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Date: Tue, 4 Nov 2025 18:37:14 +0100
From: =?utf-8?Q?=C3=81lvaro?= Herrera <alvherre@kurilemu.de>
To: Michael Paquier <michael@paquier.xyz>
Cc: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: BRIN autosummarization lacking a snapshot
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On 2025-Nov-04, Álvaro Herrera wrote:

> Ah, the problem is that perform_work_item() pushes an active snapshot
> before calling the BRIN function, but because of the error, we
> terminate the transaction before returning, so when we try to Pop that
> snapshot, it doesn't exist anymore.  Other ways for this to happen would
> be an autovacuum worker trying to run an item for a dropped table (the
> "goto deleted2" case).

Of course, the answer is just to inquire ActiveSnapshotSet() beforehand.
I tested this by adding an elog(ERROR) in perform_work_item() -- without
this fix, I see a segfault, which disappears with it.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"Debido a que la velocidad de la luz es mucho mayor que la del sonido,
 algunas personas nos parecen brillantes un minuto antes
 de escuchar las pelotudeces que dicen." (Roberto Fontanarrosa)

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From 6558ceccdb96f37d3f1db8ad426ae02d1d29231c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81lvaro=20Herrera?= <alvherre@kurilemu.de>
Date: Tue, 4 Nov 2025 18:32:18 +0100
Subject: [PATCH] fix brin failure

---
 src/backend/postmaster/autovacuum.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 59ec45a4e96..ed19c74bb19 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2558,7 +2558,8 @@ deleted:
 
 		PushActiveSnapshot(GetTransactionSnapshot());
 		perform_work_item(workitem);
-		PopActiveSnapshot();
+		if (ActiveSnapshotSet())	/* transaction could have aborted */
+			PopActiveSnapshot();
 
 		/*
 		 * Check for config changes before acquiring lock for further jobs.
-- 
2.47.3


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