From fc5eb3f69a32f1bc5109576f5725dbdc33cdc1ca Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 8 Nov 2006 19:24:38 +0000
Subject: [PATCH] Tweak accumArrayResult() to double the size of its working
 arrays when more space is needed, instead of incrementing by a fixed amount;
 the old method wastes lots of space and time when the ultimate size is large.
 Per gripe from Tatsuo.

---
 src/backend/utils/adt/arrayfuncs.c | 18 ++++++++----------
 src/include/utils/array.h          | 11 +++--------
 2 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index b510d42bb9..667335b5ab 100644
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/arrayfuncs.c,v 1.134 2006/10/06 17:13:59 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/arrayfuncs.c,v 1.135 2006/11/08 19:24:38 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -4337,10 +4337,9 @@ accumArrayResult(ArrayBuildState *astate,
 		oldcontext = MemoryContextSwitchTo(arr_context);
 		astate = (ArrayBuildState *) palloc(sizeof(ArrayBuildState));
 		astate->mcontext = arr_context;
-		astate->dvalues = (Datum *)
-			palloc(ARRAY_ELEMS_CHUNKSIZE * sizeof(Datum));
-		astate->dnulls = (bool *)
-			palloc(ARRAY_ELEMS_CHUNKSIZE * sizeof(bool));
+		astate->alen = 64;		/* arbitrary starting array size */
+		astate->dvalues = (Datum *) palloc(astate->alen * sizeof(Datum));
+		astate->dnulls = (bool *) palloc(astate->alen * sizeof(bool));
 		astate->nelems = 0;
 		astate->element_type = element_type;
 		get_typlenbyvalalign(element_type,
@@ -4353,14 +4352,13 @@ accumArrayResult(ArrayBuildState *astate,
 		oldcontext = MemoryContextSwitchTo(astate->mcontext);
 		Assert(astate->element_type == element_type);
 		/* enlarge dvalues[]/dnulls[] if needed */
-		if ((astate->nelems % ARRAY_ELEMS_CHUNKSIZE) == 0)
+		if (astate->nelems >= astate->alen)
 		{
+			astate->alen *= 2;
 			astate->dvalues = (Datum *)
-				repalloc(astate->dvalues,
-				   (astate->nelems + ARRAY_ELEMS_CHUNKSIZE) * sizeof(Datum));
+				repalloc(astate->dvalues, astate->alen * sizeof(Datum));
 			astate->dnulls = (bool *)
-				repalloc(astate->dnulls,
-					(astate->nelems + ARRAY_ELEMS_CHUNKSIZE) * sizeof(bool));
+				repalloc(astate->dnulls, astate->alen * sizeof(bool));
 		}
 	}
 
diff --git a/src/include/utils/array.h b/src/include/utils/array.h
index a273ee765e..791f6ebd99 100644
--- a/src/include/utils/array.h
+++ b/src/include/utils/array.h
@@ -49,7 +49,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/array.h,v 1.59 2006/09/10 20:14:20 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/utils/array.h,v 1.60 2006/11/08 19:24:38 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -78,13 +78,8 @@ typedef struct ArrayBuildState
 	MemoryContext mcontext;		/* where all the temp stuff is kept */
 	Datum	   *dvalues;		/* array of accumulated Datums */
 	bool	   *dnulls;			/* array of is-null flags for Datums */
-
-	/*
-	 * The allocated size of dvalues[] and dnulls[] is always a multiple of
-	 * ARRAY_ELEMS_CHUNKSIZE
-	 */
-#define ARRAY_ELEMS_CHUNKSIZE	64
-	int			nelems;			/* number of valid Datums in dvalues[] */
+	int			alen;			/* allocated length of above arrays */
+	int			nelems;			/* number of valid entries in above arrays */
 	Oid			element_type;	/* data type of the Datums */
 	int16		typlen;			/* needed info about datatype */
 	bool		typbyval;
-- 
2.11.0