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Optimize the case where a btree indexscan has current and mark positions

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on the same index page; we can avoid data copying as well as buffer refcount
manipulations in this common case.  Makes for a small but noticeable
improvement in mergejoin speed.

Heikki Linnakangas
This commit is contained in:
Tom Lane
2006-08-24 01:18:34 +00:00
parent 7ad642d0b5
commit 08ae5edc5c
3 changed files with 67 additions and 26 deletions
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63
src/backend/access/nbtree/nbtree.c
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@@ -12,7 +12,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.149 2006/05/10 23:18:39 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.150 2006/08/24 01:18:34 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -392,6 +392,7 @@ btrescan(PG_FUNCTION_ARGS)
ReleaseBuffer(so->markPos.buf);
so->markPos.buf = InvalidBuffer;
}
so->markItemIndex = -1;
/*
* Reset the scan keys. Note that keys ordering stuff moved to _bt_first.
@@ -430,6 +431,7 @@ btendscan(PG_FUNCTION_ARGS)
ReleaseBuffer(so->markPos.buf);
so->markPos.buf = InvalidBuffer;
}
so->markItemIndex = -1;
if (so->killedItems != NULL)
pfree(so->killedItems);
@@ -456,14 +458,16 @@ btmarkpos(PG_FUNCTION_ARGS)
so->markPos.buf = InvalidBuffer;
}
/* bump pin on current buffer for assignment to mark buffer */
/*
* Just record the current itemIndex. If we later step to next page
* before releasing the marked position, _bt_steppage makes a full copy
* of the currPos struct in markPos. If (as often happens) the mark is
* moved before we leave the page, we don't have to do that work.
*/
if (BTScanPosIsValid(so->currPos))
{
IncrBufferRefCount(so->currPos.buf);
memcpy(&so->markPos, &so->currPos,
offsetof(BTScanPosData, items[1]) +
so->currPos.lastItem * sizeof(BTScanPosItem));
}
so->markItemIndex = so->currPos.itemIndex;
else
so->markItemIndex = -1;
PG_RETURN_VOID();
}
@@ -477,24 +481,35 @@ btrestrpos(PG_FUNCTION_ARGS)
IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
BTScanOpaque so = (BTScanOpaque) scan->opaque;
/* we aren't holding any read locks, but gotta drop the pin */
if (BTScanPosIsValid(so->currPos))
if (so->markItemIndex >= 0)
{
/* Before leaving current page, deal with any killed items */
if (so->numKilled > 0 &&
so->currPos.buf != so->markPos.buf)
_bt_killitems(scan, false);
ReleaseBuffer(so->currPos.buf);
so->currPos.buf = InvalidBuffer;
}
/*
* The mark position is on the same page we are currently on.
* Just restore the itemIndex.
*/
so->currPos.itemIndex = so->markItemIndex;
}
else
{
/* we aren't holding any read locks, but gotta drop the pin */
if (BTScanPosIsValid(so->currPos))
{
/* Before leaving current page, deal with any killed items */
if (so->numKilled > 0 &&
so->currPos.buf != so->markPos.buf)
_bt_killitems(scan, false);
ReleaseBuffer(so->currPos.buf);
so->currPos.buf = InvalidBuffer;
}
/* bump pin on marked buffer */
if (BTScanPosIsValid(so->markPos))
{
IncrBufferRefCount(so->markPos.buf);
memcpy(&so->currPos, &so->markPos,
offsetof(BTScanPosData, items[1]) +
so->markPos.lastItem * sizeof(BTScanPosItem));
if (BTScanPosIsValid(so->markPos))
{
/* bump pin on mark buffer for assignment to current buffer */
IncrBufferRefCount(so->markPos.buf);
memcpy(&so->currPos, &so->markPos,
offsetof(BTScanPosData, items[1]) +
so->markPos.lastItem * sizeof(BTScanPosItem));
}
}
PG_RETURN_VOID();