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Commit0fd38e1

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Don't skip SQL backends in logical decoding for visibility computation.
The logical decoding patchset introduced PROC_IN_LOGICAL_DECODING flagPGXACT flag, that allows such backends to be skipped when computingthe xmin horizon/snapshots. That's fine and sensible for walsendersstreaming out logical changes, but not at all fine for SQL backendsdoing logical decoding. If the latter set that flag any change theyhave performed outside of logical decoding will not be regarded asvisible - which e.g. can lead to that change being vacuumed away.Note that not setting the flag for SQL backends isn't particularlybothersome - the SQL backend doesn't do streaming, so it only runs fora limited amount of time.Per buildfarm member 'tick' and Alvaro.Backpatch to 9.4, where logical decoding was introduced.
1 parent75ef435 commit0fd38e1

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+19
-4
lines changed

4 files changed

+19
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‎contrib/test_decoding/expected/decoding_into_rel.out

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@@ -1,6 +1,8 @@
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-- test that we can insert the result of a get_changes call into a
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-- logged relation. That's really not a good idea in practical terms,
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-- but provides a nice test.
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-- predictability
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SET synchronous_commit = on;
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SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
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?column?
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----------

‎contrib/test_decoding/sql/decoding_into_rel.sql

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@@ -1,6 +1,10 @@
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-- test that we can insert the result of a get_changes call into a
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-- logged relation. That's really not a good idea in practical terms,
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-- but provides a nice test.
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-- predictability
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SET synchronous_commit=on;
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SELECT'init'FROM pg_create_logical_replication_slot('regression_slot','test_decoding');
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-- slot works

‎src/backend/replication/logical/logical.c

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@@ -146,10 +146,19 @@ StartupDecodingContext(List *output_plugin_options,
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* logical decoding backend which doesn't need to be checked individually
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* when computing the xmin horizon because the xmin is enforced via
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* replication slots.
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*
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* We can only do so if we're outside of a transaction (i.e. the case when
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* streaming changes via walsender), otherwise a already setup
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* snapshot/xid would end up being ignored. That's not a particularly
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* bothersome restriction since the SQL interface can't be used for
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* streaming anyway.
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*/
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LWLockAcquire(ProcArrayLock,LW_EXCLUSIVE);
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MyPgXact->vacuumFlags |=PROC_IN_LOGICAL_DECODING;
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LWLockRelease(ProcArrayLock);
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if (!IsTransactionOrTransactionBlock())
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{
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LWLockAcquire(ProcArrayLock,LW_EXCLUSIVE);
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MyPgXact->vacuumFlags |=PROC_IN_LOGICAL_DECODING;
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LWLockRelease(ProcArrayLock);
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}
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ctx->slot=slot;
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‎src/include/storage/proc.h

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@@ -43,7 +43,7 @@ struct XidCache
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#definePROC_IN_ANALYZE0x04/* currently running analyze */
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#definePROC_VACUUM_FOR_WRAPAROUND0x08/* set by autovac only */
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#definePROC_IN_LOGICAL_DECODING0x10/* currently doing logical
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* decoding */
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* decodingoutside xact*/
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/* flags reset at EOXact */
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#definePROC_VACUUM_STATE_MASK \

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