1 files changed, 55 insertions, 2 deletions

diff --git a/src/backend/executor/execGrouping.c b/src/backend/executor/execGrouping.c
index 33b124fbb0a..40f1776a7be 100644
--- a/src/backend/executor/execGrouping.c
+++ b/src/backend/executor/execGrouping.c
@@ -20,6 +20,13 @@
 #include "miscadmin.h"
 #include "utils/lsyscache.h"
 
+typedef struct TupleHashEntryData
+{
+	MinimalTuple firstTuple;	/* copy of first tuple in this group */
+	uint32		status;			/* hash status */
+	uint32		hash;			/* hash value (cached) */
+} TupleHashEntryData;
+
 static int	TupleHashTableMatch(struct tuplehash_hash *tb, const MinimalTuple tuple1, const MinimalTuple tuple2);
 static inline uint32 TupleHashTableHash_internal(struct tuplehash_hash *tb,
 												 const MinimalTuple tuple);
@@ -196,6 +203,7 @@ BuildTupleHashTable(PlanState *parent,
 	hashtable->tab_collations = collations;
 	hashtable->tablecxt = tablecxt;
 	hashtable->tempcxt = tempcxt;
+	hashtable->additionalsize = additionalsize;
 	hashtable->tableslot = NULL;	/* will be made on first lookup */
 	hashtable->inputslot = NULL;
 	hashtable->in_hash_expr = NULL;
@@ -274,6 +282,15 @@ ResetTupleHashTable(TupleHashTable hashtable)
 }
 
 /*
+ * Return size of the hash bucket. Useful for estimating memory usage.
+ */
+size_t
+TupleHashEntrySize(void)
+{
+	return sizeof(TupleHashEntryData);
+}
+
+/*
  * Find or create a hashtable entry for the tuple group containing the
  * given tuple.  The tuple must be the same type as the hashtable entries.
  *
@@ -339,6 +356,24 @@ TupleHashTableHash(TupleHashTable hashtable, TupleTableSlot *slot)
 	return hash;
 }
 
+MinimalTuple
+TupleHashEntryGetTuple(TupleHashEntry entry)
+{
+	return entry->firstTuple;
+}
+
+/*
+ * Get a pointer into the additional space allocated for this entry. The
+ * amount of space available is the additionalsize specified to
+ * BuildTupleHashTable(). If additionalsize was specified as zero, no
+ * additional space is available and this function should not be called.
+ */
+void *
+TupleHashEntryGetAdditional(TupleHashEntry entry)
+{
+	return (char *) entry->firstTuple + MAXALIGN(entry->firstTuple->t_len);
+}
+
 /*
  * A variant of LookupTupleHashEntry for callers that have already computed
  * the hash value.
@@ -477,13 +512,31 @@ LookupTupleHashEntry_internal(TupleHashTable hashtable, TupleTableSlot *slot,
 		}
 		else
 		{
+			MinimalTuple firstTuple;
+			size_t totalsize; /* including alignment and additionalsize */
+
 			/* 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);
+			firstTuple = ExecCopySlotMinimalTuple(slot);
+
+			/*
+			 * Allocate additional space right after the MinimalTuple of size
+			 * additionalsize. The caller can get a pointer to this data with
+			 * TupleHashEntryGetAdditional(), and store arbitrary data there.
+			 *
+			 * This avoids the need to store an extra pointer or allocate an
+			 * additional chunk, which would waste memory.
+			 */
+			totalsize = MAXALIGN(firstTuple->t_len) + hashtable->additionalsize;
+			firstTuple = repalloc(firstTuple, totalsize);
+			memset((char *) firstTuple + firstTuple->t_len, 0,
+				   totalsize - firstTuple->t_len);
+
+			entry->firstTuple = firstTuple;
 		}
 	}
 	else