/*-------------------------------------------------------------------------
 *
 * nodeIndexscan.c
 *	  Routines to support indexes and indexed scans of relations
 *
 * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeIndexscan.c,v 1.49 2000/04/12 17:15:09 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *		ExecInsertIndexTuples	inserts tuples into indices on result relation
 *
 *		ExecIndexScan			scans a relation using indices
 *		ExecIndexNext			using index to retrieve next tuple
 *		ExecInitIndexScan		creates and initializes state info.
 *		ExecIndexReScan			rescans the indexed relation.
 *		ExecEndIndexScan		releases all storage.
 *		ExecIndexMarkPos		marks scan position.
 *		ExecIndexRestrPos		restores scan position.
 *
 *	 NOTES
 *		the code supporting ExecInsertIndexTuples should be
 *		collected and merged with the genam stuff.
 *
 */
#include "postgres.h"



#include "access/genam.h"
#include "access/heapam.h"
#include "executor/execdebug.h"
#include "executor/executor.h"
#include "executor/nodeIndexscan.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "parser/parsetree.h"

/* ----------------
 *		Misc stuff to move to executor.h soon -cim 6/5/90
 * ----------------
 */
#define NO_OP			0
#define LEFT_OP			1
#define RIGHT_OP		2

static TupleTableSlot *IndexNext(IndexScan *node);

/* ----------------------------------------------------------------
 *		IndexNext
 *
 *		Retrieve a tuple from the IndexScan node's currentRelation
 *		using the indices in the IndexScanState information.
 *
 *		note: the old code mentions 'Primary indices'.	to my knowledge
 *		we only support a single secondary index. -cim 9/11/89
 *
 * old comments:
 *		retrieve a tuple from relation using the indices given.
 *		The indices are used in the order they appear in 'indices'.
 *		The indices may be primary or secondary indices:
 *		  * primary index --	scan the relation 'relID' using keys supplied.
 *		  * secondary index --	scan the index relation to get the 'tid' for
 *								a tuple in the relation 'relID'.
 *		If the current index(pointed by 'indexPtr') fails to return a
 *		tuple, the next index in the indices is used.
 *
 *		  bug fix so that it should retrieve on a null scan key.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
IndexNext(IndexScan *node)
{
	EState	   *estate;
	CommonScanState *scanstate;
	IndexScanState *indexstate;
	ScanDirection direction;
	Snapshot	snapshot;
	IndexScanDescPtr scanDescs;
	IndexScanDesc scandesc;
	Relation	heapRelation;
	RetrieveIndexResult result;
	HeapTuple	tuple;
	TupleTableSlot *slot;
	Buffer		buffer = InvalidBuffer;
	int			numIndices;

	bool		bBackward;
	int			indexNumber;

	/* ----------------
	 *	extract necessary information from index scan node
	 * ----------------
	 */
	estate = node->scan.plan.state;
	direction = estate->es_direction;
	if (ScanDirectionIsBackward(node->indxorderdir))
	{
		if (ScanDirectionIsForward(direction))
			direction = BackwardScanDirection;
		else if (ScanDirectionIsBackward(direction))
			direction = ForwardScanDirection;
	}
	snapshot = estate->es_snapshot;
	scanstate = node->scan.scanstate;
	indexstate = node->indxstate;
	scanDescs = indexstate->iss_ScanDescs;
	heapRelation = scanstate->css_currentRelation;
	numIndices = indexstate->iss_NumIndices;
	slot = scanstate->css_ScanTupleSlot;

	/*
	 * Check if we are evaluating PlanQual for tuple of this relation.
	 * Additional checking is not good, but no other way for now. We could
	 * introduce new nodes for this case and handle IndexScan --> NewNode
	 * switching in Init/ReScan plan...
	 */
	if (estate->es_evTuple != NULL &&
		estate->es_evTuple[node->scan.scanrelid - 1] != NULL)
	{
		List	   *qual;

		ExecClearTuple(slot);
		if (estate->es_evTupleNull[node->scan.scanrelid - 1])
			return slot;		/* return empty slot */

		/* probably ought to use ExecStoreTuple here... */
		slot->val = estate->es_evTuple[node->scan.scanrelid - 1];
		slot->ttc_shouldFree = false;

		scanstate->cstate.cs_ExprContext->ecxt_scantuple = slot;

		/* Does the tuple meet any of the OR'd indxqual conditions? */
		foreach(qual, node->indxqualorig)
		{
			if (ExecQual((List *) lfirst(qual),
						 scanstate->cstate.cs_ExprContext,
						 false))
				break;
		}
		if (qual == NIL)		/* would not be returned by indices */
			slot->val = NULL;

		/* Flag for the next call that no more tuples */
		estate->es_evTupleNull[node->scan.scanrelid - 1] = true;

		return slot;
	}

	tuple = &(indexstate->iss_htup);

	/* ----------------
	 *	ok, now that we have what we need, fetch an index tuple.
	 *	if scanning this index succeeded then return the
	 *	appropriate heap tuple.. else return NULL.
	 * ----------------
	 */
	bBackward = ScanDirectionIsBackward(direction);
	if (bBackward)
	{
		indexNumber = numIndices - indexstate->iss_IndexPtr - 1;
		if (indexNumber < 0)
		{
			indexNumber = 0;
			indexstate->iss_IndexPtr = numIndices - 1;
		}
	}
	else
	{
		if ((indexNumber = indexstate->iss_IndexPtr) < 0)
		{
			indexNumber = 0;
			indexstate->iss_IndexPtr = 0;
		}
	}
	while (indexNumber < numIndices)
	{
		scandesc = scanDescs[indexstate->iss_IndexPtr];
		while ((result = index_getnext(scandesc, direction)) != NULL)
		{
			tuple->t_self = result->heap_iptr;
			heap_fetch(heapRelation, snapshot, tuple, &buffer);
			pfree(result);

			if (tuple->t_data != NULL)
			{
				bool		prev_matches = false;
				int			prev_index;
				List	   *qual;

				/*
				 * store the scanned tuple in the scan tuple slot of the
				 * scan state.	Eventually we will only do this and not
				 * return a tuple.	Note: we pass 'false' because tuples
				 * returned by amgetnext are pointers onto disk pages and
				 * must not be pfree()'d.
				 */
				ExecStoreTuple(tuple,	/* tuple to store */
							   slot,	/* slot to store in */
							   buffer,	/* buffer associated with tuple  */
							   false);	/* don't pfree */

				/*
				 * At this point we have an extra pin on the buffer,
				 * because ExecStoreTuple incremented the pin count. Drop
				 * our local pin.
				 */
				ReleaseBuffer(buffer);

				/*
				 * We must check to see if the current tuple was already
				 * matched by an earlier index, so we don't double-report
				 * it. We do this by passing the tuple through ExecQual
				 * and checking for failure with all previous
				 * qualifications.
				 */
				scanstate->cstate.cs_ExprContext->ecxt_scantuple = slot;
				qual = node->indxqualorig;
				for (prev_index = 0; prev_index < indexstate->iss_IndexPtr;
					 prev_index++)
				{
					if (ExecQual((List *) lfirst(qual),
								 scanstate->cstate.cs_ExprContext,
								 false))
					{
						prev_matches = true;
						break;
					}
					qual = lnext(qual);
				}
				if (!prev_matches)
					return slot;/* OK to return tuple */
				/* Duplicate tuple, so drop it and loop back for another */
				ExecClearTuple(slot);
			}
		}
		if (indexNumber < numIndices)
		{
			indexNumber++;
			if (bBackward)
				indexstate->iss_IndexPtr--;
			else
				indexstate->iss_IndexPtr++;
		}
	}
	/* ----------------
	 *	if we get here it means the index scan failed so we
	 *	are at the end of the scan..
	 * ----------------
	 */
	return ExecClearTuple(slot);
}

/* ----------------------------------------------------------------
 *		ExecIndexScan(node)
 *
 * old comments:
 *		Scans the relation using primary or secondary indices and returns
 *		   the next qualifying tuple in the direction specified.
 *		It calls ExecScan() and passes it the access methods which returns
 *		the next tuple using the indices.
 *
 *		Conditions:
 *		  -- the "cursor" maintained by the AMI is positioned at the tuple
 *			 returned previously.
 *
 *		Initial States:
 *		  -- the relation indicated is opened for scanning so that the
 *			 "cursor" is positioned before the first qualifying tuple.
 *		  -- all index realtions are opened for scanning.
 *		  -- indexPtr points to the first index.
 *		  -- state variable ruleFlag = nil.
 * ----------------------------------------------------------------
 */
TupleTableSlot *
ExecIndexScan(IndexScan *node)
{
	/* ----------------
	 *	use IndexNext as access method
	 * ----------------
	 */
	return ExecScan(&node->scan, IndexNext);
}

/* ----------------------------------------------------------------
 *		ExecIndexReScan(node)
 *
 *		Recalculates the value of the scan keys whose value depends on
 *		information known at runtime and rescans the indexed relation.
 *		Updating the scan key was formerly done separately in
 *		ExecUpdateIndexScanKeys. Integrating it into ReScan
 *		makes rescans of indices and
 *		relations/general streams more uniform.
 *
 * ----------------------------------------------------------------
 */
void
ExecIndexReScan(IndexScan *node, ExprContext *exprCtxt, Plan *parent)
{
	EState	   *estate;
	IndexScanState *indexstate;
	ScanDirection direction;
	IndexScanDescPtr scanDescs;
	ScanKey    *scanKeys;
	IndexScanDesc scan;
	ScanKey		skey;
	int			numIndices;
	int			i;

	Pointer    *runtimeKeyInfo;
	int		   *numScanKeys;
	List	   *indxqual;
	List	   *qual;
	int			n_keys;
	ScanKey		scan_keys;
	int		   *run_keys;
	int			j;
	Expr	   *clause;
	Node	   *scanexpr;
	Datum		scanvalue;
	bool		isNull;
	bool		isDone;

	indexstate = node->indxstate;
	estate = node->scan.plan.state;
	direction = estate->es_direction;
	numIndices = indexstate->iss_NumIndices;
	scanDescs = indexstate->iss_ScanDescs;
	scanKeys = indexstate->iss_ScanKeys;
	runtimeKeyInfo = (Pointer *) indexstate->iss_RuntimeKeyInfo;
	numScanKeys = indexstate->iss_NumScanKeys;
	indexstate->iss_IndexPtr = -1;
	if (ScanDirectionIsBackward(node->indxorderdir))
		indexstate->iss_IndexPtr = numIndices;

	/* If we are being passed an outer tuple, save it for runtime key calc */
	if (exprCtxt != NULL)
		node->scan.scanstate->cstate.cs_ExprContext->ecxt_outertuple =
			exprCtxt->ecxt_outertuple;

	/* If this is re-scanning of PlanQual ... */
	if (estate->es_evTuple != NULL &&
		estate->es_evTuple[node->scan.scanrelid - 1] != NULL)
	{
		estate->es_evTupleNull[node->scan.scanrelid - 1] = false;
		return;
	}

	/*
	 * get the index qualifications and recalculate the appropriate values
	 */
	indxqual = node->indxqual;
	for (i = 0; i < numIndices; i++)
	{
		qual = lfirst(indxqual);
		indxqual = lnext(indxqual);
		n_keys = numScanKeys[i];
		scan_keys = (ScanKey) scanKeys[i];

		if (runtimeKeyInfo)
		{
			run_keys = (int *) runtimeKeyInfo[i];
			for (j = 0; j < n_keys; j++)
			{

				/*
				 * If we have a run-time key, then extract the run-time
				 * expression and evaluate it with respect to the current
				 * outer tuple.  We then stick the result into the scan
				 * key.
				 */
				if (run_keys[j] != NO_OP)
				{
					clause = nth(j, qual);
					scanexpr = (run_keys[j] == RIGHT_OP) ?
						(Node *) get_rightop(clause) :
						(Node *) get_leftop(clause);

					/*
					 * pass in isDone but ignore it.  We don't iterate in
					 * quals
					 */
					scanvalue = (Datum)
						ExecEvalExpr(scanexpr,
							 node->scan.scanstate->cstate.cs_ExprContext,
									 &isNull, &isDone);
					scan_keys[j].sk_argument = scanvalue;
					if (isNull)
						scan_keys[j].sk_flags |= SK_ISNULL;
					else
						scan_keys[j].sk_flags &= ~SK_ISNULL;
				}
			}
		}
		scan = scanDescs[i];
		skey = scanKeys[i];
		index_rescan(scan, direction, skey);
	}
	/* ----------------
	 *	perhaps return something meaningful
	 * ----------------
	 */
	return;
}

/* ----------------------------------------------------------------
 *		ExecEndIndexScan
 *
 * old comments
 *		Releases any storage allocated through C routines.
 *		Returns nothing.
 * ----------------------------------------------------------------
 */
void
ExecEndIndexScan(IndexScan *node)
{
	CommonScanState *scanstate;
	IndexScanState *indexstate;
	Pointer    *runtimeKeyInfo;
	ScanKey    *scanKeys;
	List	   *indxqual;
	int		   *numScanKeys;
	int			numIndices;
	int			i;

	scanstate = node->scan.scanstate;
	indexstate = node->indxstate;
	indxqual = node->indxqual;
	runtimeKeyInfo = (Pointer *) indexstate->iss_RuntimeKeyInfo;

	/* ----------------
	 *	extract information from the node
	 * ----------------
	 */
	numIndices = indexstate->iss_NumIndices;
	scanKeys = indexstate->iss_ScanKeys;
	numScanKeys = indexstate->iss_NumScanKeys;

	/* ----------------
	 *	Free the projection info and the scan attribute info
	 *
	 *	Note: we don't ExecFreeResultType(scanstate)
	 *		  because the rule manager depends on the tupType
	 *		  returned by ExecMain().  So for now, this
	 *		  is freed at end-transaction time.  -cim 6/2/91
	 * ----------------
	 */
	ExecFreeProjectionInfo(&scanstate->cstate);

	/* ----------------
	 *	close the heap and index relations
	 * ----------------
	 */
	ExecCloseR((Plan *) node);

	/* ----------------
	 *	free the scan keys used in scanning the indices
	 * ----------------
	 */
	for (i = 0; i < numIndices; i++)
	{
		if (scanKeys[i] != NULL)
			pfree(scanKeys[i]);
	}
	pfree(scanKeys);
	pfree(numScanKeys);

	if (runtimeKeyInfo)
	{
		for (i = 0; i < numIndices; i++)
		{
			List	   *qual;
			int			n_keys;

			qual = nth(i, indxqual);
			n_keys = length(qual);
			if (n_keys > 0)
				pfree(runtimeKeyInfo[i]);
		}
		pfree(runtimeKeyInfo);
	}

	/* ----------------
	 *	clear out tuple table slots
	 * ----------------
	 */
	ExecClearTuple(scanstate->cstate.cs_ResultTupleSlot);
	ExecClearTuple(scanstate->css_ScanTupleSlot);
/*	  ExecClearTuple(scanstate->css_RawTupleSlot); */
}

/* ----------------------------------------------------------------
 *		ExecIndexMarkPos
 *
 * old comments
 *		Marks scan position by marking the current index.
 *		Returns nothing.
 * ----------------------------------------------------------------
 */
void
ExecIndexMarkPos(IndexScan *node)
{
	IndexScanState *indexstate;
	IndexScanDescPtr indexScanDescs;
	IndexScanDesc scanDesc;
	int			indexPtr;

	indexstate = node->indxstate;
	indexPtr = indexstate->iss_MarkIndexPtr = indexstate->iss_IndexPtr;
	indexScanDescs = indexstate->iss_ScanDescs;
	scanDesc = indexScanDescs[indexPtr];

#ifdef NOT_USED
	IndexScanMarkPosition(scanDesc);
#endif
	index_markpos(scanDesc);
}

/* ----------------------------------------------------------------
 *		ExecIndexRestrPos
 *
 * old comments
 *		Restores scan position by restoring the current index.
 *		Returns nothing.
 *
 *		XXX Assumes previously marked scan position belongs to current index
 * ----------------------------------------------------------------
 */
void
ExecIndexRestrPos(IndexScan *node)
{
	IndexScanState *indexstate;
	IndexScanDescPtr indexScanDescs;
	IndexScanDesc scanDesc;
	int			indexPtr;

	indexstate = node->indxstate;
	indexPtr = indexstate->iss_IndexPtr = indexstate->iss_MarkIndexPtr;
	indexScanDescs = indexstate->iss_ScanDescs;
	scanDesc = indexScanDescs[indexPtr];

#ifdef NOT_USED
	IndexScanRestorePosition(scanDesc);
#endif
	index_restrpos(scanDesc);
}

/* ----------------------------------------------------------------
 *		ExecInitIndexScan
  *
 *		Initializes the index scan's state information, creates
 *		scan keys, and opens the base and index relations.
 *
 *		Note: index scans have 2 sets of state information because
 *			  we have to keep track of the base relation and the
 *			  index relations.
 *
 * old comments
 *		Creates the run-time state information for the node and
 *		sets the relation id to contain relevant decriptors.
 *
 *		Parameters:
 *		  node: IndexNode node produced by the planner.
 *		  estate: the execution state initialized in InitPlan.
 * ----------------------------------------------------------------
 */
bool
ExecInitIndexScan(IndexScan *node, EState *estate, Plan *parent)
{
	IndexScanState *indexstate;
	CommonScanState *scanstate;
	List	   *indxqual;
	List	   *indxid;
	int			i;
	int			numIndices;
	int			indexPtr;
	ScanKey    *scanKeys;
	int		   *numScanKeys;
	RelationPtr relationDescs;
	IndexScanDescPtr scanDescs;
	Pointer    *runtimeKeyInfo;
	bool		have_runtime_keys;
	List	   *rangeTable;
	RangeTblEntry *rtentry;
	Index		relid;
	Oid			reloid;

	Relation	currentRelation;
	HeapScanDesc currentScanDesc;
	ScanDirection direction;
	int			baseid;

	List	   *execParam = NULL;

	/* ----------------
	 *	assign execution state to node
	 * ----------------
	 */
	node->scan.plan.state = estate;

	/* --------------------------------
	 *	Part 1)  initialize scan state
	 *
	 *	create new CommonScanState for node
	 * --------------------------------
	 */
	scanstate = makeNode(CommonScanState);
/*
	scanstate->ss_ProcOuterFlag = false;
	scanstate->ss_OldRelId = 0;
*/

	node->scan.scanstate = scanstate;

	/* ----------------
	 *	assign node's base_id .. we don't use AssignNodeBaseid() because
	 *	the increment is done later on after we assign the index scan's
	 *	scanstate.	see below.
	 * ----------------
	 */
	baseid = estate->es_BaseId;
/*	  scanstate->csstate.cstate.bnode.base_id = baseid; */
	scanstate->cstate.cs_base_id = baseid;

	/* ----------------
	 *	create expression context for node
	 * ----------------
	 */
	ExecAssignExprContext(estate, &scanstate->cstate);

#define INDEXSCAN_NSLOTS 3
	/* ----------------
	 *	tuple table initialization
	 * ----------------
	 */
	ExecInitResultTupleSlot(estate, &scanstate->cstate);
	ExecInitScanTupleSlot(estate, scanstate);
/*	  ExecInitRawTupleSlot(estate, scanstate); */

	/* ----------------
	 *	initialize projection info.  result type comes from scan desc
	 *	below..
	 * ----------------
	 */
	ExecAssignProjectionInfo((Plan *) node, &scanstate->cstate);

	/* --------------------------------
	  *  Part 2)  initialize index scan state
	  *
	  *  create new IndexScanState for node
	  * --------------------------------
	  */
	indexstate = makeNode(IndexScanState);
	indexstate->iss_NumIndices = 0;
	indexstate->iss_IndexPtr = -1;
	indexstate->iss_ScanKeys = NULL;
	indexstate->iss_NumScanKeys = NULL;
	indexstate->iss_RuntimeKeyInfo = NULL;
	indexstate->iss_RelationDescs = NULL;
	indexstate->iss_ScanDescs = NULL;

	node->indxstate = indexstate;

	/* ----------------
	 *	assign base id to index scan state also
	 * ----------------
	 */
	indexstate->cstate.cs_base_id = baseid;
	baseid++;
	estate->es_BaseId = baseid;

	/* ----------------
	 *	get the index node information
	 * ----------------
	 */
	indxid = node->indxid;
	numIndices = length(indxid);
	indexPtr = -1;

	CXT1_printf("ExecInitIndexScan: context is %d\n", CurrentMemoryContext);

	/* ----------------
	 *	scanKeys is used to keep track of the ScanKey's. This is needed
	 *	because a single scan may use several indices and each index has
	 *	its own ScanKey.
	 * ----------------
	 */
	numScanKeys = (int *) palloc(numIndices * sizeof(int));
	scanKeys = (ScanKey *) palloc(numIndices * sizeof(ScanKey));
	relationDescs = (RelationPtr) palloc(numIndices * sizeof(Relation));
	scanDescs = (IndexScanDescPtr) palloc(numIndices * sizeof(IndexScanDesc));

	/* ----------------
	 *	initialize runtime key info.
	 * ----------------
	 */
	have_runtime_keys = false;
	runtimeKeyInfo = (Pointer *)
		palloc(numIndices * sizeof(Pointer));

	/* ----------------
	 *	build the index scan keys from the index qualification
	 * ----------------
	 */
	indxqual = node->indxqual;
	for (i = 0; i < numIndices; i++)
	{
		int			j;
		List	   *qual;
		int			n_keys;
		ScanKey		scan_keys;
		int		   *run_keys;

		qual = lfirst(indxqual);
		indxqual = lnext(indxqual);
		n_keys = length(qual);
		scan_keys = (n_keys <= 0) ? NULL :
			(ScanKey) palloc(n_keys * sizeof(ScanKeyData));
		run_keys = (n_keys <= 0) ? NULL :
			(int *) palloc(n_keys * sizeof(int));

		CXT1_printf("ExecInitIndexScan: context is %d\n", CurrentMemoryContext);

		/* ----------------
		 *	for each opclause in the given qual,
		 *	convert each qual's opclause into a single scan key
		 * ----------------
		 */
		for (j = 0; j < n_keys; j++)
		{
			Expr	   *clause; /* one part of index qual */
			Oper	   *op;		/* operator used in scan.. */
			Node	   *leftop; /* expr on lhs of operator */
			Node	   *rightop;/* expr on rhs ... */
			bits16		flags = 0;

			int			scanvar;/* which var identifies varattno */
			AttrNumber	varattno = 0;	/* att number used in scan */
			Oid			opid;	/* operator id used in scan */
			Datum		scanvalue = 0;	/* value used in scan (if const) */

			/* ----------------
			 *	extract clause information from the qualification
			 * ----------------
			 */
			clause = nth(j, qual);

			op = (Oper *) clause->oper;
			if (!IsA(clause, Expr) ||!IsA(op, Oper))
				elog(ERROR, "ExecInitIndexScan: indxqual not an opclause!");

			opid = op->opid;

			/* ----------------
			 *	Here we figure out the contents of the index qual.
			 *	The usual case is (var op const) or (const op var)
			 *	which means we form a scan key for the attribute
			 *	listed in the var node and use the value of the const.
			 *
			 *	If we don't have a const node, then it means that
			 *	one of the var nodes refers to the "scan" tuple and
			 *	is used to determine which attribute to scan, and the
			 *	other expression is used to calculate the value used in
			 *	scanning the index.
			 *
			 *	This means our index scan's scan key is a function of
			 *	information obtained during the execution of the plan
			 *	in which case we need to recalculate the index scan key
			 *	at run time.
			 *
			 *	Hence, we set have_runtime_keys to true and then set
			 *	the appropriate flag in run_keys to LEFT_OP or RIGHT_OP.
			 *	The corresponding scan keys are recomputed at run time.
			 *
			 *	XXX Although this code *thinks* it can handle an indexqual
			 *	with the indexkey on either side, in fact it cannot.
			 *	Indexscans only work with quals that have the indexkey on
			 *	the left (the planner/optimizer makes sure it never passes
			 *	anything else).  The reason: the scankey machinery has no
			 *	provision for distinguishing which side of the operator is
			 *	the indexed attribute and which is the compared-to constant.
			 *	It just assumes that the attribute is on the left :-(
			 *
			 *	I am leaving this code able to support both ways, even though
			 *	half of it is dead code, on the off chance that someone will
			 *	fix the scankey machinery someday --- tgl 8/11/99.
			 * ----------------
			 */

			scanvar = NO_OP;

			/* ----------------
			 *	determine information in leftop
			 * ----------------
			 */
			leftop = (Node *) get_leftop(clause);

			Assert(leftop != NULL);

			if (IsA(leftop, Var) &&var_is_rel((Var *) leftop))
			{
				/* ----------------
				 *	if the leftop is a "rel-var", then it means
				 *	that it is a var node which tells us which
				 *	attribute to use for our scan key.
				 * ----------------
				 */
				varattno = ((Var *) leftop)->varattno;
				scanvar = LEFT_OP;
			}
			else if (is_funcclause(leftop) &&
					 var_is_rel(lfirst(((Expr *) leftop)->args)))
			{
				/* ----------------
				 *	if the leftop is a func node then it means
				 *	it identifies the value to place in our scan key.
				 *	Since functional indices have only one attribute
				 *	the attno must always be set to 1.
				 * ----------------
				 */
				varattno = 1;
				scanvar = LEFT_OP;
			}
			else if (IsA(leftop, Const))
			{
				/* ----------------
				 *	if the leftop is a const node then it means
				 *	it identifies the value to place in our scan key.
				 * ----------------
				 */
				run_keys[j] = NO_OP;
				scanvalue = ((Const *) leftop)->constvalue;
			}
			else if (IsA(leftop, Param))
			{
				bool		isnull;

				/* ----------------
				 *	if the leftop is a Param node then it means
				 *	it identifies the value to place in our scan key.
				 * ----------------
				 */

				/* Life was so easy before ... subselects */
				if (((Param *) leftop)->paramkind == PARAM_EXEC)
				{
					have_runtime_keys = true;
					run_keys[j] = LEFT_OP;
					execParam = lappendi(execParam, ((Param *) leftop)->paramid);
				}
				else
				{
					scanvalue = ExecEvalParam((Param *) leftop,
										scanstate->cstate.cs_ExprContext,
											  &isnull);
					if (isnull)
						flags |= SK_ISNULL;

					run_keys[j] = NO_OP;
				}
			}
			else
			{
				/* ----------------
				 *	otherwise, the leftop contains information usable
				 *	at runtime to figure out the value to place in our
				 *	scan key.
				 * ----------------
				 */
				have_runtime_keys = true;
				run_keys[j] = LEFT_OP;
				scanvalue = Int32GetDatum((int32) true);
			}

			/* ----------------
			 *	now determine information in rightop
			 * ----------------
			 */
			rightop = (Node *) get_rightop(clause);

			Assert(rightop != NULL);

			if (IsA(rightop, Var) &&var_is_rel((Var *) rightop))
			{
				/* ----------------
				 *	here we make sure only one op identifies the
				 *	scan-attribute...
				 * ----------------
				 */
				if (scanvar == LEFT_OP)
					elog(ERROR, "ExecInitIndexScan: %s",
						 "both left and right op's are rel-vars");

				/* ----------------
				 *	if the rightop is a "rel-var", then it means
				 *	that it is a var node which tells us which
				 *	attribute to use for our scan key.
				 * ----------------
				 */
				varattno = ((Var *) rightop)->varattno;
				scanvar = RIGHT_OP;
			}
			else if (is_funcclause(rightop) &&
					 var_is_rel(lfirst(((Expr *) rightop)->args)))
			{
				/* ----------------
				 *	if the rightop is a func node then it means
				 *	it identifies the value to place in our scan key.
				 *	Since functional indices have only one attribute
				 *	the attno must always be set to 1.
				 * ----------------
				 */
				if (scanvar == LEFT_OP)
					elog(ERROR, "ExecInitIndexScan: %s",
						 "both left and right ops are rel-vars");

				varattno = 1;
				scanvar = RIGHT_OP;
			}
			else if (IsA(rightop, Const))
			{
				/* ----------------
				 *	if the rightop is a const node then it means
				 *	it identifies the value to place in our scan key.
				 * ----------------
				 */
				run_keys[j] = NO_OP;
				scanvalue = ((Const *) rightop)->constvalue;
			}
			else if (IsA(rightop, Param))
			{
				bool		isnull;

				/* ----------------
				 *	if the rightop is a Param node then it means
				 *	it identifies the value to place in our scan key.
				 * ----------------
				 */

				/* Life was so easy before ... subselects */
				if (((Param *) rightop)->paramkind == PARAM_EXEC)
				{
					have_runtime_keys = true;
					run_keys[j] = RIGHT_OP;
					execParam = lappendi(execParam, ((Param *) rightop)->paramid);
				}
				else
				{
					scanvalue = ExecEvalParam((Param *) rightop,
										scanstate->cstate.cs_ExprContext,
											  &isnull);
					if (isnull)
						flags |= SK_ISNULL;

					run_keys[j] = NO_OP;
				}
			}
			else
			{
				/* ----------------
				 *	otherwise, the rightop contains information usable
				 *	at runtime to figure out the value to place in our
				 *	scan key.
				 * ----------------
				 */
				have_runtime_keys = true;
				run_keys[j] = RIGHT_OP;
				scanvalue = Int32GetDatum((int32) true);
			}

			/* ----------------
			 *	now check that at least one op tells us the scan
			 *	attribute...
			 * ----------------
			 */
			if (scanvar == NO_OP)
				elog(ERROR, "ExecInitIndexScan: %s",
					 "neither leftop nor rightop refer to scan relation");

			/* ----------------
			 *	initialize the scan key's fields appropriately
			 * ----------------
			 */
			ScanKeyEntryInitialize(&scan_keys[j],
								   flags,
								   varattno,	/* attribute number to
												 * scan */
								   (RegProcedure) opid, /* reg proc to use */
								   (Datum) scanvalue);	/* constant */
		}

		/* ----------------
		 *	store the key information into our array.
		 * ----------------
		 */
		numScanKeys[i] = n_keys;
		scanKeys[i] = scan_keys;
		runtimeKeyInfo[i] = (Pointer) run_keys;
	}

	indexstate->iss_NumIndices = numIndices;
	if (ScanDirectionIsBackward(node->indxorderdir))
		indexPtr = numIndices;
	indexstate->iss_IndexPtr = indexPtr;
	indexstate->iss_ScanKeys = scanKeys;
	indexstate->iss_NumScanKeys = numScanKeys;

	/* ----------------
	 *	If all of our keys have the form (op var const) , then we have no
	 *	runtime keys so we store NULL in the runtime key info.
	 *	Otherwise runtime key info contains an array of pointers
	 *	(one for each index) to arrays of flags (one for each key)
	 *	which indicate that the qual needs to be evaluated at runtime.
	 *	-cim 10/24/89
	 * ----------------
	 */
	if (have_runtime_keys)
		indexstate->iss_RuntimeKeyInfo = (Pointer) runtimeKeyInfo;
	else
		indexstate->iss_RuntimeKeyInfo = NULL;

	/* ----------------
	 *	get the range table and direction information
	 *	from the execution state (these are needed to
	 *	open the relations).
	 * ----------------
	 */
	rangeTable = estate->es_range_table;
	direction = estate->es_direction;

	/* ----------------
	 *	open the base relation
	 * ----------------
	 */
	relid = node->scan.scanrelid;
	rtentry = rt_fetch(relid, rangeTable);
	reloid = rtentry->relid;

	ExecOpenScanR(reloid,		/* relation */
				  0,			/* nkeys */
				  (ScanKey) NULL,		/* scan key */
				  0,			/* is index */
				  direction,	/* scan direction */
				  estate->es_snapshot,	/* */
				  &currentRelation,		/* return: rel desc */
				  (Pointer *) &currentScanDesc);		/* return: scan desc */

	if (!RelationGetForm(currentRelation)->relhasindex)
		elog(ERROR, "indexes of the relation %u was inactivated", reloid);
	scanstate->css_currentRelation = currentRelation;
	scanstate->css_currentScanDesc = currentScanDesc;


	/* ----------------
	 *	get the scan type from the relation descriptor.
	 * ----------------
	 */
	ExecAssignScanType(scanstate, RelationGetDescr(currentRelation));
	ExecAssignResultTypeFromTL((Plan *) node, &scanstate->cstate);

	/* ----------------
	 *	index scans don't have subtrees..
	 * ----------------
	 */
/*	  scanstate->ss_ProcOuterFlag = false; */

	/* ----------------
	 *	open the index relations and initialize
	 *	relation and scan descriptors.
	 * ----------------
	 */
	for (i = 0; i < numIndices; i++)
	{
		Oid			indexOid = (Oid) nthi(i, indxid);

		if (indexOid != 0)
		{
			ExecOpenScanR(indexOid,		/* relation */
						  numScanKeys[i],		/* nkeys */
						  scanKeys[i],	/* scan key */
						  true, /* is index */
						  direction,	/* scan direction */
						  estate->es_snapshot,
						  &(relationDescs[i]),	/* return: rel desc */
						  (Pointer *) &(scanDescs[i]));
			/* return: scan desc */
		}
	}

	indexstate->iss_RelationDescs = relationDescs;
	indexstate->iss_ScanDescs = scanDescs;

	indexstate->cstate.cs_TupFromTlist = false;

	/*
	 * if there are some PARAM_EXEC in skankeys then force index rescan on
	 * first scan.
	 */
	((Plan *) node)->chgParam = execParam;

	/* ----------------
	 *	all done.
	 * ----------------
	 */
	return TRUE;
}

int
ExecCountSlotsIndexScan(IndexScan *node)
{
	return ExecCountSlotsNode(outerPlan((Plan *) node)) +
	ExecCountSlotsNode(innerPlan((Plan *) node)) + INDEXSCAN_NSLOTS;
}
