Fix LookupTupleHashEntryHash() pipeline-stall issue.

Refactor hash lookups in nodeAgg.c to improve performance.

Author: Andres Freund and Jeff Davis
Discussion: https://postgr.es/m/20200612213715.op4ye4q7gktqvpuo%40alap3.anarazel.de
Backpatch-through: 13

src/backend/executor/execGrouping.c

@@ -22,11 +22,11 @@
 #include "utils/memutils.h"
 
 static int	TupleHashTableMatch(struct tuplehash_hash *tb, const MinimalTuple tuple1, const MinimalTuple tuple2);
-static uint32 TupleHashTableHash_internal(struct tuplehash_hash *tb,
-										  const MinimalTuple tuple);
-static TupleHashEntry LookupTupleHashEntry_internal(TupleHashTable hashtable,
-													TupleTableSlot *slot,
-													bool *isnew, uint32 hash);
+static inline uint32 TupleHashTableHash_internal(struct tuplehash_hash *tb,
+												 const MinimalTuple tuple);
+static inline TupleHashEntry LookupTupleHashEntry_internal(TupleHashTable hashtable,
+														   TupleTableSlot *slot,
+														   bool *isnew, uint32 hash);
 
 /*
  * Define parameters for tuple hash table code generation. The interface is
@@ -291,6 +291,9 @@ ResetTupleHashTable(TupleHashTable hashtable)
  * If isnew is NULL, we do not create new entries; we return NULL if no
  * match is found.
  *
+ * If hash is not NULL, we set it to the calculated hash value. This allows
+ * callers access to the hash value even if no entry is returned.
+ *
  * If isnew isn't NULL, then a new entry is created if no existing entry
  * matches.  On return, *isnew is true if the entry is newly created,
  * false if it existed already.  ->additional_data in the new entry has
@@ -298,11 +301,11 @@ ResetTupleHashTable(TupleHashTable hashtable)
  */
 TupleHashEntry
 LookupTupleHashEntry(TupleHashTable hashtable, TupleTableSlot *slot,
-					 bool *isnew)
+					 bool *isnew, uint32 *hash)
 {
 	TupleHashEntry entry;
 	MemoryContext oldContext;
-	uint32		hash;
+	uint32		local_hash;
 
 	/* Need to run the hash functions in short-lived context */
 	oldContext = MemoryContextSwitchTo(hashtable->tempcxt);
@@ -312,8 +315,13 @@ LookupTupleHashEntry(TupleHashTable hashtable, TupleTableSlot *slot,
 	hashtable->in_hash_funcs = hashtable->tab_hash_funcs;
 	hashtable->cur_eq_func = hashtable->tab_eq_func;
 
-	hash = TupleHashTableHash_internal(hashtable->hashtab, NULL);
-	entry = LookupTupleHashEntry_internal(hashtable, slot, isnew, hash);
+	local_hash = TupleHashTableHash_internal(hashtable->hashtab, NULL);
+	entry = LookupTupleHashEntry_internal(hashtable, slot, isnew, local_hash);
+
+	if (hash != NULL)
+		*hash = local_hash;
+
+	Assert(entry == NULL || entry->hash == local_hash);
 
 	MemoryContextSwitchTo(oldContext);
 
@@ -362,6 +370,7 @@ LookupTupleHashEntryHash(TupleHashTable hashtable, TupleTableSlot *slot,
 	hashtable->cur_eq_func = hashtable->tab_eq_func;
 
 	entry = LookupTupleHashEntry_internal(hashtable, slot, isnew, hash);
+	Assert(entry == NULL || entry->hash == hash);
 
 	MemoryContextSwitchTo(oldContext);
 
@@ -480,7 +489,7 @@ TupleHashTableHash_internal(struct tuplehash_hash *tb,
  * NB: This function may or may not change the memory context. Caller is
  * expected to change it back.
  */
-static TupleHashEntry
+static inline TupleHashEntry
 LookupTupleHashEntry_internal(TupleHashTable hashtable, TupleTableSlot *slot,
 							  bool *isnew, uint32 hash)
 {

src/backend/executor/nodeAgg.c

@@ -391,7 +391,9 @@ static void finalize_partialaggregate(AggState *aggstate,
 									  AggStatePerAgg peragg,
 									  AggStatePerGroup pergroupstate,
 									  Datum *resultVal, bool *resultIsNull);
-static void prepare_hash_slot(AggState *aggstate);
+static inline void prepare_hash_slot(AggStatePerHash perhash,
+									 TupleTableSlot *inputslot,
+									 TupleTableSlot *hashslot);
 static void prepare_projection_slot(AggState *aggstate,
 									TupleTableSlot *slot,
 									int currentSet);
@@ -413,8 +415,9 @@ static int	hash_choose_num_partitions(uint64 input_groups,
 									   double hashentrysize,
 									   int used_bits,
 									   int *log2_npartittions);
-static AggStatePerGroup lookup_hash_entry(AggState *aggstate, uint32 hash,
-										  bool *in_hash_table);
+static void initialize_hash_entry(AggState *aggstate,
+								  TupleHashTable hashtable,
+								  TupleHashEntry entry);
 static void lookup_hash_entries(AggState *aggstate);
 static TupleTableSlot *agg_retrieve_direct(AggState *aggstate);
 static void agg_fill_hash_table(AggState *aggstate);
@@ -1207,12 +1210,11 @@ finalize_partialaggregate(AggState *aggstate,
  * Extract the attributes that make up the grouping key into the
  * hashslot. This is necessary to compute the hash or perform a lookup.
  */
-static void
-prepare_hash_slot(AggState *aggstate)
+static inline void
+prepare_hash_slot(AggStatePerHash perhash,
+				  TupleTableSlot *inputslot,
+				  TupleTableSlot *hashslot)
 {
-	TupleTableSlot *inputslot = aggstate->tmpcontext->ecxt_outertuple;
-	AggStatePerHash perhash = &aggstate->perhash[aggstate->current_set];
-	TupleTableSlot *hashslot = perhash->hashslot;
 	int			i;
 
 	/* transfer just the needed columns into hashslot */
@@ -2013,75 +2015,39 @@ hash_choose_num_partitions(uint64 input_groups, double hashentrysize,
 }
 
 /*
- * Find or create a hashtable entry for the tuple group containing the current
- * tuple (already set in tmpcontext's outertuple slot), in the current grouping
- * set (which the caller must have selected - note that initialize_aggregate
- * depends on this).
- *
- * When called, CurrentMemoryContext should be the per-query context. The
- * already-calculated hash value for the tuple must be specified.
- *
- * If in "spill mode", then only find existing hashtable entries; don't create
- * new ones. If a tuple's group is not already present in the hash table for
- * the current grouping set, assign *in_hash_table=false and the caller will
- * spill it to disk.
+ * Initialize a freshly-created TupleHashEntry.
  */
-static AggStatePerGroup
-lookup_hash_entry(AggState *aggstate, uint32 hash, bool *in_hash_table)
+static void
+initialize_hash_entry(AggState *aggstate, TupleHashTable hashtable,
+					  TupleHashEntry entry)
 {
-	AggStatePerHash perhash = &aggstate->perhash[aggstate->current_set];
-	TupleTableSlot *hashslot = perhash->hashslot;
-	TupleHashEntryData *entry;
-	bool		isnew = false;
-	bool	   *p_isnew;
-
-	/* if hash table already spilled, don't create new entries */
-	p_isnew = aggstate->hash_spill_mode ? NULL : &isnew;
-
-	/* find or create the hashtable entry using the filtered tuple */
-	entry = LookupTupleHashEntryHash(perhash->hashtable, hashslot, p_isnew,
-									 hash);
-
-	if (entry == NULL)
-	{
-		*in_hash_table = false;
-		return NULL;
-	}
-	else
-		*in_hash_table = true;
-
-	if (isnew)
-	{
-		AggStatePerGroup pergroup;
-		int			transno;
+	AggStatePerGroup pergroup;
+	int			transno;
 
-		aggstate->hash_ngroups_current++;
-		hash_agg_check_limits(aggstate);
+	aggstate->hash_ngroups_current++;
+	hash_agg_check_limits(aggstate);
 
-		/* no need to allocate or initialize per-group state */
-		if (aggstate->numtrans == 0)
-			return NULL;
+	/* no need to allocate or initialize per-group state */
+	if (aggstate->numtrans == 0)
+		return;
 
-		pergroup = (AggStatePerGroup)
-			MemoryContextAlloc(perhash->hashtable->tablecxt,
-							   sizeof(AggStatePerGroupData) * aggstate->numtrans);
+	pergroup = (AggStatePerGroup)
+		MemoryContextAlloc(hashtable->tablecxt,
+						   sizeof(AggStatePerGroupData) * aggstate->numtrans);
 
-		entry->additional = pergroup;
+	entry->additional = pergroup;
 
-		/*
-		 * Initialize aggregates for new tuple group, lookup_hash_entries()
-		 * already has selected the relevant grouping set.
-		 */
-		for (transno = 0; transno < aggstate->numtrans; transno++)
-		{
-			AggStatePerTrans pertrans = &aggstate->pertrans[transno];
-			AggStatePerGroup pergroupstate = &pergroup[transno];
+	/*
+	 * Initialize aggregates for new tuple group, lookup_hash_entries()
+	 * already has selected the relevant grouping set.
+	 */
+	for (transno = 0; transno < aggstate->numtrans; transno++)
+	{
+		AggStatePerTrans pertrans = &aggstate->pertrans[transno];
+		AggStatePerGroup pergroupstate = &pergroup[transno];
 
-			initialize_aggregate(aggstate, pertrans, pergroupstate);
-		}
+		initialize_aggregate(aggstate, pertrans, pergroupstate);
 	}
-
-	return entry->additional;
 }
 
 /*
@@ -2106,21 +2072,37 @@ static void
 lookup_hash_entries(AggState *aggstate)
 {
 	AggStatePerGroup *pergroup = aggstate->hash_pergroup;
+	TupleTableSlot *outerslot = aggstate->tmpcontext->ecxt_outertuple;
 	int			setno;
 
 	for (setno = 0; setno < aggstate->num_hashes; setno++)
 	{
 		AggStatePerHash perhash = &aggstate->perhash[setno];
+		TupleHashTable hashtable = perhash->hashtable;
+		TupleTableSlot *hashslot = perhash->hashslot;
+		TupleHashEntry entry;
 		uint32		hash;
-		bool		in_hash_table;
+		bool		isnew = false;
+		bool	   *p_isnew;
+
+		/* if hash table already spilled, don't create new entries */
+		p_isnew = aggstate->hash_spill_mode ? NULL : &isnew;
 
 		select_current_set(aggstate, setno, true);
-		prepare_hash_slot(aggstate);
-		hash = TupleHashTableHash(perhash->hashtable, perhash->hashslot);
-		pergroup[setno] = lookup_hash_entry(aggstate, hash, &in_hash_table);
+		prepare_hash_slot(perhash,
+						  outerslot,
+						  hashslot);
+
+		entry = LookupTupleHashEntry(hashtable, hashslot,
+									 p_isnew, &hash);
 
-		/* check to see if we need to spill the tuple for this grouping set */
-		if (!in_hash_table)
+		if (entry != NULL)
+		{
+			if (isnew)
+				initialize_hash_entry(aggstate, hashtable, entry);
+			pergroup[setno] = entry->additional;
+		}
+		else
 		{
 			HashAggSpill *spill = &aggstate->hash_spills[setno];
 			TupleTableSlot *slot = aggstate->tmpcontext->ecxt_outertuple;
@@ -2131,6 +2113,7 @@ lookup_hash_entries(AggState *aggstate)
 								   aggstate->hashentrysize);
 
 			hashagg_spill_tuple(aggstate, spill, slot, hash);
+			pergroup[setno] = NULL;
 		}
 	}
 }
@@ -2588,6 +2571,7 @@ static bool
 agg_refill_hash_table(AggState *aggstate)
 {
 	HashAggBatch *batch;
+	AggStatePerHash perhash;
 	HashAggSpill spill;
 	HashTapeInfo *tapeinfo = aggstate->hash_tapeinfo;
 	uint64		ngroups_estimate;
@@ -2639,6 +2623,8 @@ agg_refill_hash_table(AggState *aggstate)
 
 	select_current_set(aggstate, batch->setno, true);
 
+	perhash = &aggstate->perhash[aggstate->current_set];
+
 	/*
 	 * Spilled tuples are always read back as MinimalTuples, which may be
 	 * different from the outer plan, so recompile the aggregate expressions.
@@ -2652,10 +2638,13 @@ agg_refill_hash_table(AggState *aggstate)
 							 HASHAGG_READ_BUFFER_SIZE);
 	for (;;)
 	{
-		TupleTableSlot *slot = aggstate->hash_spill_rslot;
+		TupleTableSlot *spillslot = aggstate->hash_spill_rslot;
+		TupleTableSlot *hashslot = perhash->hashslot;
+		TupleHashEntry entry;
 		MinimalTuple tuple;
 		uint32		hash;
-		bool		in_hash_table;
+		bool		isnew = false;
+		bool	   *p_isnew = aggstate->hash_spill_mode ? NULL : &isnew;
 
 		CHECK_FOR_INTERRUPTS();
 
@@ -2663,16 +2652,20 @@ agg_refill_hash_table(AggState *aggstate)
 		if (tuple == NULL)
 			break;
 
-		ExecStoreMinimalTuple(tuple, slot, true);
-		aggstate->tmpcontext->ecxt_outertuple = slot;
+		ExecStoreMinimalTuple(tuple, spillslot, true);
+		aggstate->tmpcontext->ecxt_outertuple = spillslot;
 
-		prepare_hash_slot(aggstate);
-		aggstate->hash_pergroup[batch->setno] =
-			lookup_hash_entry(aggstate, hash, &in_hash_table);
+		prepare_hash_slot(perhash,
+						  aggstate->tmpcontext->ecxt_outertuple,
+						  hashslot);
+		entry = LookupTupleHashEntryHash(
+										 perhash->hashtable, hashslot, p_isnew, hash);
 
-		if (in_hash_table)
+		if (entry != NULL)
 		{
-			/* Advance the aggregates (or combine functions) */
+			if (isnew)
+				initialize_hash_entry(aggstate, perhash->hashtable, entry);
+			aggstate->hash_pergroup[batch->setno] = entry->additional;
 			advance_aggregates(aggstate);
 		}
 		else
@@ -2688,7 +2681,9 @@ agg_refill_hash_table(AggState *aggstate)
 								   ngroups_estimate, aggstate->hashentrysize);
 			}
 			/* no memory for a new group, spill */
-			hashagg_spill_tuple(aggstate, &spill, slot, hash);
+			hashagg_spill_tuple(aggstate, &spill, spillslot, hash);
+
+			aggstate->hash_pergroup[batch->setno] = NULL;
 		}
 
 		/*

src/backend/executor/nodeRecursiveunion.c

@@ -94,7 +94,7 @@ ExecRecursiveUnion(PlanState *pstate)
 			if (plan->numCols > 0)
 			{
 				/* Find or build hashtable entry for this tuple's group */
-				LookupTupleHashEntry(node->hashtable, slot, &isnew);
+				LookupTupleHashEntry(node->hashtable, slot, &isnew, NULL);
 				/* Must reset temp context after each hashtable lookup */
 				MemoryContextReset(node->tempContext);
 				/* Ignore tuple if already seen */
@@ -141,7 +141,7 @@ ExecRecursiveUnion(PlanState *pstate)
 		if (plan->numCols > 0)
 		{
 			/* Find or build hashtable entry for this tuple's group */
-			LookupTupleHashEntry(node->hashtable, slot, &isnew);
+			LookupTupleHashEntry(node->hashtable, slot, &isnew, NULL);
 			/* Must reset temp context after each hashtable lookup */
 			MemoryContextReset(node->tempContext);
 			/* Ignore tuple if already seen */

src/backend/executor/nodeSetOp.c

@@ -381,7 +381,7 @@ setop_fill_hash_table(SetOpState *setopstate)
 
 			/* Find or build hashtable entry for this tuple's group */
 			entry = LookupTupleHashEntry(setopstate->hashtable, outerslot,
-										 &isnew);
+										 &isnew, NULL);
 
 			/* If new tuple group, initialize counts */
 			if (isnew)
@@ -402,7 +402,7 @@ setop_fill_hash_table(SetOpState *setopstate)
 
 			/* For tuples not seen previously, do not make hashtable entry */
 			entry = LookupTupleHashEntry(setopstate->hashtable, outerslot,
-										 NULL);
+										 NULL, NULL);
 
 			/* Advance the counts if entry is already present */
 			if (entry)

src/backend/executor/nodeSubplan.c

@@ -595,12 +595,12 @@ buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
 		 */
 		if (slotNoNulls(slot))
 		{
-			(void) LookupTupleHashEntry(node->hashtable, slot, &isnew);
+			(void) LookupTupleHashEntry(node->hashtable, slot, &isnew, NULL);
 			node->havehashrows = true;
 		}
 		else if (node->hashnulls)
 		{
-			(void) LookupTupleHashEntry(node->hashnulls, slot, &isnew);
+			(void) LookupTupleHashEntry(node->hashnulls, slot, &isnew, NULL);
 			node->havenullrows = true;
 		}
 

src/include/executor/executor.h

@@ -139,7 +139,7 @@ extern TupleHashTable BuildTupleHashTableExt(PlanState *parent,
 											 MemoryContext tempcxt, bool use_variable_hash_iv);
 extern TupleHashEntry LookupTupleHashEntry(TupleHashTable hashtable,
 										   TupleTableSlot *slot,
-										   bool *isnew);
+										   bool *isnew, uint32 *hash);
 extern uint32 TupleHashTableHash(TupleHashTable hashtable,
 								 TupleTableSlot *slot);
 extern TupleHashEntry LookupTupleHashEntryHash(TupleHashTable hashtable,