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Only WAL-log the modified portion in an UPDATE, if possible.

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When a row is updated, and the new tuple version is put on the same page as
the old one, only WAL-log the part of the new tuple that's not identical to
the old. This saves significantly on the amount of WAL that needs to be
written, in the common case that most fields are not modified.

Amit Kapila, with a lot of back and forth with me, Robert Haas, and others.
This commit is contained in:
Heikki Linnakangas
2014-03-12 22:46:04 +02:00
parent 17d787a3b1
commit a3115f0d9e
4 changed files with 285 additions and 65 deletions
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src/include/access/xlog.h
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@@ -279,6 +279,7 @@ typedef struct CheckpointStatsData
extern CheckpointStatsData CheckpointStats;
extern XLogRecPtr XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata);
extern bool XLogCheckBufferNeedsBackup(Buffer buffer);
extern void XLogFlush(XLogRecPtr RecPtr);
extern bool XLogBackgroundFlush(void);
extern bool XLogNeedsFlush(XLogRecPtr RecPtr);