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Optimize the case where a btree indexscan has current and mark positions
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
parent
7ad642d0b5
commit
08ae5edc5c
@ -12,7 +12,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.149 2006/05/10 23:18:39 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.150 2006/08/24 01:18:34 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -392,6 +392,7 @@ btrescan(PG_FUNCTION_ARGS)
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ReleaseBuffer(so->markPos.buf);
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so->markPos.buf = InvalidBuffer;
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}
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so->markItemIndex = -1;
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/*
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* Reset the scan keys. Note that keys ordering stuff moved to _bt_first.
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@ -430,6 +431,7 @@ btendscan(PG_FUNCTION_ARGS)
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ReleaseBuffer(so->markPos.buf);
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so->markPos.buf = InvalidBuffer;
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}
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so->markItemIndex = -1;
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if (so->killedItems != NULL)
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pfree(so->killedItems);
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@ -456,14 +458,16 @@ btmarkpos(PG_FUNCTION_ARGS)
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so->markPos.buf = InvalidBuffer;
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}
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/* bump pin on current buffer for assignment to mark buffer */
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/*
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* Just record the current itemIndex. If we later step to next page
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* before releasing the marked position, _bt_steppage makes a full copy
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* of the currPos struct in markPos. If (as often happens) the mark is
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* moved before we leave the page, we don't have to do that work.
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*/
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if (BTScanPosIsValid(so->currPos))
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{
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IncrBufferRefCount(so->currPos.buf);
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memcpy(&so->markPos, &so->currPos,
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offsetof(BTScanPosData, items[1]) +
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so->currPos.lastItem * sizeof(BTScanPosItem));
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}
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so->markItemIndex = so->currPos.itemIndex;
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else
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so->markItemIndex = -1;
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PG_RETURN_VOID();
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}
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@ -477,24 +481,35 @@ btrestrpos(PG_FUNCTION_ARGS)
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IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
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BTScanOpaque so = (BTScanOpaque) scan->opaque;
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/* we aren't holding any read locks, but gotta drop the pin */
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if (BTScanPosIsValid(so->currPos))
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if (so->markItemIndex >= 0)
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{
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/* Before leaving current page, deal with any killed items */
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if (so->numKilled > 0 &&
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so->currPos.buf != so->markPos.buf)
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_bt_killitems(scan, false);
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ReleaseBuffer(so->currPos.buf);
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so->currPos.buf = InvalidBuffer;
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}
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/*
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* The mark position is on the same page we are currently on.
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* Just restore the itemIndex.
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*/
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so->currPos.itemIndex = so->markItemIndex;
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}
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else
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{
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/* we aren't holding any read locks, but gotta drop the pin */
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if (BTScanPosIsValid(so->currPos))
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{
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/* Before leaving current page, deal with any killed items */
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if (so->numKilled > 0 &&
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so->currPos.buf != so->markPos.buf)
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_bt_killitems(scan, false);
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ReleaseBuffer(so->currPos.buf);
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so->currPos.buf = InvalidBuffer;
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}
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/* bump pin on marked buffer */
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if (BTScanPosIsValid(so->markPos))
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{
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IncrBufferRefCount(so->markPos.buf);
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memcpy(&so->currPos, &so->markPos,
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offsetof(BTScanPosData, items[1]) +
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so->markPos.lastItem * sizeof(BTScanPosItem));
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if (BTScanPosIsValid(so->markPos))
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{
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/* bump pin on mark buffer for assignment to current buffer */
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IncrBufferRefCount(so->markPos.buf);
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memcpy(&so->currPos, &so->markPos,
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offsetof(BTScanPosData, items[1]) +
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so->markPos.lastItem * sizeof(BTScanPosItem));
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}
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}
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PG_RETURN_VOID();
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@ -8,7 +8,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.105 2006/05/07 01:21:30 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.106 2006/08/24 01:18:34 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -815,6 +815,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
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so->currPos.moreRight = false;
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}
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so->numKilled = 0; /* just paranoia */
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so->markItemIndex = -1; /* ditto */
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/* position to the precise item on the page */
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offnum = _bt_binsrch(rel, buf, keysCount, scankeys, nextkey);
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@ -1053,6 +1054,21 @@ _bt_steppage(IndexScanDesc scan, ScanDirection dir)
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if (so->numKilled > 0)
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_bt_killitems(scan, true);
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/*
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* Before we modify currPos, make a copy of the page data if there
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* was a mark position that needs it.
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*/
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if (so->markItemIndex >= 0)
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{
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/* bump pin on current buffer for assignment to mark buffer */
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IncrBufferRefCount(so->currPos.buf);
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memcpy(&so->markPos, &so->currPos,
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offsetof(BTScanPosData, items[1]) +
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so->currPos.lastItem * sizeof(BTScanPosItem));
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so->markPos.itemIndex = so->markItemIndex;
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so->markItemIndex = -1;
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}
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rel = scan->indexRelation;
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if (ScanDirectionIsForward(dir))
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@ -1408,6 +1424,7 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
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so->currPos.moreRight = false;
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}
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so->numKilled = 0; /* just paranoia */
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so->markItemIndex = -1; /* ditto */
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/*
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* Now load data from the first page of the scan.
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@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.103 2006/08/07 16:57:57 tgl Exp $
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* $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.104 2006/08/24 01:18:34 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -438,6 +438,15 @@ typedef struct BTScanOpaqueData
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int *killedItems; /* currPos.items indexes of killed items */
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int numKilled; /* number of currently stored items */
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/*
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* If the marked position is on the same page as current position,
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* we don't use markPos, but just keep the marked itemIndex in
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* markItemIndex (all the rest of currPos is valid for the mark position).
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* Hence, to determine if there is a mark, first look at markItemIndex,
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* then at markPos.
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*/
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int markItemIndex; /* itemIndex, or -1 if not valid */
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/* keep these last in struct for efficiency */
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BTScanPosData currPos; /* current position data */
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BTScanPosData markPos; /* marked position, if any */
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