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Enable logical slots to follow timeline switches

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When decoding from a logical slot, it's necessary for xlog reading to be
able to read xlog from historical (i.e. not current) timelines;
otherwise, decoding fails after failover, because the archives are in
the historical timeline.  This is required to make "failover logical
slots" possible; it currently has no other use, although theoretically
it could be used by an extension that creates a slot on a standby and
continues to replay from the slot when the standby is promoted.

This commit includes a module in src/test/modules with functions to
manipulate the slots (which is not otherwise possible in SQL code) in
order to enable testing, and a new test in src/test/recovery to ensure
that the behavior is as expected.

Author: Craig Ringer
Reviewed-By: Oleksii Kliukin, Andres Freund, Petr Jelínek
This commit is contained in:
Alvaro Herrera
2016-03-30 20:07:05 -03:00
parent 3b02ea4f07
commit 24c5f1a103
16 changed files with 789 additions and 30 deletions
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17
src/backend/replication/logical/logicalfuncs.c
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@@ -231,12 +231,6 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
rsinfo->setResult = p->tupstore;
rsinfo->setDesc = p->tupdesc;
/* compute the current end-of-wal */
if (!RecoveryInProgress())
end_of_wal = GetFlushRecPtr();
else
end_of_wal = GetXLogReplayRecPtr(NULL);
ReplicationSlotAcquire(NameStr(*name));
PG_TRY();
@@ -273,7 +267,8 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
* slot's confirmed_flush. This means we might read xlog we don't
* actually decode rows from, but the snapshot builder might need it
* to get to a consistent point. The point we start returning data to
* *users* at is the candidate restart lsn from the decoding context.
* *users* at is the confirmed_flush lsn set up in the decoding
* context.
*/
startptr = MyReplicationSlot->data.restart_lsn;
@@ -282,8 +277,14 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
/* invalidate non-timetravel entries */
InvalidateSystemCaches();
if (!RecoveryInProgress())
end_of_wal = GetFlushRecPtr();
else
end_of_wal = GetXLogReplayRecPtr(NULL);
/* Decode until we run out of records */
while ((startptr != InvalidXLogRecPtr && startptr < end_of_wal) ||
(ctx->reader->EndRecPtr && ctx->reader->EndRecPtr < end_of_wal))
(ctx->reader->EndRecPtr != InvalidXLogRecPtr && ctx->reader->EndRecPtr < end_of_wal))
{
XLogRecord *record;
char *errm = NULL;