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Commitf9bc34f

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Further refactor of heapgettup and heapgettup_pagemode
Backward and forward scans share much of the same page acquisition code.Here we consolidate that code to reduce some duplication.Additionally, add a new rs_coffset field to HeapScanDescData to track theoffset of the current tuple. The new field fits nicely into the paddingbetween a bool and BlockNumber field and saves having to look at the lastreturned tuple to figure out which offset we should be looking at for thecurrent tuple.Author: Melanie PlagemanReviewed-by: David RowleyDiscussion:https://postgr.es/m/CAAKRu_bvkhka0CZQun28KTqhuUh5ZqY=_T8QEqZqOL02rpi2bw@mail.gmail.com
1 parentcdf6518 commitf9bc34f

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2 files changed

+63
-138
lines changed

2 files changed

+63
-138
lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 62 additions & 138 deletions
Original file line numberDiff line numberDiff line change
@@ -576,101 +576,67 @@ heapgettup(HeapScanDesc scan,
576576
BlockNumberblock;
577577
boolfinished;
578578
Pagepage;
579-
intlines;
580579
OffsetNumberlineoff;
581580
intlinesleft;
582581
ItemIdlpp;
583582

584-
/*
585-
* calculate next starting lineoff, given scan direction
586-
*/
587-
if (ScanDirectionIsForward(dir))
583+
if (unlikely(!scan->rs_inited))
588584
{
589-
if (!scan->rs_inited)
590-
{
591-
block=heapgettup_initial_block(scan,dir);
585+
block=heapgettup_initial_block(scan,dir);
592586

593-
/*
594-
* Check if we have reached the end of the scan already. This
595-
* could happen if the table is empty or if the parallel workers
596-
* have already finished the scan before we did anything ourselves
597-
*/
598-
if (block==InvalidBlockNumber)
599-
{
600-
Assert(!BufferIsValid(scan->rs_cbuf));
601-
tuple->t_data=NULL;
602-
return;
603-
}
604-
heapgetpage((TableScanDesc)scan,block);
605-
lineoff=FirstOffsetNumber;/* first offnum */
606-
scan->rs_inited= true;
607-
}
608-
else
587+
/*
588+
* Check if we have reached the end of the scan already. This could
589+
* happen if the table is empty or if the parallel workers have
590+
* already finished the scan before we did anything ourselves
591+
*/
592+
if (block==InvalidBlockNumber)
609593
{
610-
/* continue from previously returned page/tuple */
611-
block=scan->rs_cblock;/* current page */
612-
lineoff=/* next offnum */
613-
OffsetNumberNext(ItemPointerGetOffsetNumber(&(tuple->t_self)));
594+
Assert(!BufferIsValid(scan->rs_cbuf));
595+
tuple->t_data=NULL;
596+
return;
614597
}
615598

616-
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
599+
heapgetpage((TableScanDesc)scan,block);
617600

601+
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
618602
page=BufferGetPage(scan->rs_cbuf);
619603
TestForOldSnapshot(snapshot,scan->rs_base.rs_rd,page);
620-
lines=PageGetMaxOffsetNumber(page);
621-
/* block and lineoff now reference the physically next tid */
622604

623-
linesleft=lines-lineoff+1;
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;
624613
}
625614
else
626615
{
627-
if (!scan->rs_inited)
628-
{
629-
block=heapgettup_initial_block(scan,dir);
630-
631-
/*
632-
* Check if we have reached the end of the scan already. This
633-
* could happen if the table is empty.
634-
*/
635-
if (block==InvalidBlockNumber)
636-
{
637-
Assert(!BufferIsValid(scan->rs_cbuf));
638-
tuple->t_data=NULL;
639-
return;
640-
}
616+
/* continue from previously returned page/tuple */
617+
block=scan->rs_cblock;
641618

642-
heapgetpage((TableScanDesc)scan,block);
643-
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
619+
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
620+
page=BufferGetPage(scan->rs_cbuf);
621+
TestForOldSnapshot(snapshot,scan->rs_base.rs_rd,page);
644622

645-
page=BufferGetPage(scan->rs_cbuf);
646-
TestForOldSnapshot(snapshot,scan->rs_base.rs_rd,page);
647-
lines=PageGetMaxOffsetNumber(page);
648-
lineoff=lines;/* final offnum */
649-
scan->rs_inited= true;
623+
if (ScanDirectionIsForward(dir))
624+
{
625+
lineoff=OffsetNumberNext(scan->rs_coffset);
626+
linesleft=PageGetMaxOffsetNumber(page)-lineoff+1;
650627
}
651628
else
652629
{
653-
/* continue from previously returned page/tuple */
654-
block=scan->rs_cblock;/* current page */
655-
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
656-
657-
page=BufferGetPage(scan->rs_cbuf);
658-
TestForOldSnapshot(snapshot,scan->rs_base.rs_rd,page);
659-
lines=PageGetMaxOffsetNumber(page);
660-
661630
/*
662631
* The previous returned tuple may have been vacuumed since the
663632
* previous scan when we use a non-MVCC snapshot, so we must
664633
* re-establish the lineoff <= PageGetMaxOffsetNumber(page)
665634
* invariant
666635
*/
667-
lineoff=/* previous offnum */
668-
Min(lines,
669-
OffsetNumberPrev(ItemPointerGetOffsetNumber(&(tuple->t_self))));
636+
lineoff=Min(PageGetMaxOffsetNumber(page),
637+
OffsetNumberPrev(scan->rs_coffset));
638+
linesleft=lineoff;
670639
}
671-
/* block and lineoff now reference the physically previous tid */
672-
673-
linesleft=lineoff;
674640
}
675641

676642
/*
@@ -715,6 +681,7 @@ heapgettup(HeapScanDesc scan,
715681
if (valid)
716682
{
717683
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_UNLOCK);
684+
scan->rs_coffset=lineoff;
718685
return;
719686
}
720687
}
@@ -807,12 +774,11 @@ heapgettup(HeapScanDesc scan,
807774

808775
page=BufferGetPage(scan->rs_cbuf);
809776
TestForOldSnapshot(snapshot,scan->rs_base.rs_rd,page);
810-
lines=PageGetMaxOffsetNumber(page);
811-
linesleft=lines;
777+
linesleft=PageGetMaxOffsetNumber(page);
812778
if (backward)
813779
{
814-
lineoff=lines;
815-
lpp=PageGetItemId(page,lines);
780+
lineoff=linesleft;
781+
lpp=PageGetItemId(page,linesleft);
816782
}
817783
else
818784
{
@@ -846,87 +812,46 @@ heapgettup_pagemode(HeapScanDesc scan,
846812
BlockNumberblock;
847813
boolfinished;
848814
Pagepage;
849-
intlines;
850815
intlineindex;
851816
OffsetNumberlineoff;
852817
intlinesleft;
853818
ItemIdlpp;
854819

855-
/*
856-
* calculate next starting lineindex, given scan direction
857-
*/
858-
if (ScanDirectionIsForward(dir))
820+
if (unlikely(!scan->rs_inited))
859821
{
860-
if (!scan->rs_inited)
861-
{
862-
block=heapgettup_initial_block(scan,dir);
822+
block=heapgettup_initial_block(scan,dir);
863823

864-
/*
865-
* Check if we have reached the end of the scan already. This
866-
* could happen if the table is empty or if the parallel workers
867-
* have already finished the scan before we did anything ourselves
868-
*/
869-
if (block==InvalidBlockNumber)
870-
{
871-
Assert(!BufferIsValid(scan->rs_cbuf));
872-
tuple->t_data=NULL;
873-
return;
874-
}
875-
heapgetpage((TableScanDesc)scan,block);
876-
lineindex=0;
877-
scan->rs_inited= true;
878-
}
879-
else
824+
/*
825+
* Check if we have reached the end of the scan already. This could
826+
* happen if the table is empty or if the other workers in a parallel
827+
* scan have already finished the scan.
828+
*/
829+
if (block==InvalidBlockNumber)
880830
{
881-
/* continue from previously returned page/tuple */
882-
block=scan->rs_cblock;/* current page */
883-
lineindex=scan->rs_cindex+1;
831+
Assert(!BufferIsValid(scan->rs_cbuf));
832+
tuple->t_data=NULL;
833+
return;
884834
}
885835

836+
heapgetpage((TableScanDesc)scan,block);
886837
page=BufferGetPage(scan->rs_cbuf);
887838
TestForOldSnapshot(scan->rs_base.rs_snapshot,scan->rs_base.rs_rd,page);
888-
lines=scan->rs_ntuples;
889-
/* block and lineindex now reference the next visible tid */
890-
891-
linesleft=lines-lineindex;
839+
linesleft=scan->rs_ntuples;
840+
lineindex=ScanDirectionIsForward(dir) ?0 :linesleft-1;
841+
scan->rs_inited= true;
892842
}
893843
else
894844
{
895-
if (!scan->rs_inited)
896-
{
897-
block=heapgettup_initial_block(scan,dir);
898-
899-
/*
900-
* Check if we have reached the end of the scan already. This
901-
* could happen if the table is empty.
902-
*/
903-
if (block==InvalidBlockNumber)
904-
{
905-
Assert(!BufferIsValid(scan->rs_cbuf));
906-
tuple->t_data=NULL;
907-
return;
908-
}
845+
/* continue from previously returned page/tuple */
846+
block=scan->rs_cblock;/* current page */
847+
page=BufferGetPage(scan->rs_cbuf);
848+
TestForOldSnapshot(scan->rs_base.rs_snapshot,scan->rs_base.rs_rd,page);
909849

910-
heapgetpage((TableScanDesc)scan,block);
911-
page=BufferGetPage(scan->rs_cbuf);
912-
TestForOldSnapshot(scan->rs_base.rs_snapshot,scan->rs_base.rs_rd,page);
913-
lines=scan->rs_ntuples;
914-
lineindex=lines-1;
915-
scan->rs_inited= true;
916-
}
850+
lineindex=scan->rs_cindex+dir;
851+
if (ScanDirectionIsForward(dir))
852+
linesleft=scan->rs_ntuples-lineindex;
917853
else
918-
{
919-
/* continue from previously returned page/tuple */
920-
block=scan->rs_cblock;/* current page */
921-
922-
page=BufferGetPage(scan->rs_cbuf);
923-
TestForOldSnapshot(scan->rs_base.rs_snapshot,scan->rs_base.rs_rd,page);
924-
lines=scan->rs_ntuples;
925-
lineindex=scan->rs_cindex-1;
926-
}
927-
/* block and lineindex now reference the previous visible tid */
928-
929-
linesleft=lineindex+1;
854+
linesleft=scan->rs_cindex;
930855
}
931856

932857
/*
@@ -1041,10 +966,9 @@ heapgettup_pagemode(HeapScanDesc scan,
1041966

1042967
page=BufferGetPage(scan->rs_cbuf);
1043968
TestForOldSnapshot(scan->rs_base.rs_snapshot,scan->rs_base.rs_rd,page);
1044-
lines=scan->rs_ntuples;
1045-
linesleft=lines;
969+
linesleft=scan->rs_ntuples;
1046970
if (backward)
1047-
lineindex=lines-1;
971+
lineindex=linesleft-1;
1048972
else
1049973
lineindex=0;
1050974
}

‎src/include/access/heapam.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -57,6 +57,7 @@ typedef struct HeapScanDescData
5757

5858
/* scan current state */
5959
boolrs_inited;/* false = scan not init'd yet */
60+
OffsetNumberrs_coffset;/* current offset # in non-page-at-a-time mode */
6061
BlockNumberrs_cblock;/* current block # in scan, if any */
6162
Bufferrs_cbuf;/* current buffer in scan, if any */
6263
/* NB: if rs_cbuf is not InvalidBuffer, we hold a pin on that buffer */

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