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Commit7318f24

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 parent5355a24 commit7318f24

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‎src/backend/replication/logical/logical.c

Lines changed: 21 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1847,7 +1847,19 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
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SpinLockAcquire(&MyReplicationSlot->mutex);
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1850-
MyReplicationSlot->data.confirmed_flush=lsn;
1850+
/*
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* Prevent moving the confirmed_flush backwards, as this could lead to
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* data duplication issues caused by replicating already replicated
1853+
* changes.
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*
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* This can happen when a client acknowledges an LSN it doesn't have
1856+
* to do anything for, and thus didn't store persistently. After a
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* restart, the client can send the prior LSN that it stored
1858+
* persistently as an acknowledgement, but we need to ignore such an
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* LSN. See similar case handling in CreateDecodingContext.
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*/
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if (lsn>MyReplicationSlot->data.confirmed_flush)
1862+
MyReplicationSlot->data.confirmed_flush=lsn;
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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&&
@@ -1912,7 +1924,14 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
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else
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{
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SpinLockAcquire(&MyReplicationSlot->mutex);
1915-
MyReplicationSlot->data.confirmed_flush=lsn;
1927+
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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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*/
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if (lsn>MyReplicationSlot->data.confirmed_flush)
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MyReplicationSlot->data.confirmed_flush=lsn;
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SpinLockRelease(&MyReplicationSlot->mutex);
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}
19181937
}

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