be done with that agg.
		 */
		ResetExprContext(econtext);

		/*
		 * Store the copied first input tuple in the tuple table slot reserved
		 * for it, so that it can be used in ExecProject.
		 */
		ExecStoreMinimalTuple(entry->shared.firstTuple,
							  firstSlot,
							  false);

		pergroup = entry->pergroup;

		finalize_aggregates(aggstate, peragg, pergroup, 0);

		/*
		 * Use the representative input tuple for any references to
		 * non-aggregated input columns in the qual and tlist.
		 */
		econtext->ecxt_outertuple = firstSlot;

		result = project_aggregates(aggstate);
		if (result)
			return result;
	}

	/* No more groups */
	return NULL;
}

/* -----------------
 * ExecInitAgg
 *
 *	Creates the run-time information for the agg node produced by the
 *	planner and initializes its outer subtree
 * -----------------
 */
AggState *
ExecInitAgg(Agg *node, EState *estate, int eflags)
{
	AggState   *aggstate;
	AggStatePerAgg peraggs;
	AggStatePerTrans pertransstates;
	Plan	   *outerPlan;
	ExprContext *econtext;
	int			numaggs,
				transno,
				aggno;
	int			phase;
	ListCell   *l;
	Bitmapset  *all_grouped_cols = NULL;
	int			numGroupingSets = 1;
	int			numPhases;
	int			i = 0;
	int			j = 0;

	/* check for unsupported flags */
	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));

	/*
	 * create state structure
	 */
	aggstate = makeNode(AggState);
	aggstate->ss.ps.plan = (Plan *) node;
	aggstate->ss.ps.state = estate;

	aggstate->aggs = NIL;
	aggstate->numaggs = 0;
	aggstate->numtrans = 0;
	aggstate->aggsplit = node->aggsplit;
	aggstate->maxsets = 0;
	aggstate->hashfunctions = NULL;
	aggstate->projected_set = -1;
	aggstate->current_set = 0;
	aggstate->peragg = NULL;
	aggstate->pertrans = NULL;
	aggstate->curpertrans = NULL;
	aggstate->input_done = false;
	aggstate->agg_done = false;
	aggstate->pergroup = NULL;
	aggstate->grp_firstTuple = NULL;
	aggstate->hashtable = NULL;
	aggstate->sort_in = NULL;
	aggstate->sort_out = NULL;

	/*
	 * Calculate the maximum number of grouping sets in any phase; this
	 * determines the size of some allocations.
	 */
	if (node->groupingSets)
	{
		Assert(node->aggstrategy != AGG_HASHED);

		numGroupingSets = list_length(node->groupingSets);

		foreach(l, node->chain)
		{
			Agg		   *agg = lfirst(l);

			numGroupingSets = Max(numGroupingSets,
								  list_length(agg->groupingSets));
		}
	}

	aggstate->maxsets = numGroupingSets;
	aggstate->numphases = numPhases = 1 + list_length(node->chain);

	aggstate->aggcontexts = (ExprContext **)
		palloc0(sizeof(ExprContext *) * numGroupingSets);

	/*
	 * Create expression contexts.  We need three or more, one for
	 * per-input-tuple processing, one for per-output-tuple processing, and
	 * one for each grouping set.  The per-tuple memory context of the
	 * per-grouping-set ExprContexts (aggcontexts) replaces the standalone
	 * memory context formerly used to hold transition values.  We cheat a
	 * little by using ExecAssignExprContext() to build all of them.
	 *
	 * NOTE: the details of what is stored in aggcontexts and what is stored
	 * in the regular per-query memory context are driven by a simple
	 * decision: we want to reset the aggcontext at group boundaries (if not
	 * hashing) and in ExecReScanAgg to recover no-longer-wanted space.
	 */
	ExecAssignExprContext(estate, &aggstate->ss.ps);
	aggstate->tmpcontext = aggstate->ss.ps.ps_ExprContext;

	for (i = 0; i < numGroupingSets; ++i)
	{
		ExecAssignExprContext(estate, &aggstate->ss.ps);
		aggstate->aggcontexts[i] = aggstate->ss.ps.ps_ExprContext;
	}

	ExecAssignExprContext(estate, &aggstate->ss.ps);

	/*
	 * tuple table initialization
	 */
	ExecInitScanTupleSlot(estate, &aggstate->ss);
	ExecInitResultTupleSlot(estate, &aggstate->ss.ps);
	aggstate->hashslot = ExecInitExtraTupleSlot(estate);
	aggstate->sort_slot = ExecInitExtraTupleSlot(estate);

	/*
	 * initialize child expressions
	 *
	 * Note: ExecInitExpr finds Aggrefs for us, and also checks that no aggs
	 * contain other agg calls in their arguments.  This would make no sense
	 * under SQL semantics anyway (and it's forbidden by the spec). Because
	 * that is true, we don't need to worry about evaluating the aggs in any
	 * particular order.
	 */
	aggstate->ss.ps.targetlist = (List *)
		ExecInitExpr((Expr *) node->plan.targetlist,
					 (PlanState *) aggstate);
	aggstate->ss.ps.qual = (List *)
		ExecInitExpr((Expr *) node->plan.qual,
					 (PlanState *) aggstate);

	/*
	 * Initialize child nodes.
	 *
	 * If we are doing a hashed aggregation then the child plan does not need
	 * to handle REWIND efficiently; see ExecReScanAgg.
	 */
	if (node->aggstrategy == AGG_HASHED)
		eflags &= ~EXEC_FLAG_REWIND;
	outerPlan = outerPlan(node);
	outerPlanState(aggstate) = ExecInitNode(outerPlan, estate, eflags);

	/*
	 * initialize source tuple type.
	 */
	ExecAssignScanTypeFromOuterPlan(&aggstate->ss);
	if (node->chain)
		ExecSetSlotDescriptor(aggstate->sort_slot,
						 aggstate->ss.ss_ScanTupleSlot->tts_tupleDescriptor);

	/*
	 * Initialize result tuple type and projection info.
	 */
	ExecAssignResultTypeFromTL(&aggstate->ss.ps);
	ExecAssignProjectionInfo(&aggstate->ss.ps, NULL);

	aggstate->ss.ps.ps_TupFromTlist = false;

	/*
	 * get the count of aggregates in targetlist and quals
	 */
	numaggs = aggstate->numaggs;
	Assert(numaggs == list_length(aggstate->aggs));
	if (numaggs <= 0)
	{
		/*
		 * This is not an error condition: we might be using the Agg node just
		 * to do hash-based grouping.  Even in the regular case,
		 * constant-expression simplification could optimize away all of the
		 * Aggrefs in the targetlist and qual.  So keep going, but force local
		 * copy of numaggs positive so that palloc()s below don't choke.
		 */
		numaggs = 1;
	}

	/*
	 * For each phase, prepare grouping set data and fmgr lookup data for
	 * compare functions.  Accumulate all_grouped_cols in passing.
	 */

	aggstate->phases = palloc0(numPhases * sizeof(AggStatePerPhaseData));

	for (phase = 0; phase < numPhases; ++phase)
	{
		AggStatePerPhase phasedata = &aggstate->phases[phase];
		Agg		   *aggnode;
		Sort	   *sortnode;
		int			num_sets;

		if (phase > 0)
		{
			aggnode = list_nth(node->chain, phase - 1);
			sortnode = (Sort *) aggnode->plan.lefttree;
			Assert(IsA(sortnode, Sort));
		}
		else
		{
			aggnode = node;
			sortnode = NULL;
		}

		phasedata->numsets = num_sets = list_length(aggnode->groupingSets);

		if (num_sets)
		{
			phasedata->gset_lengths = palloc(num_sets * sizeof(int));
			phasedata->grouped_cols = palloc(num_sets * sizeof(Bitmapset *));

			i = 0;
			foreach(l, aggnode->groupingSets)
			{
				int			current_length = list_length(lfirst(l));
				Bitmapset  *cols = NULL;

				/* planner forces this to be correct */
				for (j = 0; j < current_length; ++j)
					cols = bms_add_member(cols, aggnode->grpColIdx[j]);

				phasedata->grouped_cols[i] = cols;
				phasedata->gset_lengths[i] = current_length;
				++i;
			}

			all_grouped_cols = bms_add_members(all_grouped_cols,
											   phasedata->grouped_cols[0]);
		}
		else
		{
			Assert(phase == 0);

			phasedata->gset_lengths = NULL;
			phasedata->grouped_cols = NULL;
		}

		/*
		 * If we are grouping, precompute fmgr lookup data for inner loop.
		 */
		if (aggnode->aggstrategy == AGG_SORTED)
		{
			Assert(aggnode->numCols > 0);

			phasedata->eqfunctions =
				execTuplesMatchPrepare(aggnode->numCols,
									   aggnode->grpOperators);
		}

		phasedata->aggnode = aggnode;
		phasedata->sortnode = sortnode;
	}

	/*
	 * Convert all_grouped_cols to a descending-order list.
	 */
	i = -1;
	while ((i = bms_next_member(all_grouped_cols, i)) >= 0)
		aggstate->all_grouped_cols = lcons_int(i, aggstate->all_grouped_cols);

	/*
	 * Hashing can only appear in the initial phase.
	 */

	if (node->aggstrategy == AGG_HASHED)
		execTuplesHashPrepare(node->numCols,
							  node->grpOperators,
							  &aggstate->phases[0].eqfunctions,
							  &aggstate->hashfunctions);

	/*
	 * Initialize current phase-dependent values to initial phase
	 */

	aggstate->current_phase = 0;
	initialize_phase(aggstate, 0);

	/*
	 * Set up aggregate-result storage in the output expr context, and also
	 * allocate my private per-agg working storage
	 */
	econtext = aggstate->ss.ps.ps_ExprContext;
	econtext->ecxt_aggvalues = (Datum *) palloc0(sizeof(Datum) * numaggs);
	econtext->ecxt_aggnulls = (bool *) palloc0(sizeof(bool) * numaggs);

	peraggs = (AggStatePerAgg) palloc0(sizeof(AggStatePerAggData) * numaggs);
	pertransstates = (AggStatePerTrans) palloc0(sizeof(AggStatePerTransData) * numaggs);

	aggstate->peragg = peraggs;
	aggstate->pertrans = pertransstates;

	if (node->aggstrategy == AGG_HASHED)
	{
		build_hash_table(aggstate);
		aggstate->table_filled = false;
		/* Compute the columns we actually need to hash on */
		aggstate->hash_needed = find_hash_columns(aggstate);
	}
	else
	{
		AggStatePerGroup pergroup;

		pergroup = (AggStatePerGroup) palloc0(sizeof(AggStatePerGroupData)
											  * numaggs
											  * numGroupingSets);

		aggstate->pergroup = pergroup;
	}

	/* -----------------
	 * Perform lookups of aggregate function info, and initialize the
	 * unchanging fields of the per-agg and per-trans data.
	 *
	 * We try to optimize by detecting duplicate aggregate functions so that
	 * their state and final values are re-used, rather than needlessly being
	 * re-calculated independently. We also detect aggregates that are not
	 * the same, but which can share the same transition state.
	 *
	 * Scenarios:
	 *
	 * 1. An aggregate function appears more than once in query:
	 *
	 *	  SELECT SUM(x) FROM ... HAVING SUM(x) > 0
	 *
	 *	  Since the aggregates are the identical, we only need to calculate
	 *	  the calculate it once. Both aggregates will share the same 'aggno'
	 *	  value.
	 *
	 * 2. Two different aggregate functions appear in the query, but the
	 *	  aggregates have the same transition function and initial value, but
	 *	  different final function:
	 *
	 *	  SELECT SUM(x), AVG(x) FROM ...
	 *
	 *	  In this case we must create a new peragg for the varying aggregate,
	 *	  and need to call the final functions separately, but can share the
	 *	  same transition state.
	 *
	 * For either of these optimizations to be valid, the aggregate's
	 * arguments must be the same, including any modifiers such as ORDER BY,
	 * DISTINCT and FILTER, and they mustn't contain any volatile functions.
	 * -----------------
	 */
	aggno = -1;
	transno = -1;
	foreach(l, aggstate->aggs)
	{
		AggrefExprState *aggrefstate = (AggrefExprState *) lfirst(l);
		Aggref	   *aggref = (Aggref *) aggrefstate->xprstate.expr;
		AggStatePerAgg peragg;
		AggStatePerTrans pertrans;
		int			existing_aggno;
		int			existing_transno;
		List	   *same_input_transnos;
		Oid			inputTypes[FUNC_MAX_ARGS];
		int			numArguments;
		int			numDirectArgs;
		HeapTuple	aggTuple;
		Form_pg_aggregate aggform;
		AclResult	aclresult;
		Oid			transfn_oid,
					finalfn_oid;
		Oid			serialfn_oid,
					deserialfn_oid;
		Expr	   *finalfnexpr;
		Oid			aggtranstype;
		Datum		textInitVal;
		Datum		initValue;
		bool		initValueIsNull;

		/* Planner should have assigned aggregate to correct level */
		Assert(aggref->agglevelsup == 0);
		/* ... and the split mode should match */
		Assert(aggref->aggsplit == aggstate->aggsplit);

		/* 1. Check for already processed aggs which can be re-used */
		existing_aggno = find_compatible_peragg(aggref, aggstate, aggno,
												&same_input_transnos);
		if (existing_aggno != -1)
		{
			/*
			 * Existing compatible agg found. so just point the Aggref to the
			 * same per-agg struct.
			 */
			aggrefstate->aggno = existing_aggno;
			continue;
		}

		/* Mark Aggref state node with assigned index in the result array */
		peragg = &peraggs[++aggno];
		peragg->aggref = aggref;
		aggrefstate->aggno = aggno;

		/* Fetch the pg_aggregate row */
		aggTuple = SearchSysCache1(AGGFNOID,
								   ObjectIdGetDatum(aggref->aggfnoid));
		if (!HeapTupleIsValid(aggTuple))
			elog(ERROR, "cache lookup failed for aggregate %u",
				 aggref->aggfnoid);
		aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);

		/* Check permission to call aggregate function */
		aclresult = pg_proc_aclcheck(aggref->aggfnoid, GetUserId(),
									 ACL_EXECUTE);
		if (aclresult != ACLCHECK_OK)
			aclcheck_error(aclresult, ACL_KIND_PROC,
						   get_func_name(aggref->aggfnoid));
		InvokeFunctionExecuteHook(aggref->aggfnoid);

		/* planner recorded transition state type in the Aggref itself */
		aggtranstype = aggref->aggtranstype;
		Assert(OidIsValid(aggtranstype));

		/*
		 * If this aggregation is performing state combines, then instead of
		 * using the transition function, we'll use the combine function
		 */
		if (DO_AGGSPLIT_COMBINE(aggstate->aggsplit))
		{
			transfn_oid = aggform->aggcombinefn;

			/* If not set then the planner messed up */
			if (!OidIsValid(transfn_oid))
				elog(ERROR, "combinefn not set for aggregate function");
		}
		else
			transfn_oid = aggform->aggtransfn;

		/* Final function only required if we're finalizing the aggregates */
		if (DO_AGGSPLIT_SKIPFINAL(aggstate->aggsplit))
			peragg->finalfn_oid = finalfn_oid = InvalidOid;
		else
			peragg->finalfn_oid = finalfn_oid = aggform->aggfinalfn;

		serialfn_oid = InvalidOid;
		deserialfn_oid = InvalidOid;

		/*
		 * Check if serialization/deserialization is required.  We only do it
		 * for aggregates that have transtype INTERNAL.
		 */
		if (aggtranstype == INTERNALOID)
		{
			/*
			 * The planner should only have generated a serialize agg node if
			 * every aggregate with an INTERNAL state has a serialization
			 * function.  Verify that.
			 */
			if (DO_AGGSPLIT_SERIALIZE(aggstate->aggsplit))
			{
				/* serialization only valid when not running finalfn */
				Assert(DO_AGGSPLIT_SKIPFINAL(aggstate->aggsplit));

				if (!OidIsValid(aggform->aggserialfn))
					elog(ERROR, "serialfunc not provided for serialization aggregation");
				serialfn_oid = aggform->aggserialfn;
			}

			/* Likewise for deserialization functions */
			if (DO_AGGSPLIT_DESERIALIZE(aggstate->aggsplit))
			{
				/* deserialization only valid when combining states */
				Assert(DO_AGGSPLIT_COMBINE(aggstate->aggsplit));

				if (!OidIsValid(aggform->aggdeserialfn))
					elog(ERROR, "deserialfunc not provided for deserialization aggregation");
				deserialfn_oid = aggform->aggdeserialfn;
			}
		}

		/* Check that aggregate owner has permission to call component fns */
		{
			HeapTuple	procTuple;
			Oid			aggOwner;

			procTuple = SearchSysCache1(PROCOID,
										ObjectIdGetDatum(aggref->aggfnoid));
			if (!HeapTupleIsValid(procTuple))
				elog(ERROR, "cache lookup failed for function %u",
					 aggref->aggfnoid);
			aggOwner = ((Form_pg_proc) GETSTRUCT(procTuple))->proowner;
			ReleaseSysCache(procTuple);

			aclresult = pg_proc_aclcheck(transfn_oid, aggOwner,
										 ACL_EXECUTE);
			if (aclresult != ACLCHECK_OK)
				aclcheck_error(aclresult, ACL_KIND_PROC,
							   get_func_name(transfn_oid));
			InvokeFunctionExecuteHook(transfn_oid);
			if (OidIsValid(finalfn_oid))
			{
				aclresult = pg_proc_aclcheck(finalfn_oid, aggOwner,
											 ACL_EXECUTE);
				if (aclresult != ACLCHECK_OK)
					aclcheck_error(aclresult, ACL_KIND_PROC,
								   get_func_name(finalfn_oid));
				InvokeFunctionExecuteHook(finalfn_oid);
			}
			if (OidIsValid(serialfn_oid))
			{
				aclresult = pg_proc_aclcheck(serialfn_oid, aggOwner,
											 ACL_EXECUTE);
				if (aclresult != ACLCHECK_OK)
					aclcheck_error(aclresult, ACL_KIND_PROC,
								   get_func_name(serialfn_oid));
				InvokeFunctionExecuteHook(serialfn_oid);
			}
			if (OidIsValid(deserialfn_oid))
			{
				aclresult = pg_proc_aclcheck(deserialfn_oid, aggOwner,
											 ACL_EXECUTE);
				if (aclresult != ACLCHECK_OK)
					aclcheck_error(aclresult, ACL_KIND_PROC,
								   get_func_name(deserialfn_oid));
				InvokeFunctionExecuteHook(deserialfn_oid);
			}
		}

		/*
		 * Get actual datatypes of the (nominal) aggregate inputs.  These
		 * could be different from the agg's declared input types, when the
		 * agg accepts ANY or a polymorphic type.
		 */
		numArguments = get_aggregate_argtypes(aggref, inputTypes);

		/* Count the "direct" arguments, if any */
		numDirectArgs = list_length(aggref->aggdirectargs);

		/* Detect how many arguments to pass to the finalfn */
		if (aggform->aggfinalextra)
			peragg->numFinalArgs = numArguments + 1;
		else
			peragg->numFinalArgs = numDirectArgs + 1;

		/*
		 * build expression trees using actual argument & result types for the
		 * finalfn, if it exists and is required.
		 */
		if (OidIsValid(finalfn_oid))
		{
			build_aggregate_finalfn_expr(inputTypes,
										 peragg->numFinalArgs,
										 aggtranstype,
										 aggref->aggtype,
										 aggref->inputcollid,
										 finalfn_oid,
										 &finalfnexpr);
			fmgr_info(finalfn_oid, &peragg->finalfn);
			fmgr_info_set_expr((Node *) finalfnexpr, &peragg->finalfn);
		}

		/* get info about the output value's datatype */
		get_typlenbyval(aggref->aggtype,
						&peragg->resulttypeLen,
						&peragg->resulttypeByVal);

		/*
		 * initval is potentially null, so don't try to access it as a struct
		 * field. Must do it the hard way with SysCacheGetAttr.
		 */
		textInitVal = SysCacheGetAttr(AGGFNOID, aggTuple,
									  Anum_pg_aggregate_agginitval,
									  &initValueIsNull);
		if (initValueIsNull)
			initValue = (Datum) 0;
		else
			initValue = GetAggInitVal(textInitVal, aggtranstype);

		/*
		 * 2. Build working state for invoking the transition function, or
		 * look up previously initialized working state, if we can share it.
		 *
		 * find_compatible_peragg() already collected a list of per-Trans's
		 * with the same inputs. Check if any of them have the same transition
		 * function and initial value.
		 */
		existing_transno = find_compatible_pertrans(aggstate, aggref,
													transfn_oid, aggtranstype,
												serialfn_oid, deserialfn_oid,
												  initValue, initValueIsNull,
													same_input_transnos);
		if (existing_transno != -1)
		{
			/*
			 * Existing compatible trans found, so just point the 'peragg' to
			 * the same per-trans struct.
			 */
			pertrans = &pertransstates[existing_transno];
			peragg->transno = existing_transno;
		}
		else
		{
			pertrans = &pertransstates[++transno];
			build_pertrans_for_aggref(pertrans, aggstate, estate,
									  aggref, transfn_oid, aggtranstype,
									  serialfn_oid, deserialfn_oid,
									  initValue, initValueIsNull,
									  inputTypes, numArguments);
			peragg->transno = transno;
		}
		ReleaseSysCache(aggTuple);
	}

	/*
	 * Update numaggs to match the number of unique aggregates found. Also set
	 * numstates to the number of unique aggregate states found.
	 */
	aggstate->numaggs = aggno + 1;
	aggstate->numtrans = transno + 1;

	return aggstate;
}

/*
 * Build the state needed to calculate a state value for an aggregate.
 *
 * This initializes all the fields in 'pertrans'. 'aggref' is the aggregate
 * to initialize the state for. 'aggtransfn', 'aggtranstype', and the rest
 * of the arguments could be calculated from 'aggref', but the caller has
 * calculated them already, so might as well pass them.
 */
static void
build_pertrans_for_aggref(AggStatePerTrans pertrans,
						  AggState *aggstate, EState *estate,
						  Aggref *aggref,
						  Oid aggtransfn, Oid aggtranstype,
						  Oid aggserialfn, Oid aggdeserialfn,
						  Datum initValue, bool initValueIsNull,
						  Oid *inputTypes, int numArguments)
{
	int			numGroupingSets = Max(aggstate->maxsets, 1);
	Expr	   *serialfnexpr = NULL;
	Expr	   *deserialfnexpr = NULL;
	ListCell   *lc;
	int			numInputs;
	int			numDirectArgs;
	List	   *sortlist;
	int			numSortCols;
	int			numDistinctCols;
	int			naggs;
	int			i;

	/* Begin filling in the pertrans data */
	pertrans->aggref = aggref;
	pertrans->aggCollation = aggref->inputcollid;
	pertrans->transfn_oid = aggtransfn;
	pertrans->serialfn_oid = aggserialfn;
	pertrans->deserialfn_oid = aggdeserialfn;
	pertrans->initValue = initValue;
	pertrans->initValueIsNull = initValueIsNull;

	/* Count the "direct" arguments, if any */
	numDirectArgs = list_length(aggref->aggdirectargs);

	/* Count the number of aggregated input columns */
	pertrans->numInputs = numInputs = list_length(aggref->args);

	pertrans->aggtranstype = aggtranstype;

	/* Detect how many arguments to pass to the transfn */
	if (AGGKIND_IS_ORDERED_SET(aggref->aggkind))
		pertrans->numTransInputs = numInputs;
	else
		pertrans->numTransInputs = numArguments;

	/*
	 * When combining states, we have no use at all for the aggregate
	 * function's transfn. Instead we use the combinefn.  In this case, the
	 * transfn and transfn_oid fields of pertrans refer to the combine
	 * function rather than the transition function.
	 */
	if (DO_AGGSPLIT_COMBINE(aggstate->aggsplit))
	{
		Expr	   *combinefnexpr;

		build_aggregate_combinefn_expr(aggtranstype,
									   aggref->inputcollid,
									   aggtransfn,
									   &combinefnexpr);
		fmgr_info(aggtransfn, &pertrans->transfn);
		fmgr_info_set_expr((Node *) combinefnexpr, &pertrans->transfn);

		InitFunctionCallInfoData(pertrans->transfn_fcinfo,
								 &pertrans->transfn,
								 2,
								 pertrans->aggCollation,
								 (void *) aggstate, NULL);

		/*
		 * Ensure that a combine function to combine INTERNAL states is not
		 * strict. This should have been checked during CREATE AGGREGATE, but
		 * the strict property could have been changed since then.
		 */
		if (pertrans->transfn.fn_strict && aggtranstype == INTERNALOID)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
					 errmsg("combine function for aggregate %u must to be declared as strict",
							aggref->aggfnoid)));
	}
	else
	{
		Expr	   *transfnexpr;

		/*
		 * Set up infrastructure for calling the transfn.  Note that invtrans
		 * is not needed here.
		 */
		build_aggregate_transfn_expr(inputTypes,
									 numArguments,
									 numDirectArgs,
									 aggref->aggvariadic,
									 aggtranstype,
									 aggref->inputcollid,
									 aggtransfn,
									 InvalidOid,
									 &transfnexpr,
									 NULL);
		fmgr_info(aggtransfn, &pertrans->transfn);
		fmgr_info_set_expr((Node *) transfnexpr, &pertrans->transfn);

		InitFunctionCallInfoData(pertrans->transfn_fcinfo,
								 &pertrans->transfn,
								 pertrans->numTransInputs + 1,
								 pertrans->aggCollation,
								 (void *) aggstate, NULL);

		/*
		 * If the transfn is strict and the initval is NULL, make sure input
		 * type and transtype are the same (or at least binary-compatible), so
		 * that it's OK to use the first aggregated input value as the initial
		 * transValue.  This should have been checked at agg definition time,
		 * but we must check again in case the transfn's strictness property
		 * has been changed.
		 */
		if (pertrans->transfn.fn_strict && pertrans->initValueIsNull)
		{
			if (numArguments <= numDirectArgs ||
				!IsBinaryCoercible(inputTypes[numDirectArgs],
								   aggtranstype))
				ereport(ERROR,
						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
						 errmsg("aggregate %u needs to have compatible input type and transition type",
								aggref->aggfnoid)));
		}
	}

	/* get info about the state value's datatype */
	get_typlenbyval(aggtranstype,
					&pertrans->transtypeLen,
					&pertrans->transtypeByVal);

	if (OidIsValid(aggserialfn))
	{
		build_aggregate_serialfn_expr(aggserialfn,
									  &serialfnexpr);
		fmgr_info(aggserialfn, &pertrans->serialfn);
		fmgr_info_set_expr((Node *) serialfnexpr, &pertrans->serialfn);

		InitFunctionCallInfoData(pertrans->serialfn_fcinfo,
								 &pertrans->serialfn,
								 1,
								 InvalidOid,
								 (void *) aggstate, NULL);
	}

	if (OidIsValid(aggdeserialfn))
	{
		build_aggregate_deserialfn_expr(aggdeserialfn,
										&deserialfnexpr);
		fmgr_info(aggdeserialfn, &pertrans->deserialfn);
		fmgr_info_set_expr((Node *) deserialfnexpr, &pertrans->deserialfn);

		InitFunctionCallInfoData(pertrans->deserialfn_fcinfo,
								 &pertrans->deserialfn,
								 2,
								 InvalidOid,
								 (void *) aggstate, NULL);

	}

	/*
	 * Get a tupledesc corresponding to the aggregated inputs (including sort
	 * expressions) of the agg.
	 */
	pertrans->evaldesc = ExecTypeFromTL(aggref->args, false);

	/* Create slot we're going to do argument evaluation in */
	pertrans->evalslot = ExecInitExtraTupleSlot(estate);
	ExecSetSlotDescriptor(pertrans->evalslot, pertrans->evaldesc);

	/* Initialize the input and FILTER expressions */
	naggs = aggstate->numaggs;
	pertrans->aggfilter = ExecInitExpr(aggref->aggfilter,
									   (PlanState *) aggstate);
	pertrans->aggdirectargs = (List *) ExecInitExpr((Expr *) aggref->aggdirectargs,
													(PlanState *) aggstate);
	pertrans->args = (List *) ExecInitExpr((Expr *) aggref->args,
										   (PlanState *) aggstate);

	/*
	 * Complain if the aggregate's arguments contain any aggregates; nested
	 * agg functions are semantically nonsensical.  (This should have been
	 * caught earlier, but we defend against it here anyway.)
	 */
	if (naggs != aggstate->numaggs)
		ereport(ERROR,
				(errcode(ERRCODE_GROUPING_ERROR),
				 errmsg("aggregate function calls cannot be nested")));

	/* Set up projection info for evaluation */
	pertrans->evalproj = ExecBuildProjectionInfo(pertrans->args,
												 aggstate->tmpcontext,
												 pertrans->evalslot,
												 NULL);

	/*
	 * If we're doing either DISTINCT or ORDER BY for a plain agg, then we
	 * have a list of SortGroupClause nodes; fish out the data in them and
	 * stick them into arrays.  We ignore ORDER BY for an ordered-set agg,
	 * however; the agg's transfn and finalfn are responsible for that.
	 *
	 * Note that by construction, if there is a DISTINCT clause then the ORDER
	 * BY clause is a prefix of it (see transformDistinctClause).
	 */
	if (AGGKIND_IS_ORDERED_SET(aggref->aggkind))
	{
		sortlist = NIL;
		numSortCols = numDistinctCols = 0;
	}
	else if (aggref->aggdistinct)
	{
		sortlist = aggref->aggdistinct;
		numSortCols = numDistinctCols = list_length(sortlist);
		Assert(numSortCols >= list_length(aggref->aggorder));
	}
	else
	{
		sortlist = aggref->aggorder;
		numSortCols = list_length(sortlist);
		numDistinctCols = 0;
	}

	pertrans->numSortCols = numSortCols;
	pertrans->numDistinctCols = numDistinctCols;

	if (numSortCols > 0)
	{
		/*
		 * We don't implement DISTINCT or ORDER BY aggs in the HASHED case
		 * (yet)
		 */
		Assert(((Agg *) aggstate->ss.ps.plan)->aggstrategy != AGG_HASHED);

		/* If we have only one input, we need its len/byval info. */
		if (numInputs == 1)
		{
			get_typlenbyval(inputTypes[numDirectArgs],
							&pertrans->inputtypeLen,
							&pertrans->inputtypeByVal);
		}
		else if (numDistinctCols > 0)
		{
			/* we will need an extra slot to store prior values */
			pertrans->uniqslot = ExecInitExtraTupleSlot(estate);
			ExecSetSlotDescriptor(pertrans->uniqslot,
								  pertrans->evaldesc);
		}

		/* Extract the sort information for use later */
		pertrans->sortColIdx =
			(AttrNumber *) palloc(numSortCols * sizeof(AttrNumber));
		pertrans->sortOperators =
			(Oid *) palloc(numSortCols * sizeof(Oid));
		pertrans->sortCollations =
			(Oid *) palloc(numSortCols * sizeof(Oid));
		pertrans->sortNullsFirst =
			(bool *) palloc(numSortCols * sizeof(bool));

		i = 0;
		foreach(lc, sortlist)
		{
			SortGroupClause *sortcl = (SortGroupClause *) lfirst(lc);
			TargetEntry *tle = get_sortgroupclause_tle(sortcl, aggref->args);

			/* the parser should have made sure of this */
			Assert(OidIsValid(sortcl->sortop));

			pertrans->sortColIdx[i] = tle->resno;
			pertrans->sortOperators[i] = sortcl->sortop;
			pertrans->sortCollations[i] = exprCollation((Node *) tle->expr);
			pertrans->sortNullsFirst[i] = sortcl->nulls_first;
			i++;
		}
		Assert(i == numSortCols);
	}

	if (aggref->aggdistinct)
	{
		Assert(numArguments > 0);

		/*
		 * We need the equal function for each DISTINCT comparison we will
		 * make.
		 */
		pertrans->equalfns =
			(FmgrInfo *) palloc(numDistinctCols * sizeof(FmgrInfo));

		i = 0;
		foreach(lc, aggref->aggdistinct)
		{
			SortGroupClause *sortcl = (SortGroupClause *) lfirst(lc);

			fmgr_info(get_opcode(sortcl->eqop), &pertrans->equalfns[i]);
			i++;
		}
		Assert(i == numDistinctCols);
	}

	pertrans->sortstates = (Tuplesortstate **)
		palloc0(sizeof(Tuplesortstate *) * numGroupingSets);
}


static Datum
GetAggInitVal(Datum textInitVal, Oid transtype)
{
	Oid			typinput,
				typioparam;
	char	   *strInitVal;
	Datum		initVal;

	getTypeInputInfo(transtype, &typinput, &typioparam);
	strInitVal = TextDatumGetCString(textInitVal);
	initVal = OidInputFunctionCall(typinput, strInitVal,
								   typioparam, -1);
	pfree(strInitVal);
	return initVal;
}

/*
 * find_compatible_peragg - search for a previously initialized per-Agg struct
 *
 * Searches the previously looked at aggregates to find one which is compatible
 * with this one, with the same input parameters. If no compatible aggregate
 * can be found, returns -1.
 *
 * As a side-effect, this also collects a list of existing per-Trans structs
 * with matching inputs. If no identical Aggref is found, the list is passed
 * later to find_compatible_perstate, to see if we can at least reuse the
 * state value of another aggregate.
 */
static int
find_compatible_peragg(Aggref *newagg, AggState *aggstate,
					   int lastaggno, List **same_input_transnos)
{
	int			aggno;
	AggStatePerAgg peraggs;

	*same_input_transnos = NIL;

	/* we mustn't reuse the aggref if it contains volatile function calls */
	if (contain_volatile_functions((Node *) newagg))
		return -1;

	peraggs = aggstate->peragg;

	/*
	 * Search through the list of already seen aggregates. If we find an
	 * existing aggregate with the same aggregate function and input
	 * parameters as an existing one, then we can re-use that one. While
	 * searching, we'll also collect a list of Aggrefs with the same input
	 * parameters. If no matching Aggref is found, the caller can potentially
	 * still re-use the transition state of one of them.
	 */
	for (aggno = 0; aggno <= lastaggno; aggno++)
	{
		AggStatePerAgg peragg;
		Aggref	   *existingRef;

		peragg = &peraggs[aggno];
		existingRef = peragg->aggref;

		/* all of the following must be the same or it's no match */
		if (newagg->inputcollid != existingRef->inputcollid ||
			newagg->aggtranstype != existingRef->aggtranstype ||
			newagg->aggstar != existingRef->aggstar ||
			newagg->aggvariadic != existingRef->aggvariadic ||
			newagg->aggkind != existingRef->aggkind ||
			!equal(newagg->aggdirectargs, existingRef->aggdirectargs) ||
			!equal(newagg->args, existingRef->args) ||
			!equal(newagg->aggorder, existingRef->aggorder) ||
			!equal(newagg->aggdistinct, existingRef->aggdistinct) ||
			!equal(newagg->aggfilter, existingRef->aggfilter))
			continue;

		/* if it's the same aggregate function then report exact match */
		if (newagg->aggfnoid == existingRef->aggfnoid &&
			newagg->aggtype == existingRef->aggtype &&
			newagg->aggcollid == existingRef->aggcollid)
		{
			list_free(*same_input_transnos);
			*same_input_transnos = NIL;
			return aggno;
		}

		/*
		 * Not identical, but it had the same inputs. Return it to the caller,
		 * in case we can re-use its per-trans state.
		 */
		*same_input_transnos = lappend_int(*same_input_transnos,
										   peragg->transno);
	}

	return -1;
}

/*
 * find_compatible_pertrans - search for a previously initialized per-Trans
 * struct
 *
 * Searches the list of transnos for a per-Trans struct with the same
 * transition state and initial condition. (The inputs have already been
 * verified to match.)
 */
static int
find_compatible_pertrans(AggState *aggstate, Aggref *newagg,
						 Oid aggtransfn, Oid aggtranstype,
						 Oid aggserialfn, Oid aggdeserialfn,
						 Datum initValue, bool initValueIsNull,
						 List *transnos)
{
	ListCell   *lc;

	foreach(lc, transnos)
	{
		int			transno = lfirst_int(lc);
		AggStatePerTrans pertrans = &aggstate->pertrans[transno];

		/*
		 * if the transfns or transition state types are not the same then the
		 * state can't be shared.
		 */
		if (aggtransfn != pertrans->transfn_oid ||
			aggtranstype != pertrans->aggtranstype)
			continue;

		/*
		 * The serialization and deserialization functions must match, if
		 * present, as we're unable to share the trans state for aggregates
		 * which will serialize or deserialize into different formats.
		 * Remember that these will be InvalidOid if they're not required for
		 * this agg node.
		 */
		if (aggserialfn != pertrans->serialfn_oid ||
			aggdeserialfn != pertrans->deserialfn_oid)
			continue;

		/* Check that the initial condition matches, too. */
		if (initValueIsNull && pertrans->initValueIsNull)
			return transno;

		if (!initValueIsNull && !pertrans->initValueIsNull &&
			datumIsEqual(initValue, pertrans->initValue,
						 pertrans->transtypeByVal, pertrans->transtypeLen))
		{
			return transno;
		}
	}
	return -1;
}

void
ExecEndAgg(AggState *node)
{
	PlanState  *outerPlan;
	int			transno;
	int			numGroupingSets = Max(node->maxsets, 1);
	int			setno;

	/* Make sure we have closed any open tuplesorts */

	if (node->sort_in)
		tuplesort_end(node->sort_in);
	if (node->sort_out)
		tuplesort_end(node->sort_out);

	for (transno = 0; transno < node->numtrans; transno++)
	{
		AggStatePerTrans pertrans = &node->pertrans[transno];

		for (setno = 0; setno < numGroupingSets; setno++)
		{
			if (pertrans->sortstates[setno])
				tuplesort_end(pertrans->sortstates[setno]);
		}
	}

	/* And ensure any agg shutdown callbacks have been called */
	for (setno = 0; setno < numGroupingSets; setno++)
		ReScanExprContext(node->aggcontexts[setno]);

	/*
	 * We don't actually free any ExprContexts here (see comment in
	 * ExecFreeExprContext), just unlinking the output one from the plan node
	 * suffices.
	 */
	ExecFreeExprContext(&node->ss.ps);

	/* clean up tuple table */
	ExecClearTuple(node->ss.ss_ScanTupleSlot);

	outerPlan = outerPlanState(node);
	ExecEndNode(outerPlan);
}

void
ExecReScanAgg(AggState *node)
{
	ExprContext *econtext = node->ss.ps.ps_ExprContext;
	PlanState  *outerPlan = outerPlanState(node);
	Agg		   *aggnode = (Agg *) node->ss.ps.plan;
	int			transno;
	int			numGroupingSets = Max(node->maxsets, 1);
	int			setno;

	node->agg_done = false;

	node->ss.ps.ps_TupFromTlist = false;

	if (aggnode->aggstrategy == AGG_HASHED)
	{
		/*
		 * In the hashed case, if we haven't yet built the hash table then we
		 * can just return; nothing done yet, so nothing to undo. If subnode's
		 * chgParam is not NULL then it will be re-scanned by ExecProcNode,
		 * else no reason to re-scan it at all.
		 */
		if (!node->table_filled)
			return;

		/*
		 * If we do have the hash table and the subplan does not have any
		 * parameter changes, then we can just rescan the existing hash table;
		 * no need to build it again.
		 */
		if (outerPlan->chgParam == NULL)
		{
			ResetTupleHashIterator(node->hashtable, &node->hashiter);
			return;
		}
	}

	/* Make sure we have closed any open tuplesorts */
	for (transno = 0; transno < node->numtrans; transno++)
	{
		for (setno = 0; setno < numGroupingSets; setno++)
		{
			AggStatePerTrans pertrans = &node->pertrans[transno];

			if (pertrans->sortstates[setno])
			{
				tuplesort_end(pertrans->sortstates[setno]);
				pertrans->sortstates[setno] = NULL;
			}
		}
	}

	/*
	 * We don't need to ReScanExprContext the output tuple context here;
	 * ExecReScan already did it. But we do need to reset our per-grouping-set
	 * contexts, which may have transvalues stored in them. (We use rescan
	 * rather than just reset because transfns may have registered callbacks
	 * that need to be run now.)
	 *
	 * Note that with AGG_HASHED, the hash table is allocated in a sub-context
	 * of the aggcontext. This used to be an issue, but now, resetting a
	 * context automatically deletes sub-contexts too.
	 */

	for (setno = 0; setno < numGroupingSets; setno++)
	{
		ReScanExprContext(node->aggcontexts[setno]);
	}

	/* Release first tuple of group, if we have made a copy */
	if (node->grp_firstTuple != NULL)
	{
		heap_freetuple(node->grp_firstTuple);
		node->grp_firstTuple = NULL;
	}
	ExecClearTuple(node->ss.ss_ScanTupleSlot);

	/* Forget current agg values */
	MemSet(econtext->ecxt_aggvalues, 0, sizeof(Datum) * node->numaggs);
	MemSet(econtext->ecxt_aggnulls, 0, sizeof(bool) * node->numaggs);

	if (aggnode->aggstrategy == AGG_HASHED)
	{
		/* Rebuild an empty hash table */
		build_hash_table(node);
		node->table_filled = false;
	}
	else
	{
		/*
		 * Reset the per-group state (in particular, mark transvalues null)
		 */
		MemSet(node->pergroup, 0,
			 sizeof(AggStatePerGroupData) * node->numaggs * numGroupingSets);

		/* reset to phase 0 */
		initialize_phase(node, 0);

		node->input_done = false;
		node->projected_set = -1;
	}

	if (outerPlan->chgParam == NULL)
		ExecReScan(outerPlan);
}


/***********************************************************************
 * API exposed to aggregate functions
 ***********************************************************************/


/*
 * AggCheckCallContext - test if a SQL function is being called as an aggregate
 *
 * The transition and/or final functions of an aggregate may want to verify
 * that they are being called as aggregates, rather than as plain SQL
 * functions.  They should use this function to do so.  The return value
 * is nonzero if being called as an aggregate, or zero if not.  (Specific
 * nonzero values are AGG_CONTEXT_AGGREGATE or AGG_CONTEXT_WINDOW, but more
 * values could conceivably appear in future.)
 *
 * If aggcontext isn't NULL, the function also stores at *aggcontext the
 * identity of the memory context that aggregate transition values are being
 * stored in.  Note that the same aggregate call site (flinfo) may be called
 * interleaved on different transition values in different contexts, so it's
 * not kosher to cache aggcontext under fn_extra.  It is, however, kosher to
 * cache it in the transvalue itself (for internal-type transvalues).
 */
int
AggCheckCallContext(FunctionCallInfo fcinfo, MemoryContext *aggcontext)
{
	if (fcinfo->context && IsA(fcinfo->context, AggState))
	{
		if (aggcontext)
		{
			AggState   *aggstate = ((AggState *) fcinfo->context);
			ExprContext *cxt = aggstate->aggcontexts[aggstate->current_set];

			*aggcontext = cxt->ecxt_per_tuple_memory;
		}
		return AGG_CONTEXT_AGGREGATE;
	}
	if (fcinfo->context && IsA(fcinfo->context, WindowAggState))
	{
		if (aggcontext)
			*aggcontext = ((WindowAggState *) fcinfo->context)->curaggcontext;
		return AGG_CONTEXT_WINDOW;
	}

	/* this is just to prevent "uninitialized variable" warnings */
	if (aggcontext)
		*aggcontext = NULL;
	return 0;
}

/*
 * AggGetAggref - allow an aggregate support function to get its Aggref
 *
 * If the function is being called as an aggregate support function,
 * return the Aggref node for the aggregate call.  Otherwise, return NULL.
 *
 * Note that if an aggregate is being used as a window function, this will
 * return NULL.  We could provide a similar function to return the relevant
 * WindowFunc node in such cases, but it's not needed yet.
 */
Aggref *
AggGetAggref(FunctionCallInfo fcinfo)
{
	if (fcinfo->context && IsA(fcinfo->context, AggState))
	{
		AggStatePerTrans curpertrans;

		curpertrans = ((AggState *) fcinfo->context)->curpertrans;

		if (curpertrans)
			return curpertrans->aggref;
	}
	return NULL;
}

/*
 * AggGetTempMemoryContext - fetch short-term memory context for aggregates
 *
 * This is useful in agg final functions; the context returned is one that
 * the final function can safely reset as desired.  This isn't useful for
 * transition functions, since the context returned MAY (we don't promise)
 * be the same as the context those are called in.
 *
 * As above, this is currently not useful for aggs called as window functions.
 */
MemoryContext
AggGetTempMemoryContext(FunctionCallInfo fcinfo)
{
	if (fcinfo->context && IsA(fcinfo->context, AggState))
	{
		AggState   *aggstate = (AggState *) fcinfo->context;

		return aggstate->tmpcontext->ecxt_per_tuple_memory;
	}
	return NULL;
}

/*
 * AggRegisterCallback - register a cleanup callback for an aggregate
 *
 * This is useful for aggs to register shutdown callbacks, which will ensure
 * that non-memory resources are freed.  The callback will occur just before
 * the associated aggcontext (as returned by AggCheckCallContext) is reset,
 * either between groups or as a result of rescanning the query.  The callback
 * will NOT be called on error paths.  The typical use-case is for freeing of
 * tuplestores or tuplesorts maintained in aggcontext, or pins held by slots
 * created by the agg functions.  (The callback will not be called until after
 * the result of the finalfn is no longer needed, so it's safe for the finalfn
 * to return data that will be freed by the callback.)
 *
 * As above, this is currently not useful for aggs called as window functions.
 */
void
AggRegisterCallback(FunctionCallInfo fcinfo,
					ExprContextCallbackFunction func,
					Datum arg)
{
	if (fcinfo->context && IsA(fcinfo->context, AggState))
	{
		AggState   *aggstate = (AggState *) fcinfo->context;
		ExprContext *cxt = aggstate->aggcontexts[aggstate->current_set];

		RegisterExprContextCallback(cxt, func, arg);

		return;
	}
	elog(ERROR, "aggregate function cannot register a callback in this context");
}


/*
 * aggregate_dummy - dummy execution routine for aggregate functions
 *
 * This function is listed as the implementation (prosrc field) of pg_proc
 * entries for aggregate functions.  Its only purpose is to throw an error
 * if someone mistakenly executes such a function in the normal way.
 *
 * Perhaps someday we could assign real meaning to the prosrc field of
 * an aggregate?
 */
Datum
aggregate_dummy(PG_FUNCTION_ARGS)
{
	elog(ERROR, "aggregate function %u called as normal function",
		 fcinfo->flinfo->fn_oid);
	return (Datum) 0;			/* keep compiler quiet */
}
