From 8e6ef0c33af0d8b2c5f5bbecd4e46b6ca79d8e64 Mon Sep 17 00:00:00 2001
From: Matthias van de Meent <boekewurm+postgres@gmail.com>
Date: Tue, 6 Oct 2026 16:29:30 +0200
Subject: [PATCH v3 6/6] relcache: Reduce number of allocations into shape
 cache

Proxy contexts have low per-context overhead, but significant overhead
per allocation.  To reduce the per-context overhead, we allocate most
shape arrays in one go, so that we avoid increasing the total overhead.
---
 src/backend/utils/cache/relcache.c | 40 +++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 9 deletions(-)

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index d1a0cb3b011..a8850f04c27 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -1697,28 +1697,50 @@ IndexSupportInitialize(oidvector *indclass, AttrNumber nKeyAtts,
 		Oid		   *opcInType;
 		RegProcedure *support;
 		FmgrInfo   *supportinfo;
+		size_t		bulkallocSize = 0;
+		char	   *bulkalloc;
 		MemoryContext shapectx;
+		int			nprocs = maxSupportNumber * nKeyAtts;
+
+		/* supportinfo */
+		bulkallocSize += sizeof(FmgrInfo) * nprocs;
+		/* support */
+		bulkallocSize += sizeof(RegProcedure) * nprocs;
+		/* opcInType */
+		bulkallocSize += sizeof(Oid) * nKeyAtts;
+		/* opFamily */
+		bulkallocSize += sizeof(Oid) * nKeyAtts;
 
 		shapectx = ProxyContextCreate(RelShapeContext, "index shape");
 
+		bulkalloc = MemoryContextAllocZero(shapectx, bulkallocSize);
+
 		if (maxSupportNumber > 0)
 		{
-			int		nprocs = maxSupportNumber * nKeyAtts;
-			supportinfo = (FmgrInfo *)
-				MemoryContextAllocZero(shapectx, nprocs * sizeof(FmgrInfo));
-			support = (RegProcedure *)
-				MemoryContextAllocZero(shapectx, nprocs * sizeof(RegProcedure));
+			supportinfo = (FmgrInfo *) bulkalloc;
+			bulkalloc += nprocs * sizeof(FmgrInfo);
+			bulkallocSize -= nprocs * sizeof(FmgrInfo);
+
+			support = (RegProcedure *) bulkalloc;
+			bulkalloc += nprocs * sizeof(RegProcedure);
+			bulkallocSize -= nprocs * sizeof(RegProcedure);
 		}
 		else
 		{
+			Assert(nprocs == 0);
 			supportinfo = NULL;
 			support = NULL;
 		}
 
-		opFamily = (Oid *)
-			MemoryContextAllocZero(shapectx, nKeyAtts * sizeof(Oid));
-		opcInType = (Oid *)
-			MemoryContextAllocZero(shapectx, nKeyAtts * sizeof(Oid));
+		opFamily = (Oid *) bulkalloc;
+		bulkalloc += nKeyAtts * sizeof(Oid);
+		bulkallocSize -= nKeyAtts * sizeof(Oid);
+
+		opcInType = (Oid *) bulkalloc;
+		bulkalloc += nKeyAtts * sizeof(Oid);
+		bulkallocSize -= nKeyAtts * sizeof(Oid);
+
+		Assert(bulkallocSize == 0);
 
 		for (int attIndex = 0; attIndex < nKeyAtts; attIndex++)
 		{
-- 
2.54.0 (Apple Git-157)