Hi,
For now we fully scan local buffers for each fork of the temporary
relation that we want to truncate (in order to drop its buffers). It
happens in the function "DropRelationBuffers".
There used to be the same problem for regular tables (i.e. shared
buffers) and it was fixed in commit [1] and now shared buffers are
scanned only one time for those three relation forks.
I suggest making the same fix for temporary relations. See attached patch.
[1] 6d05086c0a79e50d8e91ed953626ec7280cd2481
BTW, I see that we call "DropRelationBuffers" separately for relation,
toast table and indexes. What if we collect all this information in
advance and iterate over the local/shared buffers only once?
I understand that it will look kinda ugly, but it will increase
performance for sure.
--
Best regards,
Daniil Davydov
From 7b3c3e816b502a94d1ccc6889d86e07d2e1555fd Mon Sep 17 00:00:00 2001
From: Daniil Davidov <d.davy...@postgrespro.ru>
Date: Fri, 30 May 2025 17:50:47 +0700
Subject: [PATCH v1] Speedup temp table truncation
---
src/backend/storage/buffer/bufmgr.c | 8 +++-----
src/backend/storage/buffer/localbuf.c | 20 +++++++++++++-------
src/include/storage/buf_internals.h | 4 ++--
3 files changed, 18 insertions(+), 14 deletions(-)
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index f93131a645e..bd4c549eb14 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -4550,11 +4550,9 @@ DropRelationBuffers(SMgrRelation smgr_reln, ForkNumber *forkNum,
if (RelFileLocatorBackendIsTemp(rlocator))
{
if (rlocator.backend == MyProcNumber)
- {
- for (j = 0; j < nforks; j++)
- DropRelationLocalBuffers(rlocator.locator, forkNum[j],
- firstDelBlock[j]);
- }
+ DropRelationLocalBuffers(rlocator.locator, forkNum, nforks,
+ firstDelBlock);
+
return;
}
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 63101d56a07..7f51288546f 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -660,24 +660,30 @@ InvalidateLocalBuffer(BufferDesc *bufHdr, bool check_unreferenced)
* See DropRelationBuffers in bufmgr.c for more notes.
*/
void
-DropRelationLocalBuffers(RelFileLocator rlocator, ForkNumber forkNum,
- BlockNumber firstDelBlock)
+DropRelationLocalBuffers(RelFileLocator rlocator, ForkNumber *forkNum,
+ int nforks, BlockNumber *firstDelBlock)
{
int i;
+ int j;
for (i = 0; i < NLocBuffer; i++)
{
BufferDesc *bufHdr = GetLocalBufferDescriptor(i);
uint32 buf_state;
+ if (!BufTagMatchesRelFileLocator(&bufHdr->tag, &rlocator))
+ continue;
+
buf_state = pg_atomic_read_u32(&bufHdr->state);
- if ((buf_state & BM_TAG_VALID) &&
- BufTagMatchesRelFileLocator(&bufHdr->tag, &rlocator) &&
- BufTagGetForkNum(&bufHdr->tag) == forkNum &&
- bufHdr->tag.blockNum >= firstDelBlock)
+ for (j = 0; j < nforks; j++)
{
- InvalidateLocalBuffer(bufHdr, true);
+ if ((buf_state & BM_TAG_VALID) &&
+ BufTagGetForkNum(&bufHdr->tag) == forkNum[j] &&
+ bufHdr->tag.blockNum >= firstDelBlock[j])
+ {
+ InvalidateLocalBuffer(bufHdr, true);
+ }
}
}
}
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 0dec7d93b3b..52a71b138f7 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -486,8 +486,8 @@ extern bool StartLocalBufferIO(BufferDesc *bufHdr, bool forInput, bool nowait);
extern void FlushLocalBuffer(BufferDesc *bufHdr, SMgrRelation reln);
extern void InvalidateLocalBuffer(BufferDesc *bufHdr, bool check_unreferenced);
extern void DropRelationLocalBuffers(RelFileLocator rlocator,
- ForkNumber forkNum,
- BlockNumber firstDelBlock);
+ ForkNumber *forkNum, int nforks,
+ BlockNumber *firstDelBlock);
extern void DropRelationAllLocalBuffers(RelFileLocator rlocator);
extern void AtEOXact_LocalBuffers(bool isCommit);
--
2.43.0
