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Go back to considering HOT on pages marked full.

Commit2fd8685 simplified the checking of modified attributes thattakes place within heap_update(). This included a micro-optimizationaffecting pages marked PD_PAGE_FULL: don't even try to use HOT to save afew cycles on determining HOT safety. The assumption was that it won'twork out this time around, since it can't have worked out last timearound.Remove the micro-optimization. It could only ever save cycles that areconsumed by the vast majority of heap_update() calls, which hardly seemsworth the added complexity. It also seems quite possible that there areworkloads that will do worse over time by repeated application of themicro-optimization, despite saving some cycles on average, in the shortterm.Author: Peter Geoghegan <pg@bowt.ie>Reviewed-By: Álvaro Herrera <alvherre@alvh.no-ip.org>Discussion:https://postgr.es/m/CAH2-WznU1L3+DMPr1F7o2eJBT7=3bAJoY6ZkWABAxNt+-afyTA@mail.gmail.com

1 parentdd484c9 commit1a6f5a0Copy full SHA for 1a6f5a0

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src/backend/access/heap
- heapam.c

1 file changed

-25

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`‎src/backend/access/heap/heapam.c`

Lines changed: 6 additions & 25 deletions

Original file line number	Diff line number	Diff line change
`@@ -3179,7 +3179,6 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,`
`3179`	`3179`	`boolhave_tuple_lock= false;`
`3180`	`3180`	`booliscombo;`
`3181`	`3181`	`booluse_hot_update= false;`
`3182`		`-boolhot_attrs_checked= false;`
`3183`	`3182`	`boolkey_intact;`
`3184`	`3183`	`boolall_visible_cleared= false;`
`3185`	`3184`	`boolall_visible_cleared_new= false;`
`@@ -3228,32 +3227,15 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,`
`3228`	`3227`	`key_attrs=RelationGetIndexAttrBitmap(relation,INDEX_ATTR_BITMAP_KEY);`
`3229`	`3228`	`id_attrs=RelationGetIndexAttrBitmap(relation,`
`3230`	`3229`	`INDEX_ATTR_BITMAP_IDENTITY_KEY);`
`3231`		`-`
	`3230`	`+interesting_attrs=NULL;`
	`3231`	`+interesting_attrs=bms_add_members(interesting_attrs,hot_attrs);`
	`3232`	`+interesting_attrs=bms_add_members(interesting_attrs,key_attrs);`
	`3233`	`+interesting_attrs=bms_add_members(interesting_attrs,id_attrs);`
`3232`	`3234`
`3233`	`3235`	`block=ItemPointerGetBlockNumber(otid);`
`3234`	`3236`	`buffer=ReadBuffer(relation,block);`
`3235`	`3237`	`page=BufferGetPage(buffer);`
`3236`	`3238`
`3237`		`-interesting_attrs=NULL;`
`3238`		`-`
`3239`		`-/*`
`3240`		`- * If the page is already full, there is hardly any chance of doing a HOT`
`3241`		`- * update on this page. It might be wasteful effort to look for index`
`3242`		`- * column updates only to later reject HOT updates for lack of space in`
`3243`		`- * the same page. So we be conservative and only fetch hot_attrs if the`
`3244`		`- * page is not already full. Since we are already holding a pin on the`
`3245`		`- * buffer, there is no chance that the buffer can get cleaned up`
`3246`		`- * concurrently and even if that was possible, in the worst case we lose a`
`3247`		`- * chance to do a HOT update.`
`3248`		`- */`
`3249`		`-if (!PageIsFull(page))`
`3250`		`-{`
`3251`		`-interesting_attrs=bms_add_members(interesting_attrs,hot_attrs);`
`3252`		`-hot_attrs_checked= true;`
`3253`		`-}`
`3254`		`-interesting_attrs=bms_add_members(interesting_attrs,key_attrs);`
`3255`		`-interesting_attrs=bms_add_members(interesting_attrs,id_attrs);`
`3256`		`-`
`3257`	`3239`	`/*`
`3258`	`3240`	`* Before locking the buffer, pin the visibility map page if it appears to`
`3259`	`3241`	`* be necessary. Since we haven't got the lock yet, someone else might be`
`@@ -3867,10 +3849,9 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,`
`3867`	`3849`	`/*`
`3868`	`3850`	`* Since the new tuple is going into the same page, we might be able`
`3869`	`3851`	`* to do a HOT update. Check if any of the index columns have been`
`3870`		`- * changed. If the page was already full, we may have skipped checking`
`3871`		`- * for index columns, and also can't do a HOT update.`
	`3852`	`+ * changed.`
`3872`	`3853`	`*/`
`3873`		`-if (hot_attrs_checked&&!bms_overlap(modified_attrs,hot_attrs))`
	`3854`	`+if (!bms_overlap(modified_attrs,hot_attrs))`
`3874`	`3855`	`use_hot_update= true;`
`3875`	`3856`	`}`
`3876`	`3857`	`else`

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Commit1a6f5a0

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`‎src/backend/access/heap/heapam.c`

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