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Commitc0f51fd

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
1 parent253cf66 commitc0f51fd

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‎src/backend/replication/logical/logical.c

Lines changed: 21 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1830,7 +1830,19 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
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18311831
SpinLockAcquire(&MyReplicationSlot->mutex);
18321832

1833-
MyReplicationSlot->data.confirmed_flush=lsn;
1833+
/*
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* Prevent moving the confirmed_flush backwards, as this could lead to
1835+
* data duplication issues caused by replicating already replicated
1836+
* changes.
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*
1838+
* This can happen when a client acknowledges an LSN it doesn't have
1839+
* to do anything for, and thus didn't store persistently. After a
1840+
* restart, the client can send the prior LSN that it stored
1841+
* persistently as an acknowledgement, but we need to ignore such an
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* LSN. See similar case handling in CreateDecodingContext.
1843+
*/
1844+
if (lsn>MyReplicationSlot->data.confirmed_flush)
1845+
MyReplicationSlot->data.confirmed_flush=lsn;
18341846

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/* if we're past the location required for bumping xmin, do so */
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if (MyReplicationSlot->candidate_xmin_lsn!=InvalidXLogRecPtr&&
@@ -1895,7 +1907,14 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
18951907
else
18961908
{
18971909
SpinLockAcquire(&MyReplicationSlot->mutex);
1898-
MyReplicationSlot->data.confirmed_flush=lsn;
1910+
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/*
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* Prevent moving the confirmed_flush backwards. See comments above
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* for the details.
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*/
1915+
if (lsn>MyReplicationSlot->data.confirmed_flush)
1916+
MyReplicationSlot->data.confirmed_flush=lsn;
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SpinLockRelease(&MyReplicationSlot->mutex);
19001919
}
19011920
}

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