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Commitb8b69d8

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Revert "Reduce checkpoints and WAL traffic on low activity database server"
This reverts commit18fb9d8. Perdiscussion, it does not seem like a good idea to allow committed changes togo un-checkpointed indefinitely, as could happen in a low-traffic server;that makes us entirely reliant on the WAL stream with no redundancy thatmight aid data recovery in case of disk failure.This re-introduces the original problem of hot-standby setups generating asmall continuing stream of WAL traffic even when idle, but there are otherways to address that without compromising crash recovery, so we'll revisitthat issue in a future release cycle.
1 parent8b23db9 commitb8b69d8

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+13
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  • src/backend/access/transam

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+13
-15
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 13 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -7646,10 +7646,6 @@ CreateCheckPoint(int flags)
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uint32freespace;
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uint32_logId;
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uint32_logSeg;
7649-
uint32redo_logId;
7650-
uint32redo_logSeg;
7651-
uint32insert_logId;
7652-
uint32insert_logSeg;
76537649
TransactionId*inCommitXids;
76547650
intnInCommit;
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@@ -7726,31 +7722,33 @@ CreateCheckPoint(int flags)
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LWLockAcquire(WALInsertLock,LW_EXCLUSIVE);
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/*
7729-
* If this isn't a shutdown or forced checkpoint, and we have notswitched
7730-
*to the next WAL file since the start of the last checkpoint, skip the
7725+
* If this isn't a shutdown or forced checkpoint, and we have notinserted
7726+
*any XLOG records since the start of the last checkpoint, skip the
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* checkpoint.The idea here is to avoid inserting duplicate checkpoints
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* when the system is idle. That wastes log space, and more importantly it
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* exposes us to possible loss of both current and previous checkpoint
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* records if the machine crashes just as we're writing the update.
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* (Perhaps it'd make even more sense to checkpoint only when the previous
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* checkpoint record is in a different xlog page?)
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*
7738-
* While holding the WALInsertLock we find the current WAL insertion point
7739-
* and compare that with the starting point of the last checkpoint, which
7740-
* is the redo pointer. We use the redo pointer because the start and end
7741-
* points of a checkpoint can be hundreds of files apart on large systems
7742-
* when checkpoint writes are spread out over time.
7734+
* We have to make two tests to determine that nothing has happened since
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* the start of the last checkpoint: current insertion point must match
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* the end of the last checkpoint record, and its redo pointer must point
7737+
* to itself.
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*/
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if ((flags& (CHECKPOINT_IS_SHUTDOWN |CHECKPOINT_END_OF_RECOVERY |
77457740
CHECKPOINT_FORCE))==0)
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{
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XLogRecPtrcurInsert;
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77497744
INSERT_RECPTR(curInsert,Insert,Insert->curridx);
7750-
XLByteToSeg(curInsert,insert_logId,insert_logSeg);
7751-
XLByteToSeg(ControlFile->checkPointCopy.redo,redo_logId,redo_logSeg);
7752-
if (insert_logId==redo_logId&&
7753-
insert_logSeg==redo_logSeg)
7745+
if (curInsert.xlogid==ControlFile->checkPoint.xlogid&&
7746+
curInsert.xrecoff==ControlFile->checkPoint.xrecoff+
7747+
MAXALIGN(SizeOfXLogRecord+sizeof(CheckPoint))&&
7748+
ControlFile->checkPoint.xlogid==
7749+
ControlFile->checkPointCopy.redo.xlogid&&
7750+
ControlFile->checkPoint.xrecoff==
7751+
ControlFile->checkPointCopy.redo.xrecoff)
77547752
{
77557753
LWLockRelease(WALInsertLock);
77567754
LWLockRelease(CheckpointLock);

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