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Commite323d9d

Browse files
author
Amit Kapila
committed
Don't retreat slot's confirmed_flush LSN.
Prevent moving the confirmed_flush backwards, as this could lead to dataduplication issues caused by replicating already replicated changes.This can happen when a client acknowledges an LSN it doesn't have to doanything for, and thus didn't store persistently. After a restart, theclient can send the prior LSN that it stored persistently as anacknowledgement, but we need to ignore such an LSN to avoid retreatingconfirm_flush LSN.Diagnosed-by: Zhijie Hou <houzj.fnst@fujitsu.com>Author: shveta malik <shveta.malik@gmail.com>Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>Tested-by: Nisha Moond <nisha.moond412@gmail.com>Backpatch-through: 13Discussion:https://postgr.es/m/CAJpy0uDZ29P=BYB1JDWMCh-6wXaNqMwG1u1mB4=10Ly0x7HhwQ@mail.gmail.comDiscussion:https://postgr.es/m/OS0PR01MB57164AB5716AF2E477D53F6F9489A@OS0PR01MB5716.jpnprd01.prod.outlook.com
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‎src/backend/replication/logical/logical.c

Lines changed: 21 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1037,7 +1037,19 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
10371037

10381038
SpinLockAcquire(&MyReplicationSlot->mutex);
10391039

1040-
MyReplicationSlot->data.confirmed_flush=lsn;
1040+
/*
1041+
* Prevent moving the confirmed_flush backwards, as this could lead to
1042+
* data duplication issues caused by replicating already replicated
1043+
* changes.
1044+
*
1045+
* This can happen when a client acknowledges an LSN it doesn't have
1046+
* to do anything for, and thus didn't store persistently. After a
1047+
* restart, the client can send the prior LSN that it stored
1048+
* persistently as an acknowledgement, but we need to ignore such an
1049+
* LSN. See similar case handling in CreateDecodingContext.
1050+
*/
1051+
if (lsn>MyReplicationSlot->data.confirmed_flush)
1052+
MyReplicationSlot->data.confirmed_flush=lsn;
10411053

10421054
/* if we're past the location required for bumping xmin, do so */
10431055
if (MyReplicationSlot->candidate_xmin_lsn!=InvalidXLogRecPtr&&
@@ -1102,7 +1114,14 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
11021114
else
11031115
{
11041116
SpinLockAcquire(&MyReplicationSlot->mutex);
1105-
MyReplicationSlot->data.confirmed_flush=lsn;
1117+
1118+
/*
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* Prevent moving the confirmed_flush backwards. See comments above
1120+
* for the details.
1121+
*/
1122+
if (lsn>MyReplicationSlot->data.confirmed_flush)
1123+
MyReplicationSlot->data.confirmed_flush=lsn;
1124+
11061125
SpinLockRelease(&MyReplicationSlot->mutex);
11071126
}
11081127
}

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