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Block replication slot advance for these not yet reserving WAL

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Such replication slots are physical slots freshly created without WAL
being reserved, which is the default behavior, which have not been used
yet as WAL consumption resources to retain WAL.  This prevents advancing
a slot to a position older than any WAL available, which could falsify
calculations for WAL segment recycling.

This also cleans up a bit the code, as ReplicationSlotRelease() would be
called on ERROR, and improves error messages.

Reported-by: Kyotaro Horiguchi
Author: Michael Paquier
Reviewed-by: Andres Freund, Álvaro Herrera, Kyotaro Horiguchi
Discussion: https://postgr.es/m/20180626071305.GH31353@paquier.xyz
This commit is contained in:
Michael Paquier 2018-07-11 08:56:24 +09:00
parent b6e3a3a492
commit 56a7147213
4 changed files with 33 additions and 6 deletions
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17
contrib/test_decoding/expected/slot.out
View File

@ -131,3 +131,20 @@ SELECT pg_drop_replication_slot('regression_slot1');
ERROR: replication slot "regression_slot1" does not exist
SELECT pg_drop_replication_slot('regression_slot2');
ERROR: replication slot "regression_slot2" does not exist
-- slot advance with physical slot, error with non-reserved slot
SELECT slot_name FROM pg_create_physical_replication_slot('regression_slot3');
slot_name
------------------
regression_slot3
(1 row)
SELECT pg_replication_slot_advance('regression_slot3', '0/0'); -- invalid LSN
ERROR: invalid target wal lsn
SELECT pg_replication_slot_advance('regression_slot3', '0/1'); -- error
ERROR: cannot advance replication slot that has not previously reserved WAL
SELECT pg_drop_replication_slot('regression_slot3');
pg_drop_replication_slot
--------------------------
(1 row)

6
contrib/test_decoding/sql/slot.sql
View File

@ -68,3 +68,9 @@ SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot1', 'test_
-- both should error as they should be dropped on error
SELECT pg_drop_replication_slot('regression_slot1');
SELECT pg_drop_replication_slot('regression_slot2');
-- slot advance with physical slot, error with non-reserved slot
SELECT slot_name FROM pg_create_physical_replication_slot('regression_slot3');
SELECT pg_replication_slot_advance('regression_slot3', '0/0'); -- invalid LSN
SELECT pg_replication_slot_advance('regression_slot3', '0/1'); -- error
SELECT pg_drop_replication_slot('regression_slot3');

3
doc/src/sgml/catalogs.sgml
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@ -9867,7 +9867,8 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
<entry></entry>
<entry>The address (<literal>LSN</literal>) of oldest WAL which still
might be required by the consumer of this slot and thus won't be
automatically removed during checkpoints.
automatically removed during checkpoints. <literal>NULL</literal>
if the <literal>LSN</literal> of this slot has never been reserved.
</entry>
</row>

13
src/backend/replication/slotfuncs.c
View File

@ -483,6 +483,12 @@ pg_replication_slot_advance(PG_FUNCTION_ARGS)
/* Acquire the slot so we "own" it */
ReplicationSlotAcquire(NameStr(*slotname), true);
/* A slot whose restart_lsn has never been reserved cannot be advanced */
if (XLogRecPtrIsInvalid(MyReplicationSlot->data.restart_lsn))
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("cannot advance replication slot that has not previously reserved WAL")));
/*
* Check if the slot is not moving backwards. Physical slots rely simply
* on restart_lsn as a minimum point, while logical slots have confirmed
@ -495,14 +501,11 @@ pg_replication_slot_advance(PG_FUNCTION_ARGS)
minlsn = MyReplicationSlot->data.restart_lsn;
if (moveto < minlsn)
{
ReplicationSlotRelease();
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot move slot to %X/%X, minimum is %X/%X",
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("cannot advance replication slot to %X/%X, minimum is %X/%X",
(uint32) (moveto >> 32), (uint32) moveto,
(uint32) (minlsn >> 32), (uint32) minlsn)));
}
/* Do the actual slot update, depending on the slot type */
if (OidIsValid(MyReplicationSlot->data.database))