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Commit4bd0ad9

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Prevent archive recovery from scanning non-existent WAL files.
Previously when there were multiple timelines listed in the history fileof the recovery target timeline, archive recovery searched all of them,starting from the newest timeline to the oldest one, to find the segmentto read. That is, archive recovery had to continuously fail scanningthe segment until it reached the timeline that the segment belonged to.These scans for non-existent segment could be harmful on the recoveryperformance especially when archival area was located on the remotestorage and each scan could take a long time.To address the issue, this commit changes archive recovery so thatit skips scanning the timeline that the segment to read doesn't belong to.Author: Kyotaro Horiguchi, tweaked a bit by Fujii MasaoReviewed-by: David Steele, Pavel Suderevsky, Grigory SmolkinDiscussion:https://postgr.es/m/16159-f5a34a3a04dc67e0@postgresql.orgDiscussion:https://postgr.es/m/20200129.120222.1476610231001551715.horikyota.ntt@gmail.com
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  • src/backend/access/transam

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‎src/backend/access/transam/xlog.c

Lines changed: 26 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3776,11 +3776,36 @@ XLogFileReadAnyTLI(XLogSegNo segno, int emode, XLogSource source)
37763776

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foreach(cell,tles)
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{
3779-
TimeLineIDtli= ((TimeLineHistoryEntry*)lfirst(cell))->tli;
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TimeLineHistoryEntry*hent= (TimeLineHistoryEntry*)lfirst(cell);
3780+
TimeLineIDtli=hent->tli;
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if (tli<curFileTLI)
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break;/* don't bother looking at too-old TLIs */
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3785+
/*
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* Skip scanning the timeline ID that the logfile segment to read
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* doesn't belong to
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*/
3789+
if (hent->begin!=InvalidXLogRecPtr)
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{
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XLogSegNobeginseg=0;
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3793+
XLByteToSeg(hent->begin,beginseg,wal_segment_size);
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/*
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* The logfile segment that doesn't belong to the timeline is
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* older or newer than the segment that the timeline started or
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* ended at, respectively. It's sufficient to check only the
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* starting segment of the timeline here. Since the timelines are
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* scanned in descending order in this loop, any segments newer
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* than the ending segment should belong to newer timeline and
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* have already been read before. So it's not necessary to check
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* the ending segment of the timeline here.
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*/
3805+
if (segno<beginseg)
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continue;
3807+
}
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37843809
if (source==XLOG_FROM_ANY||source==XLOG_FROM_ARCHIVE)
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{
37863811
fd=XLogFileRead(segno,emode,tli,

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