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Fix assertion failure in snapshot building

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Clear any potential stale next_phase_at value from the snapshot
builder which otherwise may trip an assertion check ensuring
that there is no next_phase_at value.

This can be reproduced by running 80 concurrent sessions like
the below where $c is a loop counter (assumes there has been
1..$c databases created) :

  echo "
    CREATE TABLE replication_example(id SERIAL PRIMARY KEY,
                                     somedata int,
                                     text varchar(120));
    SELECT 'init' FROM
      pg_create_logical_replication_slot('regression_slot_$c',
                                         'test_decoding');
    SELECT data FROM
      pg_logical_slot_get_changes('regression_slot_$c', NULL,
                                  NULL, 'include-xids', '0',
                                  'skip-empty-xacts', '1');
  " | psql -d regress_$c >>psql.log &

Backpatch down to v16.

Bug: #17695
Author: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Alexander Lakhin <exclusion@gmail.com>
Reported-by: bowenshi <zxwsbg@qq.com>
Discussion: https://postgr.es/m/17695-6be9277c9295985f@postgresql.org
Backpatch-through: v16
This commit is contained in:
Daniel Gustafsson 2023-07-04 17:36:13 +02:00
parent d431644b43
commit eb27d3dc88
1 changed files with 5 additions and 1 deletions
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6
src/backend/replication/logical/snapbuild.c
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@ -1950,8 +1950,12 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
if (TransactionIdPrecedes(ondisk.builder.xmin, builder->initial_xmin_horizon))
goto snapshot_not_interesting;
/* consistent snapshots have no next phase */
/*
* Consistent snapshots have no next phase. Reset next_phase_at as it is
* possible that an old value may remain.
*/
Assert(ondisk.builder.next_phase_at == InvalidTransactionId);
builder->next_phase_at = InvalidTransactionId;
/* ok, we think the snapshot is sensible, copy over everything important */
builder->xmin = ondisk.builder.xmin;