From: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
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To: | pgsql-committers(at)postgresql(dot)org |
Subject: | pgsql: Fix concurrent locking of tuple update chain |
Date: | 2017-07-26 21:27:26 |
Message-ID: | E1daTq2-0006UQ-Px@gemulon.postgresql.org |
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Lists: | pgsql-committers |
Fix concurrent locking of tuple update chain
If several sessions are concurrently locking a tuple update chain with
nonconflicting lock modes using an old snapshot, and they all succeed,
it may happen that some of them fail because of restarting the loop (due
to a concurrent Xmax change) and getting an error in the subsequent pass
while trying to obtain a tuple lock that they already have in some tuple
version.
This can only happen with very high concurrency (where a row is being
both updated and FK-checked by multiple transactions concurrently), but
it's been observed in the field and can have unpleasant consequences
such as an FK check failing to see a tuple that definitely exists:
ERROR: insert or update on table "child_table" violates foreign key constraint "fk_constraint_name"
DETAIL: Key (keyid)=(123456) is not present in table "parent_table".
(where the key is observably present in the table).
Discussion: https://postgr.es/m/20170714210011.r25mrff4nxjhmf3g@alvherre.pgsql
Branch
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master
Details
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https://git.postgresql.org/pg/commitdiff/459c64d3227f878c72ef0145a67e80e17728c556
Modified Files
--------------
src/backend/access/heap/heapam.c | 41 ++++++++++++++++++++++++++++++++++++----
1 file changed, 37 insertions(+), 4 deletions(-)
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