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Commit916b232

Browse files
committed
Clean up and document btree code for ordering keys. Neat stuff,
actually, but who could understand it with no comments? Fix bugwhile at it: _bt_orderkeys would try to invoke comparisons onNULL inputs, given the right sort of redundant quals.
1 parentda1ad32 commit916b232

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3 files changed

+284
-191
lines changed

3 files changed

+284
-191
lines changed

‎src/backend/access/nbtree/nbtsearch.c

Lines changed: 50 additions & 53 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-
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.61 2000/07/21 06:42:32 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.62 2000/07/25 04:47:58 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -374,7 +374,7 @@ _bt_next(IndexScanDesc scan, ScanDirection dir)
374374
BTItembtitem;
375375
IndexTupleitup;
376376
BTScanOpaqueso;
377-
Sizekeysok;
377+
boolcontinuescan;
378378

379379
rel=scan->relation;
380380
so= (BTScanOpaque)scan->opaque;
@@ -396,16 +396,14 @@ _bt_next(IndexScanDesc scan, ScanDirection dir)
396396
btitem= (BTItem)PageGetItem(page,PageGetItemId(page,offnum));
397397
itup=&btitem->bti_itup;
398398

399-
if (_bt_checkkeys(scan,itup,&keysok))
399+
if (_bt_checkkeys(scan,itup,dir,&continuescan))
400400
{
401401
/* tuple passes all scan key conditions, so return it */
402-
Assert(keysok==so->numberOfKeys);
403402
returnFormRetrieveIndexResult(current,&(itup->t_tid));
404403
}
405404

406405
/* This tuple doesn't pass, but there might be more that do */
407-
}while (keysok >=so->numberOfFirstKeys||
408-
(keysok== ((Size)-1)&&ScanDirectionIsBackward(dir)));
406+
}while (continuescan);
409407

410408
/* No more items, so close down the current-item info */
411409
ItemPointerSetInvalid(current);
@@ -442,11 +440,10 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
442440
RegProcedureproc;
443441
int32result;
444442
BTScanOpaqueso;
445-
Sizekeysok;
446-
boolstrategyCheck;
447-
ScanKeyscankeys=0;
443+
boolcontinuescan;
444+
ScanKeyscankeys=NULL;
448445
intkeysCount=0;
449-
int*nKeyIs=0;
446+
int*nKeyIs=NULL;
450447
inti,
451448
j;
452449
StrategyNumberstrat_total;
@@ -455,71 +452,74 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
455452
so= (BTScanOpaque)scan->opaque;
456453

457454
/*
458-
* Order the keys inthe qualificationandbe sure that the scan
459-
*exploits the tree order.
455+
* Order thescankeys inour canonical fashionandeliminate any
456+
*redundant keys.
460457
*/
461-
so->numberOfFirstKeys=0;/* may be changed by _bt_orderkeys */
462-
so->qual_ok=1;/* may be changed by _bt_orderkeys */
463-
scan->scanFromEnd= false;
464-
strategyCheck= false;
465-
if (so->numberOfKeys>0)
466-
{
467-
_bt_orderkeys(rel,so);
458+
_bt_orderkeys(rel,so);
468459

469-
if (so->qual_ok)
470-
strategyCheck= true;
471-
}
460+
/*
461+
* Quit now if _bt_orderkeys() discovered that the scan keys can
462+
* never be satisfied (eg, x == 1 AND x > 2).
463+
*/
464+
if (!so->qual_ok)
465+
return (RetrieveIndexResult)NULL;
466+
467+
/*
468+
* Examine the scan keys to discover where we need to start the scan.
469+
*/
470+
scan->scanFromEnd= false;
472471
strat_total=BTEqualStrategyNumber;
473-
if (strategyCheck)
472+
if (so->numberOfKeys>0)
474473
{
475-
AttrNumberattno;
476-
477474
nKeyIs= (int*)palloc(so->numberOfKeys*sizeof(int));
478475
for (i=0;i<so->numberOfKeys;i++)
479476
{
480-
attno=so->keyData[i].sk_attno;
481-
if (attno==keysCount)
477+
AttrNumberattno=so->keyData[i].sk_attno;
478+
479+
/* ignore keys for already-determined attrs */
480+
if (attno <=keysCount)
482481
continue;
482+
/* if we didn't find a boundary for the preceding attr, quit */
483483
if (attno>keysCount+1)
484484
break;
485485
strat=_bt_getstrat(rel,attno,
486486
so->keyData[i].sk_procedure);
487+
/*
488+
* Can we use this key as a starting boundary for this attr?
489+
*
490+
* We can use multiple keys if they look like, say, = >= =
491+
* but we have to stop after accepting a > or < boundary.
492+
*/
487493
if (strat==strat_total||
488494
strat==BTEqualStrategyNumber)
489495
{
490496
nKeyIs[keysCount++]=i;
491-
continue;
492497
}
493-
if (ScanDirectionIsBackward(dir)&&
494-
(strat==BTLessStrategyNumber||
495-
strat==BTLessEqualStrategyNumber))
498+
elseif (ScanDirectionIsBackward(dir)&&
499+
(strat==BTLessStrategyNumber||
500+
strat==BTLessEqualStrategyNumber))
496501
{
497502
nKeyIs[keysCount++]=i;
498503
strat_total=strat;
499504
if (strat==BTLessStrategyNumber)
500505
break;
501-
continue;
502506
}
503-
if (ScanDirectionIsForward(dir)&&
504-
(strat==BTGreaterStrategyNumber||
505-
strat==BTGreaterEqualStrategyNumber))
507+
elseif (ScanDirectionIsForward(dir)&&
508+
(strat==BTGreaterStrategyNumber||
509+
strat==BTGreaterEqualStrategyNumber))
506510
{
507511
nKeyIs[keysCount++]=i;
508512
strat_total=strat;
509513
if (strat==BTGreaterStrategyNumber)
510514
break;
511-
continue;
512515
}
513516
}
514-
if (!keysCount)
517+
if (keysCount==0)
515518
scan->scanFromEnd= true;
516519
}
517520
else
518521
scan->scanFromEnd= true;
519522

520-
if (so->qual_ok==0)
521-
return (RetrieveIndexResult)NULL;
522-
523523
/* if we just need to walk down one edge of the tree, do that */
524524
if (scan->scanFromEnd)
525525
{
@@ -529,16 +529,14 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
529529
}
530530

531531
/*
532-
* Okay, we want something more complicated. What we'll do is use the
533-
* first item in the scan key passed in (which has been correctly
534-
* ordered to take advantage of index ordering) to position ourselves
535-
* at the right place in the scan.
532+
* We want to start the scan somewhere within the index. Set up a
533+
* scankey we can use to search for the correct starting point.
536534
*/
537535
scankeys= (ScanKey)palloc(keysCount*sizeof(ScanKeyData));
538536
for (i=0;i<keysCount;i++)
539537
{
540538
j=nKeyIs[i];
541-
/* _bt_orderkeys disallows it, but it's place to add some codelatter */
539+
/* _bt_orderkeys disallows it, but it's place to add some codelater */
542540
if (so->keyData[j].sk_flags&SK_ISNULL)
543541
{
544542
pfree(nKeyIs);
@@ -578,6 +576,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
578576
blkno=BufferGetBlockNumber(buf);
579577
page=BufferGetPage(buf);
580578

579+
/* position to the precise item on the page */
581580
offnum=_bt_binsrch(rel,buf,keysCount,scankeys);
582581

583582
ItemPointerSet(current,blkno,offnum);
@@ -595,7 +594,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
595594
* call _bt_endpoint() to set up a scan starting at that index endpoint,
596595
* as appropriate for the desired scan type.
597596
*
598-
* it's yet other place to add some codelatter for is(not)null ...
597+
* it's yet other place to add some codelater for is(not)null ...
599598
*----------
600599
*/
601600

@@ -737,13 +736,12 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
737736
itup=&btitem->bti_itup;
738737

739738
/* is the first item actually acceptable? */
740-
if (_bt_checkkeys(scan,itup,&keysok))
739+
if (_bt_checkkeys(scan,itup,dir,&continuescan))
741740
{
742741
/* yes, return it */
743742
res=FormRetrieveIndexResult(current,&(itup->t_tid));
744743
}
745-
elseif (keysok >=so->numberOfFirstKeys||
746-
(keysok== ((Size)-1)&&ScanDirectionIsBackward(dir)))
744+
elseif (continuescan)
747745
{
748746
/* no, but there might be another one that is */
749747
res=_bt_next(scan,dir);
@@ -906,7 +904,7 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
906904
IndexTupleitup;
907905
BTScanOpaqueso;
908906
RetrieveIndexResultres;
909-
Sizekeysok;
907+
boolcontinuescan;
910908

911909
rel=scan->relation;
912910
current=&(scan->currentItemData);
@@ -1012,13 +1010,12 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
10121010
itup=&(btitem->bti_itup);
10131011

10141012
/* see if we picked a winner */
1015-
if (_bt_checkkeys(scan,itup,&keysok))
1013+
if (_bt_checkkeys(scan,itup,dir,&continuescan))
10161014
{
10171015
/* yes, return it */
10181016
res=FormRetrieveIndexResult(current,&(itup->t_tid));
10191017
}
1020-
elseif (keysok >=so->numberOfFirstKeys||
1021-
(keysok== ((Size)-1)&&ScanDirectionIsBackward(dir)))
1018+
elseif (continuescan)
10221019
{
10231020
/* no, but there might be another one that is */
10241021
res=_bt_next(scan,dir);

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