Use more efficient hashtable for execGrouping.c to speed up hash aggregation.

The more efficient hashtable speeds up hash-aggregations with more than
a few hundred groups significantly. Improvements of over 120% have been
measured.

Due to the the different hash table queries that not fully
determined (e.g. GROUP BY without ORDER BY) may change their result
order.

The conversion is largely straight-forward, except that, due to the
static element types of simplehash.h type hashes, the additional data
some users store in elements (e.g. the per-group working data for hash
aggregaters) is now stored in TupleHashEntryData->additional.  The
meaning of BuildTupleHashTable's entrysize (renamed to additionalsize)
has been changed to only be about the additionally stored size.  That
size is only used for the initial sizing of the hash-table.

Reviewed-By: Tomas Vondra
Discussion: <20160727004333.r3e2k2y6fvk2ntup@alap3.anarazel.de>

Author: anarazel

src/backend/executor/execGrouping.c

@@ -23,12 +23,25 @@
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 
+static uint32 TupleHashTableHash(struct tuplehash_hash *tb, const MinimalTuple tuple);
+static int	TupleHashTableMatch(struct tuplehash_hash *tb, const MinimalTuple tuple1, const MinimalTuple tuple2);
 
-static TupleHashTable CurTupleHashTable = NULL;
-
-static uint32 TupleHashTableHash(const void *key, Size keysize);
-static int TupleHashTableMatch(const void *key1, const void *key2,
-					Size keysize);
+/*
+ * Define parameters for tuple hash table code generation. The interface is
+ * *also* declared in execnodes.h (to generate the types, which are externally
+ * visible).
+ */
+#define SH_PREFIX tuplehash
+#define SH_ELEMENT_TYPE TupleHashEntryData
+#define SH_KEY_TYPE MinimalTuple
+#define SH_KEY firstTuple
+#define SH_HASH_KEY(tb, key) TupleHashTableHash(tb, key)
+#define SH_EQUAL(tb, a, b) TupleHashTableMatch(tb, a, b) == 0
+#define SH_SCOPE extern
+#define SH_STORE_HASH
+#define SH_GET_HASH(tb, a) a->hash
+#define SH_DEFINE
+#include "lib/simplehash.h"
 
 
 /*****************************************************************************
@@ -260,7 +273,7 @@ execTuplesHashPrepare(int numCols,
  *	eqfunctions: equality comparison functions to use
  *	hashfunctions: datatype-specific hashing functions to use
  *	nbuckets: initial estimate of hashtable size
- *	entrysize: size of each entry (at least sizeof(TupleHashEntryData))
+ *	additionalsize: size of data stored in ->additional
  *	tablecxt: memory context in which to store table and table entries
  *	tempcxt: short-lived context for evaluation hash and comparison functions
  *
@@ -275,20 +288,19 @@ TupleHashTable
 BuildTupleHashTable(int numCols, AttrNumber *keyColIdx,
 					FmgrInfo *eqfunctions,
 					FmgrInfo *hashfunctions,
-					long nbuckets, Size entrysize,
+					long nbuckets, Size additionalsize,
 					MemoryContext tablecxt, MemoryContext tempcxt)
 {
 	TupleHashTable hashtable;
-	HASHCTL		hash_ctl;
+	Size		entrysize = sizeof(TupleHashEntryData) + additionalsize;
 
 	Assert(nbuckets > 0);
-	Assert(entrysize >= sizeof(TupleHashEntryData));
 
 	/* Limit initial table size request to not more than work_mem */
 	nbuckets = Min(nbuckets, (long) ((work_mem * 1024L) / entrysize));
 
-	hashtable = (TupleHashTable) MemoryContextAlloc(tablecxt,
-												 sizeof(TupleHashTableData));
+	hashtable = (TupleHashTable)
+		MemoryContextAlloc(tablecxt, sizeof(TupleHashTableData));
 
 	hashtable->numCols = numCols;
 	hashtable->keyColIdx = keyColIdx;
@@ -302,15 +314,8 @@ BuildTupleHashTable(int numCols, AttrNumber *keyColIdx,
 	hashtable->in_hash_funcs = NULL;
 	hashtable->cur_eq_funcs = NULL;
 
-	MemSet(&hash_ctl, 0, sizeof(hash_ctl));
-	hash_ctl.keysize = sizeof(TupleHashEntryData);
-	hash_ctl.entrysize = entrysize;
-	hash_ctl.hash = TupleHashTableHash;
-	hash_ctl.match = TupleHashTableMatch;
-	hash_ctl.hcxt = tablecxt;
-	hashtable->hashtab = hash_create("TupleHashTable", nbuckets,
-									 &hash_ctl,
-					HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);
+	hashtable->hashtab = tuplehash_create(tablecxt, nbuckets);
+	hashtable->hashtab->private = hashtable;
 
 	return hashtable;
 }
@@ -324,18 +329,17 @@ BuildTupleHashTable(int numCols, AttrNumber *keyColIdx,
  *
  * 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.  Any extra space in a new entry has been
- * zeroed.
+ * false if it existed already.  ->additional_data in the new entry has
+ * been zeroed.
  */
 TupleHashEntry
 LookupTupleHashEntry(TupleHashTable hashtable, TupleTableSlot *slot,
 					 bool *isnew)
 {
-	TupleHashEntry entry;
+	TupleHashEntryData *entry;
 	MemoryContext oldContext;
-	TupleHashTable saveCurHT;
-	TupleHashEntryData dummy;
 	bool		found;
+	MinimalTuple key;
 
 	/* If first time through, clone the input slot to make table slot */
 	if (hashtable->tableslot == NULL)
@@ -356,53 +360,37 @@ LookupTupleHashEntry(TupleHashTable hashtable, TupleTableSlot *slot,
 	/* Need to run the hash functions in short-lived context */
 	oldContext = MemoryContextSwitchTo(hashtable->tempcxt);
 
-	/*
-	 * Set up data needed by hash and match functions
-	 *
-	 * We save and restore CurTupleHashTable just in case someone manages to
-	 * invoke this code re-entrantly.
-	 */
+	/* set up data needed by hash and match functions */
 	hashtable->inputslot = slot;
 	hashtable->in_hash_funcs = hashtable->tab_hash_funcs;
 	hashtable->cur_eq_funcs = hashtable->tab_eq_funcs;
 
-	saveCurHT = CurTupleHashTable;
-	CurTupleHashTable = hashtable;
-
-	/* Search the hash table */
-	dummy.firstTuple = NULL;	/* flag to reference inputslot */
-	entry = (TupleHashEntry) hash_search(hashtable->hashtab,
-										 &dummy,
-										 isnew ? HASH_ENTER : HASH_FIND,
-										 &found);
+	key = NULL; /* flag to reference inputslot */
 
 	if (isnew)
 	{
+		entry = tuplehash_insert(hashtable->hashtab, key, &found);
+
 		if (found)
 		{
 			/* found pre-existing entry */
 			*isnew = false;
 		}
 		else
 		{
-			/*
-			 * created new entry
-			 *
-			 * Zero any caller-requested space in the entry.  (This zaps the
-			 * "key data" dynahash.c copied into the new entry, but we don't
-			 * care since we're about to overwrite it anyway.)
-			 */
-			MemSet(entry, 0, hashtable->entrysize);
-
-			/* Copy the first tuple into the table context */
+			/* created new entry */
+			*isnew = true;
+			/* zero caller data */
+			entry->additional = NULL;
 			MemoryContextSwitchTo(hashtable->tablecxt);
+			/* Copy the first tuple into the table context */
 			entry->firstTuple = ExecCopySlotMinimalTuple(slot);
-
-			*isnew = true;
 		}
 	}
-
-	CurTupleHashTable = saveCurHT;
+	else
+	{
+		entry = tuplehash_lookup(hashtable->hashtab, key);
+	}
 
 	MemoryContextSwitchTo(oldContext);
 
@@ -425,34 +413,19 @@ FindTupleHashEntry(TupleHashTable hashtable, TupleTableSlot *slot,
 {
 	TupleHashEntry entry;
 	MemoryContext oldContext;
-	TupleHashTable saveCurHT;
-	TupleHashEntryData dummy;
+	MinimalTuple key;
 
 	/* Need to run the hash functions in short-lived context */
 	oldContext = MemoryContextSwitchTo(hashtable->tempcxt);
 
-	/*
-	 * Set up data needed by hash and match functions
-	 *
-	 * We save and restore CurTupleHashTable just in case someone manages to
-	 * invoke this code re-entrantly.
-	 */
+	/* Set up data needed by hash and match functions */
 	hashtable->inputslot = slot;
 	hashtable->in_hash_funcs = hashfunctions;
 	hashtable->cur_eq_funcs = eqfunctions;
 
-	saveCurHT = CurTupleHashTable;
-	CurTupleHashTable = hashtable;
-
 	/* Search the hash table */
-	dummy.firstTuple = NULL;	/* flag to reference inputslot */
-	entry = (TupleHashEntry) hash_search(hashtable->hashtab,
-										 &dummy,
-										 HASH_FIND,
-										 NULL);
-
-	CurTupleHashTable = saveCurHT;
-
+	key = NULL;					/* flag to reference inputslot */
+	entry = tuplehash_lookup(hashtable->hashtab, key);
 	MemoryContextSwitchTo(oldContext);
 
 	return entry;
@@ -468,22 +441,18 @@ FindTupleHashEntry(TupleHashTable hashtable, TupleTableSlot *slot,
  * This convention avoids the need to materialize virtual input tuples unless
  * they actually need to get copied into the table.
  *
- * CurTupleHashTable must be set before calling this, since dynahash.c
- * doesn't provide any API that would let us get at the hashtable otherwise.
- *
  * Also, the caller must select an appropriate memory context for running
  * the hash functions. (dynahash.c doesn't change CurrentMemoryContext.)
  */
 static uint32
-TupleHashTableHash(const void *key, Size keysize)
+TupleHashTableHash(struct tuplehash_hash *tb, const MinimalTuple tuple)
 {
-	MinimalTuple tuple = ((const TupleHashEntryData *) key)->firstTuple;
-	TupleTableSlot *slot;
-	TupleHashTable hashtable = CurTupleHashTable;
+	TupleHashTable hashtable = (TupleHashTable) tb->private;
 	int			numCols = hashtable->numCols;
 	AttrNumber *keyColIdx = hashtable->keyColIdx;
-	FmgrInfo   *hashfunctions;
 	uint32		hashkey = 0;
+	TupleTableSlot *slot;
+	FmgrInfo   *hashfunctions;
 	int			i;
 
 	if (tuple == NULL)
@@ -494,8 +463,12 @@ TupleHashTableHash(const void *key, Size keysize)
 	}
 	else
 	{
-		/* Process a tuple already stored in the table */
-		/* (this case never actually occurs in current dynahash.c code) */
+		/*
+		 * Process a tuple already stored in the table.
+		 *
+		 * (this case never actually occurs due to the way simplehash.h is
+		 * used, as the hash-value is stored in the entries)
+		 */
 		slot = hashtable->tableslot;
 		ExecStoreMinimalTuple(tuple, slot, false);
 		hashfunctions = hashtable->tab_hash_funcs;
@@ -530,29 +503,21 @@ TupleHashTableHash(const void *key, Size keysize)
  *
  * As above, the passed pointers are pointers to TupleHashEntryData.
  *
- * CurTupleHashTable must be set before calling this, since dynahash.c
- * doesn't provide any API that would let us get at the hashtable otherwise.
- *
  * Also, the caller must select an appropriate memory context for running
  * the compare functions.  (dynahash.c doesn't change CurrentMemoryContext.)
  */
 static int
-TupleHashTableMatch(const void *key1, const void *key2, Size keysize)
+TupleHashTableMatch(struct tuplehash_hash *tb, const MinimalTuple tuple1, const MinimalTuple tuple2)
 {
-	MinimalTuple tuple1 = ((const TupleHashEntryData *) key1)->firstTuple;
-
-#ifdef USE_ASSERT_CHECKING
-	MinimalTuple tuple2 = ((const TupleHashEntryData *) key2)->firstTuple;
-#endif
 	TupleTableSlot *slot1;
 	TupleTableSlot *slot2;
-	TupleHashTable hashtable = CurTupleHashTable;
+	TupleHashTable hashtable = (TupleHashTable) tb->private;
 
 	/*
-	 * We assume that dynahash.c will only ever call us with the first
+	 * We assume that simplehash.h will only ever call us with the first
 	 * argument being an actual table entry, and the second argument being
 	 * LookupTupleHashEntry's dummy TupleHashEntryData.  The other direction
-	 * could be supported too, but is not currently used by dynahash.c.
+	 * could be supported too, but is not currently required.
 	 */
 	Assert(tuple1 != NULL);
 	slot1 = hashtable->tableslot;