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Keep heavily-contended fields in XLogCtlInsert on different cache lines.

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Performance testing shows that if the insertpos_lck spinlock and the fields
that it protects are on the same cache line with other variables that are
frequently accessed, the false sharing can hurt performance a lot. Keep
them apart by adding some padding.
This commit is contained in:
Heikki Linnakangas
2013-09-04 23:14:33 +03:00
parent cc52d5b33f
commit 375d8526f2
2 changed files with 23 additions and 3 deletions
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15
src/backend/access/transam/xlog.c
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@ -408,7 +408,7 @@ typedef struct
typedef union XLogInsertSlotPadded
{
XLogInsertSlot slot;
char pad[64];
char pad[CACHE_LINE_SIZE];
} XLogInsertSlotPadded;
/*
@ -428,8 +428,14 @@ typedef struct XLogCtlInsert
uint64 CurrBytePos;
uint64 PrevBytePos;
/* insertion slots, see above for details */
XLogInsertSlotPadded *insertSlots;
/*
* Make sure the above heavily-contended spinlock and byte positions are
* on their own cache line. In particular, the RedoRecPtr and full page
* write variables below should be on a different cache line. They are
* read on every WAL insertion, but updated rarely, and we don't want
* those reads to steal the cache line containing Curr/PrevBytePos.
*/
char pad[CACHE_LINE_SIZE];
/*
* fullPageWrites is the master copy used by all backends to determine
@ -455,6 +461,9 @@ typedef struct XLogCtlInsert
bool exclusiveBackup;
int nonExclusiveBackups;
XLogRecPtr lastBackupStart;
/* insertion slots, see XLogInsertSlot struct above for details */
XLogInsertSlotPadded *insertSlots;
} XLogCtlInsert;
/*