Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commitef92b82

Browse files
committed
Further cleanup in _bt_first: eliminate duplicate code paths.
1 parent550d347 commitef92b82

File tree

1 file changed

+70
-99
lines changed

1 file changed

+70
-99
lines changed

‎src/backend/access/nbtree/nbtsearch.c‎

Lines changed: 70 additions & 99 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.85 2003/12/2103:00:04 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.86 2003/12/2117:52:34 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -496,6 +496,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
496496
StrategyNumberstrat;
497497
boolres;
498498
boolnextkey;
499+
boolgoback;
499500
boolcontinuescan;
500501
ScanKeyscankeys;
501502
ScanKey*startKeys=NULL;
@@ -695,18 +696,41 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
695696
pfree(startKeys);
696697

697698
/*
698-
* We want to locate either the first item >= boundary point, or
699-
* first item > boundary point, depending on the initial-positioning
700-
* strategy we just chose.
699+
* Examine the selected initial-positioning strategy to determine
700+
* exactly where we need to start the scan, and set flag variables
701+
* to control the code below.
702+
*
703+
* If nextkey = false, _bt_search and _bt_binsrch will locate the
704+
* first item >= scan key. If nextkey = true, they will locate the
705+
* first item > scan key.
706+
*
707+
* If goback = true, we will then step back one item, while if
708+
* goback = false, we will start the scan on the located item.
709+
*
710+
* it's yet other place to add some code later for is(not)null ...
701711
*/
702712
switch (strat_total)
703713
{
704714
caseBTLessStrategyNumber:
715+
/*
716+
* Find first item >= scankey, then back up one to arrive at last
717+
* item < scankey. (Note: this positioning strategy is only used
718+
* for a backward scan, so that is always the correct starting
719+
* position.)
720+
*/
705721
nextkey= false;
722+
goback= true;
706723
break;
707724

708725
caseBTLessEqualStrategyNumber:
726+
/*
727+
* Find first item > scankey, then back up one to arrive at last
728+
* item <= scankey. (Note: this positioning strategy is only used
729+
* for a backward scan, so that is always the correct starting
730+
* position.)
731+
*/
709732
nextkey= true;
733+
goback= true;
710734
break;
711735

712736
caseBTEqualStrategyNumber:
@@ -715,17 +739,41 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
715739
* equal item not first one.
716740
*/
717741
if (ScanDirectionIsBackward(dir))
742+
{
743+
/*
744+
* This is the same as the <= strategy. We will check
745+
* at the end whether the found item is actually =.
746+
*/
718747
nextkey= true;
748+
goback= true;
749+
}
719750
else
751+
{
752+
/*
753+
* This is the same as the >= strategy. We will check
754+
* at the end whether the found item is actually =.
755+
*/
720756
nextkey= false;
757+
goback= false;
758+
}
721759
break;
722760

723761
caseBTGreaterEqualStrategyNumber:
762+
/*
763+
* Find first item >= scankey. (This is only used for
764+
* forward scans.)
765+
*/
724766
nextkey= false;
767+
goback= false;
725768
break;
726769

727770
caseBTGreaterStrategyNumber:
771+
/*
772+
* Find first item > scankey. (This is only used for
773+
* forward scans.)
774+
*/
728775
nextkey= true;
776+
goback= false;
729777
break;
730778

731779
default:
@@ -756,21 +804,18 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
756804

757805
/* remember which buffer we have pinned */
758806
so->btso_curbuf=buf;
759-
blkno=BufferGetBlockNumber(buf);
760-
page=BufferGetPage(buf);
761807

762808
/* position to the precise item on the page */
763809
offnum=_bt_binsrch(rel,buf,keysCount,scankeys,nextkey);
764810

811+
page=BufferGetPage(buf);
812+
blkno=BufferGetBlockNumber(buf);
765813
ItemPointerSet(current,blkno,offnum);
766814

767815
/* done with manufactured scankey, now */
768816
pfree(scankeys);
769817

770818
/*
771-
* It's now time to examine the initial-positioning strategy to find the
772-
* exact place to start the scan.
773-
*
774819
* If nextkey = false, we are positioned at the first item >= scan key,
775820
* or possibly at the end of a page on which all the existing items are
776821
* less than the scan key and we know that everything on later pages
@@ -781,103 +826,29 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
781826
* less than or equal to the scan key and we know that everything on
782827
* later pages is greater than scan key.
783828
*
784-
* The actually desired starting point is either this item oran adjacent
785-
* one, or in the end-of-page case it's thelast item onthis page or
786-
* thefirst item onthe next. We apply _bt_step if needed to get to
829+
* The actually desired starting point is either this item orthe prior
830+
* one, or in the end-of-page case it's thefirst item onthe next page
831+
*orthelast item onthis page. We apply _bt_step if needed to get to
787832
* the right place.
788833
*
789-
*Note: if _bt_step fails (meaning we fell off the end of the index in
834+
*If _bt_step fails (meaning we fell off the end of the index in
790835
* one direction or the other), then there are no matches so we just
791836
* return false.
792-
*
793-
* it's yet other place to add some code later for is(not)null ...
794837
*/
795-
switch (strat_total)
838+
if (goback)
796839
{
797-
caseBTLessStrategyNumber:
798-
799-
/*
800-
* We are on first item >= scankey.
801-
*
802-
* Back up one to arrive at last item < scankey. (Note: this
803-
* positioning strategy is only used for a backward scan, so
804-
* that is always the correct starting position.)
805-
*/
806-
if (!_bt_step(scan,&buf,BackwardScanDirection))
807-
return false;
808-
break;
809-
810-
caseBTLessEqualStrategyNumber:
811-
812-
/*
813-
* We are on first item > scankey.
814-
*
815-
* Back up one to arrive at last item <= scankey. (Note: this
816-
* positioning strategy is only used for a backward scan, so
817-
* that is always the correct starting position.)
818-
*/
819-
if (!_bt_step(scan,&buf,BackwardScanDirection))
840+
/* _bt_step will do the right thing if we are at end-of-page */
841+
if (!_bt_step(scan,&buf,BackwardScanDirection))
842+
return false;
843+
}
844+
else
845+
{
846+
/* If we're at end-of-page, must step forward to next page */
847+
if (offnum>PageGetMaxOffsetNumber(page))
848+
{
849+
if (!_bt_step(scan,&buf,ForwardScanDirection))
820850
return false;
821-
break;
822-
823-
caseBTEqualStrategyNumber:
824-
/*
825-
* If a backward scan was specified, need to start with last
826-
* equal item not first one.
827-
*/
828-
if (ScanDirectionIsBackward(dir))
829-
{
830-
/*
831-
* We are on first item > scankey.
832-
*
833-
* Back up one to arrive at last item <= scankey.
834-
* We will check below to see if it is equal to scankey.
835-
*/
836-
if (!_bt_step(scan,&buf,BackwardScanDirection))
837-
return false;
838-
}
839-
else
840-
{
841-
/*
842-
* We are on first item >= scankey.
843-
*
844-
* Make sure we are on a real item; might have to
845-
* step forward if currently at end of page.
846-
* We will check below to see if it is equal to scankey.
847-
*/
848-
if (offnum>PageGetMaxOffsetNumber(page))
849-
{
850-
if (!_bt_step(scan,&buf,ForwardScanDirection))
851-
return false;
852-
}
853-
}
854-
break;
855-
856-
caseBTGreaterEqualStrategyNumber:
857-
858-
/*
859-
* We want the first item >= scankey, which is where we are...
860-
* unless we're not anywhere at all...
861-
*/
862-
if (offnum>PageGetMaxOffsetNumber(page))
863-
{
864-
if (!_bt_step(scan,&buf,ForwardScanDirection))
865-
return false;
866-
}
867-
break;
868-
869-
caseBTGreaterStrategyNumber:
870-
871-
/*
872-
* We want the first item > scankey, which is where we are...
873-
* unless we're not anywhere at all...
874-
*/
875-
if (offnum>PageGetMaxOffsetNumber(page))
876-
{
877-
if (!_bt_step(scan,&buf,ForwardScanDirection))
878-
return false;
879-
}
880-
break;
851+
}
881852
}
882853

883854
/* okay, current item pointer for the scan is right */

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp