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Commit9069eb9

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Block replication slot advance for these not yet reserving WAL
Such replication slots are physical slots freshly created without WALbeing reserved, which is the default behavior, which have not been usedyet as WAL consumption resources to retain WAL. This prevents advancinga slot to a position older than any WAL available, which could falsifycalculations for WAL segment recycling.This also cleans up a bit the code, as ReplicationSlotRelease() would becalled on ERROR, and improves error messages.Reported-by: Kyotaro HoriguchiAuthor: Michael PaquierReviewed-by: Andres Freund, Álvaro Herrera, Kyotaro HoriguchiDiscussion:https://postgr.es/m/20180626071305.GH31353@paquier.xyz
1 parente7df94f commit9069eb9

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4 files changed

+33
-6
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4 files changed

+33
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lines changed

‎contrib/test_decoding/expected/slot.out

Lines changed: 17 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -131,3 +131,20 @@ SELECT pg_drop_replication_slot('regression_slot1');
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ERROR: replication slot "regression_slot1" does not exist
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SELECT pg_drop_replication_slot('regression_slot2');
133133
ERROR: replication slot "regression_slot2" does not exist
134+
-- slot advance with physical slot, error with non-reserved slot
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SELECT slot_name FROM pg_create_physical_replication_slot('regression_slot3');
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slot_name
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------------------
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regression_slot3
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(1 row)
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SELECT pg_replication_slot_advance('regression_slot3', '0/0'); -- invalid LSN
142+
ERROR: invalid target wal lsn
143+
SELECT pg_replication_slot_advance('regression_slot3', '0/1'); -- error
144+
ERROR: cannot advance replication slot that has not previously reserved WAL
145+
SELECT pg_drop_replication_slot('regression_slot3');
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pg_drop_replication_slot
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--------------------------
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(1 row)
150+

‎contrib/test_decoding/sql/slot.sql

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -68,3 +68,9 @@ SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot1', 'test_
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-- both should error as they should be dropped on error
6969
SELECT pg_drop_replication_slot('regression_slot1');
7070
SELECT pg_drop_replication_slot('regression_slot2');
71+
72+
-- slot advance with physical slot, error with non-reserved slot
73+
SELECT slot_nameFROM pg_create_physical_replication_slot('regression_slot3');
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SELECT pg_replication_slot_advance('regression_slot3','0/0');-- invalid LSN
75+
SELECT pg_replication_slot_advance('regression_slot3','0/1');-- error
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SELECT pg_drop_replication_slot('regression_slot3');

‎doc/src/sgml/catalogs.sgml

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -9867,7 +9867,8 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
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<entry></entry>
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<entry>The address (<literal>LSN</literal>) of oldest WAL which still
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might be required by the consumer of this slot and thus won't be
9870-
automatically removed during checkpoints.
9870+
automatically removed during checkpoints. <literal>NULL</literal>
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if the <literal>LSN</literal> of this slot has never been reserved.
98719872
</entry>
98729873
</row>
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‎src/backend/replication/slotfuncs.c

Lines changed: 8 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -483,6 +483,12 @@ pg_replication_slot_advance(PG_FUNCTION_ARGS)
483483
/* Acquire the slot so we "own" it */
484484
ReplicationSlotAcquire(NameStr(*slotname), true);
485485

486+
/* A slot whose restart_lsn has never been reserved cannot be advanced */
487+
if (XLogRecPtrIsInvalid(MyReplicationSlot->data.restart_lsn))
488+
ereport(ERROR,
489+
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
490+
errmsg("cannot advance replication slot that has not previously reserved WAL")));
491+
486492
/*
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* Check if the slot is not moving backwards. Physical slots rely simply
488494
* on restart_lsn as a minimum point, while logical slots have confirmed
@@ -495,14 +501,11 @@ pg_replication_slot_advance(PG_FUNCTION_ARGS)
495501
minlsn=MyReplicationSlot->data.restart_lsn;
496502

497503
if (moveto<minlsn)
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{
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ReplicationSlotRelease();
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ereport(ERROR,
501-
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
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errmsg("cannotmove slot to %X/%X, minimum is %X/%X",
505+
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
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errmsg("cannotadvance replication slot to %X/%X, minimum is %X/%X",
503507
(uint32) (moveto >>32), (uint32)moveto,
504508
(uint32) (minlsn >>32), (uint32)minlsn)));
505-
}
506509

507510
/* Do the actual slot update, depending on the slot type */
508511
if (OidIsValid(MyReplicationSlot->data.database))

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