From 72619f81916315658711cf35bcb2d3c993960bd4 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 27 Dec 2006 22:31:54 +0000
Subject: [PATCH] Modify local buffer management to request memory for local
buffers in blocks of increasing size, instead of one at a time. This reduces
the memory management overhead when num_temp_buffers is large: in the
previous coding we would actually waste 50% of the space used for temp
buffers, because aset.c would round the individual requests up to 16K.
Problem noted while studying a performance issue reported by Steven Flatt.
Back-patch as far as 8.1 --- older versions used few enough local buffers
that the issue isn't significant for them.
---
src/backend/storage/buffer/localbuf.c | 57 ++++++++++++++++++++++++---
1 file changed, 51 insertions(+), 6 deletions(-)
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 31d5c27e79..36dd50e71f 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.74 2006/03/31 23:32:06 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.75 2006/12/27 22:31:54 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -48,6 +48,7 @@ static HTAB *LocalBufHash = NULL;
static void InitLocalBuffers(void);
+static Block GetLocalBufferStorage(void);
/*
@@ -167,12 +168,8 @@ LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
*/
if (LocalBufHdrGetBlock(bufHdr) == NULL)
{
- char *data;
-
- data = (char *) MemoryContextAlloc(TopMemoryContext, BLCKSZ);
-
/* Set pointer for use by BufferGetBlock() macro */
- LocalBufHdrGetBlock(bufHdr) = (Block) data;
+ LocalBufHdrGetBlock(bufHdr) = GetLocalBufferStorage();
}
/*
@@ -334,6 +331,54 @@ InitLocalBuffers(void)
NLocBuffer = nbufs;
}
+/*
+ * GetLocalBufferStorage - allocate memory for a local buffer
+ *
+ * The idea of this function is to aggregate our requests for storage
+ * so that the memory manager doesn't see a whole lot of relatively small
+ * requests. Since we'll never give back a local buffer once it's created
+ * within a particular process, no point in burdening memmgr with separately
+ * managed chunks.
+ */
+static Block
+GetLocalBufferStorage(void)
+{
+ static char *cur_block = NULL;
+ static int next_buf_in_block = 0;
+ static int num_bufs_in_block = 0;
+ static int total_bufs_allocated = 0;
+
+ char *this_buf;
+
+ Assert(total_bufs_allocated < NLocBuffer);
+
+ if (next_buf_in_block >= num_bufs_in_block)
+ {
+ /* Need to make a new request to memmgr */
+ int num_bufs;
+
+ /* Start with a 16-buffer request; subsequent ones double each time */
+ num_bufs = Max(num_bufs_in_block * 2, 16);
+ /* But not more than what we need for all remaining local bufs */
+ num_bufs = Min(num_bufs, NLocBuffer - total_bufs_allocated);
+ /* And don't overflow MaxAllocSize, either */
+ num_bufs = Min(num_bufs, MaxAllocSize / BLCKSZ);
+
+ /* Allocate space from TopMemoryContext so it never goes away */
+ cur_block = (char *) MemoryContextAlloc(TopMemoryContext,
+ num_bufs * BLCKSZ);
+ next_buf_in_block = 0;
+ num_bufs_in_block = num_bufs;
+ }
+
+ /* Allocate next buffer in current memory block */
+ this_buf = cur_block + next_buf_in_block * BLCKSZ;
+ next_buf_in_block++;
+ total_bufs_allocated++;
+
+ return (Block) this_buf;
+}
+
/*
* AtEOXact_LocalBuffers - clean up at end of transaction.
*
--
2.50.0