From: Tom Lane Date: Thu, 24 Aug 2006 01:18:34 +0000 (+0000) Subject: Optimize the case where a btree indexscan has current and mark positions X-Git-Url: http://waps.l3s.uni-hannover.de/gitweb/?a=commitdiff_plain;h=d78ea3539fbbfdca3552367757db485e057e5df2;p=users%2Fbernd%2Fpostgres.git 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 --- diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c index 57e3154c13..0f3c595696 100644 --- a/src/backend/access/nbtree/nbtree.c +++ b/src/backend/access/nbtree/nbtree.c @@ -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; - } - - /* bump pin on marked buffer */ - if (BTScanPosIsValid(so->markPos)) + /* + * The mark position is on the same page we are currently on. + * Just restore the itemIndex. + */ + so->currPos.itemIndex = so->markItemIndex; + } + else { - IncrBufferRefCount(so->markPos.buf); - memcpy(&so->currPos, &so->markPos, - offsetof(BTScanPosData, items[1]) + - so->markPos.lastItem * sizeof(BTScanPosItem)); + /* 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; + } + + 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(); diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c index 97a1ae466b..84077baf18 100644 --- a/src/backend/access/nbtree/nbtsearch.c +++ b/src/backend/access/nbtree/nbtsearch.c @@ -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. diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h index 77a4ed1304..3c5c4cd2ef 100644 --- a/src/include/access/nbtree.h +++ b/src/include/access/nbtree.h @@ -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 */