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Commite6c44ee

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Fix off-by-one possibly leading to skipped XLOG_RUNNING_XACTS records.
Since6ef2eba ("Skip checkpoints, archiving on idle systems."),GetLastImportantRecPtr() is used to avoid performing superfluouscheckpoints, xlog switches, running-xact records when the system isidle. Unfortunately the check concerning running-xact records had aoff-by-one error, leading to such records being potentially skippedwhen only a single record has been inserted since the lastrunning-xact record.An alternative approach would have been to changeGetLastImportantRecPtr()'s definition to point to the end of records,but that would make the checkpoint code more complicated.Author: Andres FreundDiscussion:https://postgr.es/m/20170505012447.wsrympaxnfis6ojt@alap3.anarazel.deBackpatch: no, code only present in master
1 parent334b82c commite6c44ee

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2 files changed

+7
-3
lines changed

2 files changed

+7
-3
lines changed

‎src/backend/postmaster/bgwriter.c

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -325,10 +325,13 @@ BackgroundWriterMain(void)
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/*
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* Only log if enough time has passed and interesting records have
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* been inserted since the last snapshot.
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* been inserted since the last snapshot. Have to compare with <=
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* instead of < because GetLastImportantRecPtr() points at the
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* start of a record, whereas last_snapshot_lsn points just past
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* the end of the record.
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*/
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if (now >=timeout&&
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last_snapshot_lsn<GetLastImportantRecPtr())
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last_snapshot_lsn <=GetLastImportantRecPtr())
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{
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last_snapshot_lsn=LogStandbySnapshot();
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last_snapshot_ts=now;

‎src/backend/postmaster/checkpointer.c

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -611,7 +611,8 @@ CheckArchiveTimeout(void)
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{
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/*
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* Switch segment only when "important" WAL has been logged since the
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* last segment switch.
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* last segment switch (last_switch_lsn points to end of segment
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* switch occurred in).
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*/
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if (GetLastImportantRecPtr()>last_switch_lsn)
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{

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