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Commit8ca6d49

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Add helper functions to simplify heapgettup code
Here we add heapgettup_start_page() and heapgettup_continue_page() tosimplify the code in the heapgettup() function.Author: Melanie PlagemanReviewed-by: David RowleyDiscussion:https://postgr.es/m/CAAKRu_bvkhka0CZQun28KTqhuUh5ZqY=_T8QEqZqOL02rpi2bw@mail.gmail.com
1 parentf9bc34f commit8ca6d49

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+83
-35
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1 file changed

+83
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‎src/backend/access/heap/heapam.c

Lines changed: 83 additions & 35 deletions
Original file line numberDiff line numberDiff line change
@@ -544,6 +544,82 @@ heapgettup_initial_block(HeapScanDesc scan, ScanDirection dir)
544544
}
545545
}
546546

547+
548+
/*
549+
* heapgettup_start_page - helper function for heapgettup()
550+
*
551+
* Return the next page to scan based on the scan->rs_cbuf and set *linesleft
552+
* to the number of tuples on this page. Also set *lineoff to the first
553+
* offset to scan with forward scans getting the first offset and backward
554+
* getting the final offset on the page.
555+
*/
556+
staticPage
557+
heapgettup_start_page(HeapScanDescscan,ScanDirectiondir,int*linesleft,
558+
OffsetNumber*lineoff)
559+
{
560+
Pagepage;
561+
562+
Assert(scan->rs_inited);
563+
Assert(BufferIsValid(scan->rs_cbuf));
564+
565+
/* Caller is responsible for ensuring buffer is locked if needed */
566+
page=BufferGetPage(scan->rs_cbuf);
567+
568+
TestForOldSnapshot(scan->rs_base.rs_snapshot,scan->rs_base.rs_rd,page);
569+
570+
*linesleft=PageGetMaxOffsetNumber((Page)page)-FirstOffsetNumber+1;
571+
572+
if (ScanDirectionIsForward(dir))
573+
*lineoff=FirstOffsetNumber;
574+
else
575+
*lineoff= (OffsetNumber) (*linesleft);
576+
577+
/* lineoff now references the physically previous or next tid */
578+
returnpage;
579+
}
580+
581+
582+
/*
583+
* heapgettup_continue_page - helper function for heapgettup()
584+
*
585+
* Return the next page to scan based on the scan->rs_cbuf and set *linesleft
586+
* to the number of tuples left to scan on this page. Also set *lineoff to
587+
* the next offset to scan according to the ScanDirection in 'dir'.
588+
*/
589+
staticinlinePage
590+
heapgettup_continue_page(HeapScanDescscan,ScanDirectiondir,int*linesleft,
591+
OffsetNumber*lineoff)
592+
{
593+
Pagepage;
594+
595+
Assert(scan->rs_inited);
596+
Assert(BufferIsValid(scan->rs_cbuf));
597+
598+
/* Caller is responsible for ensuring buffer is locked if needed */
599+
page=BufferGetPage(scan->rs_cbuf);
600+
601+
TestForOldSnapshot(scan->rs_base.rs_snapshot,scan->rs_base.rs_rd,page);
602+
603+
if (ScanDirectionIsForward(dir))
604+
{
605+
*lineoff=OffsetNumberNext(scan->rs_coffset);
606+
*linesleft=PageGetMaxOffsetNumber(page)- (*lineoff)+1;
607+
}
608+
else
609+
{
610+
/*
611+
* The previous returned tuple may have been vacuumed since the
612+
* previous scan when we use a non-MVCC snapshot, so we must
613+
* re-establish the lineoff <= PageGetMaxOffsetNumber(page) invariant
614+
*/
615+
*lineoff=Min(PageGetMaxOffsetNumber(page),OffsetNumberPrev(scan->rs_coffset));
616+
*linesleft=*lineoff;
617+
}
618+
619+
/* lineoff now references the physically previous or next tid */
620+
returnpage;
621+
}
622+
547623
/* ----------------
548624
*heapgettup - fetch next heap tuple
549625
*
@@ -571,7 +647,6 @@ heapgettup(HeapScanDesc scan,
571647
ScanKeykey)
572648
{
573649
HeapTupletuple=&(scan->rs_ctup);
574-
Snapshotsnapshot=scan->rs_base.rs_snapshot;
575650
boolbackward=ScanDirectionIsBackward(dir);
576651
BlockNumberblock;
577652
boolfinished;
@@ -595,48 +670,20 @@ heapgettup(HeapScanDesc scan,
595670
tuple->t_data=NULL;
596671
return;
597672
}
673+
scan->rs_inited= true;
598674

599675
heapgetpage((TableScanDesc)scan,block);
600676

601677
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
602-
page=BufferGetPage(scan->rs_cbuf);
603-
TestForOldSnapshot(snapshot,scan->rs_base.rs_rd,page);
604-
605-
linesleft=PageGetMaxOffsetNumber(page)-FirstOffsetNumber+1;
606-
607-
if (ScanDirectionIsForward(dir))
608-
lineoff=FirstOffsetNumber;/* first offnum */
609-
else
610-
lineoff= (OffsetNumber)linesleft;
611-
612-
scan->rs_inited= true;
678+
page=heapgettup_start_page(scan,dir,&linesleft,&lineoff);
613679
}
614680
else
615681
{
616682
/* continue from previously returned page/tuple */
617683
block=scan->rs_cblock;
618684

619685
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
620-
page=BufferGetPage(scan->rs_cbuf);
621-
TestForOldSnapshot(snapshot,scan->rs_base.rs_rd,page);
622-
623-
if (ScanDirectionIsForward(dir))
624-
{
625-
lineoff=OffsetNumberNext(scan->rs_coffset);
626-
linesleft=PageGetMaxOffsetNumber(page)-lineoff+1;
627-
}
628-
else
629-
{
630-
/*
631-
* The previous returned tuple may have been vacuumed since the
632-
* previous scan when we use a non-MVCC snapshot, so we must
633-
* re-establish the lineoff <= PageGetMaxOffsetNumber(page)
634-
* invariant
635-
*/
636-
lineoff=Min(PageGetMaxOffsetNumber(page),
637-
OffsetNumberPrev(scan->rs_coffset));
638-
linesleft=lineoff;
639-
}
686+
page=heapgettup_continue_page(scan,dir,&linesleft,&lineoff);
640687
}
641688

642689
/*
@@ -667,12 +714,12 @@ heapgettup(HeapScanDesc scan,
667714
* if current tuple qualifies, return it.
668715
*/
669716
valid=HeapTupleSatisfiesVisibility(tuple,
670-
snapshot,
717+
scan->rs_base.rs_snapshot,
671718
scan->rs_cbuf);
672719

673720
HeapCheckForSerializableConflictOut(valid,scan->rs_base.rs_rd,
674721
tuple,scan->rs_cbuf,
675-
snapshot);
722+
scan->rs_base.rs_snapshot);
676723

677724
if (valid&&key!=NULL)
678725
valid=HeapKeyTest(tuple,RelationGetDescr(scan->rs_base.rs_rd),
@@ -773,7 +820,8 @@ heapgettup(HeapScanDesc scan,
773820
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
774821

775822
page=BufferGetPage(scan->rs_cbuf);
776-
TestForOldSnapshot(snapshot,scan->rs_base.rs_rd,page);
823+
TestForOldSnapshot(scan->rs_base.rs_snapshot,scan->rs_base.rs_rd,
824+
page);
777825
linesleft=PageGetMaxOffsetNumber(page);
778826
if (backward)
779827
{

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