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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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33
src/backend/access/nbtree/nbtree.c
View File

@ -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();
}
@ -477,6 +481,16 @@ btrestrpos(PG_FUNCTION_ARGS)
IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
BTScanOpaque so = (BTScanOpaque) scan->opaque;
if (so->markItemIndex >= 0)
{
/*
* 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))
{
@ -488,14 +502,15 @@ btrestrpos(PG_FUNCTION_ARGS)
so->currPos.buf = InvalidBuffer;
}
/* bump pin on marked buffer */
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();
}

19
src/backend/access/nbtree/nbtsearch.c
View File

@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.105 2006/05/07 01:21:30 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.106 2006/08/24 01:18:34 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -815,6 +815,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
so->currPos.moreRight = false;
}
so->numKilled = 0; /* just paranoia */
so->markItemIndex = -1; /* ditto */
/* position to the precise item on the page */
offnum = _bt_binsrch(rel, buf, keysCount, scankeys, nextkey);
@ -1053,6 +1054,21 @@ _bt_steppage(IndexScanDesc scan, ScanDirection dir)
if (so->numKilled > 0)
_bt_killitems(scan, true);
/*
* Before we modify currPos, make a copy of the page data if there
* was a mark position that needs it.
*/
if (so->markItemIndex >= 0)
{
/* bump pin on current buffer for assignment to mark buffer */
IncrBufferRefCount(so->currPos.buf);
memcpy(&so->markPos, &so->currPos,
offsetof(BTScanPosData, items[1]) +
so->currPos.lastItem * sizeof(BTScanPosItem));
so->markPos.itemIndex = so->markItemIndex;
so->markItemIndex = -1;
}
rel = scan->indexRelation;
if (ScanDirectionIsForward(dir))
@ -1408,6 +1424,7 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
so->currPos.moreRight = false;
}
so->numKilled = 0; /* just paranoia */
so->markItemIndex = -1; /* ditto */
/*
* Now load data from the first page of the scan.

11
src/include/access/nbtree.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.103 2006/08/07 16:57:57 tgl Exp $
* $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.104 2006/08/24 01:18:34 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -438,6 +438,15 @@ typedef struct BTScanOpaqueData
int *killedItems; /* currPos.items indexes of killed items */
int numKilled; /* number of currently stored items */
/*
* If the marked position is on the same page as current position,
* we don't use markPos, but just keep the marked itemIndex in
* markItemIndex (all the rest of currPos is valid for the mark position).
* Hence, to determine if there is a mark, first look at markItemIndex,
* then at markPos.
*/
int markItemIndex; /* itemIndex, or -1 if not valid */
/* keep these last in struct for efficiency */
BTScanPosData currPos; /* current position data */
BTScanPosData markPos; /* marked position, if any */