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Prevent archive recovery from scanning non-existent WAL files.
Previously when there were multiple timelines listed in the history file of the recovery target timeline, archive recovery searched all of them, starting from the newest timeline to the oldest one, to find the segment to read. That is, archive recovery had to continuously fail scanning the segment until it reached the timeline that the segment belonged to. These scans for non-existent segment could be harmful on the recovery performance especially when archival area was located on the remote storage and each scan could take a long time. To address the issue, this commit changes archive recovery so that it skips scanning the timeline that the segment to read doesn't belong to. Author: Kyotaro Horiguchi, tweaked a bit by Fujii Masao Reviewed-by: David Steele, Pavel Suderevsky, Grigory Smolkin Discussion: https://postgr.es/m/16159-f5a34a3a04dc67e0@postgresql.org Discussion: 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

+26-1
Original file line numberDiff line numberDiff line change
@@ -3776,11 +3776,36 @@ XLogFileReadAnyTLI(XLogSegNo segno, int emode, XLogSource source)
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foreach(cell, tles)
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{
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TimeLineID tli = ((TimeLineHistoryEntry *) lfirst(cell))->tli;
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TimeLineHistoryEntry *hent = (TimeLineHistoryEntry *) lfirst(cell);
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TimeLineID tli = 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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/*
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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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*/
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if (hent->begin != InvalidXLogRecPtr)
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{
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XLogSegNo beginseg = 0;
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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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*/
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if (segno < beginseg)
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continue;
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}
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if (source == XLOG_FROM_ANY || source == XLOG_FROM_ARCHIVE)
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{
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fd = XLogFileRead(segno, emode, tli,

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