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From: Daniil Davydov <[email protected]>
To: [email protected]
Subject: [BUG] temp_table_max_size parameter may entail an error within ReadBuffer function
Date: Fri, 6 Dec 2024 16:54:30 +0700
Message-ID: <CAJDiXgiFqaoqvFGLeyuda28EfFOV+yD3aTk2ST7kvzR0bASjZw@mail.gmail.com> (raw)

Hi,
I noticed that this sequence of actions (for temporary table) leads to
an error, if
temp_table_max_size parameter is set :
***
LockRelationForExtension(relation, ExclusiveLock);
buf = ReadBuffer(relation, P_NEW);
***

Error occurs during total temporary table size calculation
(find_total_temp_relation_size function,
that can be called only if temp_table_max_size parameter > 0) : we are
trying to open all table's
indexes and append their size to the total size of the temporary
table. But inside relation_open function
(called for index) we meet this assert (and, of course, fail on it):

***
/*
 * We don't acquire any other heavyweight lock while holding the relation
 * extension lock.  We do allow to acquire the same relation extension
 * lock more than once but that case won't reach here.
 */
Assert(!IsRelationExtensionLockHeld);
***

I suppose that the simplest way out of the situation would be to skip
locking temporary tables for
extension

--
Best regards,
Daniil Davydov


Attachments:

  [text/x-patch] 0001-Fix-bug-with-locking-temp-relation-for-extension.patch (787B, ../CAJDiXgiFqaoqvFGLeyuda28EfFOV+yD3aTk2ST7kvzR0bASjZw@mail.gmail.com/2-0001-Fix-bug-with-locking-temp-relation-for-extension.patch)
  download | inline diff:
From da84d916e568be0d2414303f4a1e1d01b0bc6abd Mon Sep 17 00:00:00 2001
From: Daniil Davidov <[email protected]>
Date: Fri, 6 Dec 2024 16:41:53 +0700
Subject: [PATCH] Fix bug with locking temp relation for extension

---
 src/backend/storage/lmgr/lmgr.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c
index 094522acb4..0a91109d03 100644
--- a/src/backend/storage/lmgr/lmgr.c
+++ b/src/backend/storage/lmgr/lmgr.c
@@ -421,6 +421,9 @@ LockRelationForExtension(Relation relation, LOCKMODE lockmode)
 {
 	LOCKTAG		tag;
 
+	if (relation->rd_islocaltemp)
+		return;
+
 	SET_LOCKTAG_RELATION_EXTEND(tag,
 								relation->rd_lockInfo.lockRelId.dbId,
 								relation->rd_lockInfo.lockRelId.relId);
-- 
2.43.0

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