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Commit428a99b

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nbtree: Simplify _bt_first parallel scan handling.
This new structure relieves _bt_first from having separate calls to_bt_start_array_keys for the serial case and parallel case. This savescode, and seems clearer.Follow-up to work from commits4e6e375 andb5ee4e5.Author: Peter Geoghegan <pg@bowt.ie>Reviewed-By: Matthias van de Meent <boekewurm+postgres@gmail.com>Discussion:https://postgr.es/m/CAH2-Wz=XjUZjBjHJdhTvuH5MwoJObWGoM2RG2LyFg5WUdWyk=A@mail.gmail.com
1 parent2f8b400 commit428a99b

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+34
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1 file changed

+34
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‎src/backend/access/nbtree/nbtsearch.c‎

Lines changed: 34 additions & 46 deletions
Original file line numberDiff line numberDiff line change
@@ -890,6 +890,8 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
890890
ScanKeyDatanotnullkeys[INDEX_MAX_KEYS];
891891
intkeysz=0;
892892
StrategyNumberstrat_total;
893+
BlockNumberblkno=InvalidBlockNumber,
894+
lastcurrblkno;
893895

894896
Assert(!BTScanPosIsValid(so->currPos));
895897

@@ -905,64 +907,42 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
905907
*/
906908
if (!so->qual_ok)
907909
{
910+
Assert(!so->needPrimScan);
908911
_bt_parallel_done(scan);
909912
return false;
910913
}
911914

912915
/*
913-
* For parallel scans, get the starting page from shared state. If the
914-
* scan has not started, proceed to find out first leaf page in the usual
915-
* way while keeping other participating processes waiting. If the scan
916-
* has already begun, use the page number from the shared structure.
917-
*
918-
* When a parallel scan has another primitive index scan scheduled, a
919-
* parallel worker will seize the scan for that purpose now. This is
920-
* similar to the case where the top-level scan hasn't started.
916+
* If this is a parallel scan, we must seize the scan. _bt_readfirstpage
917+
* will likely release the parallel scan later on.
921918
*/
922-
if (scan->parallel_scan!=NULL)
923-
{
924-
BlockNumberblkno,
925-
lastcurrblkno;
919+
if (scan->parallel_scan!=NULL&&
920+
!_bt_parallel_seize(scan,&blkno,&lastcurrblkno, true))
921+
return false;
926922

927-
if (!_bt_parallel_seize(scan,&blkno,&lastcurrblkno, true))
928-
return false;
923+
/*
924+
* Initialize the scan's arrays (if any) for the current scan direction
925+
* (except when they were already set to later values as part of
926+
* scheduling the primitive index scan that is now underway)
927+
*/
928+
if (so->numArrayKeys&& !so->needPrimScan)
929+
_bt_start_array_keys(scan,dir);
929930

931+
if (blkno!=InvalidBlockNumber)
932+
{
930933
/*
931-
* Successfully seized the scan, which _bt_readfirstpage or possibly
932-
* _bt_readnextpage will release (unless the scan ends right away, in
933-
* which case we'll call _bt_parallel_done directly).
934-
*
935-
* Initialize arrays (when _bt_parallel_seize didn't already set up
936-
* the next primitive index scan).
934+
* We anticipated calling _bt_search, but another worker bet us to it.
935+
* _bt_readnextpage releases the scan for us (not _bt_readfirstpage).
937936
*/
938-
if (so->numArrayKeys&& !so->needPrimScan)
939-
_bt_start_array_keys(scan,dir);
940-
937+
Assert(scan->parallel_scan!=NULL);
938+
Assert(!so->needPrimScan);
941939
Assert(blkno!=P_NONE);
942-
if (blkno!=InvalidBlockNumber)
943-
{
944-
Assert(!so->needPrimScan);
945940

946-
/*
947-
* We anticipated starting another primitive scan, but some other
948-
* worker bet us to it
949-
*/
950-
if (!_bt_readnextpage(scan,blkno,lastcurrblkno,dir, true))
951-
return false;
941+
if (!_bt_readnextpage(scan,blkno,lastcurrblkno,dir, true))
942+
return false;
952943

953-
_bt_returnitem(scan,so);
954-
return true;
955-
}
956-
}
957-
elseif (so->numArrayKeys&& !so->needPrimScan)
958-
{
959-
/*
960-
* First _bt_first call (for current btrescan) without parallelism.
961-
*
962-
* Initialize arrays, and the corresponding scan keys that were just
963-
* output by _bt_preprocess_keys.
964-
*/
965-
_bt_start_array_keys(scan,dir);
944+
_bt_returnitem(scan,so);
945+
return true;
966946
}
967947

968948
/*
@@ -1090,7 +1070,12 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
10901070
break;
10911071
startKeys[keysz++]=chosen;
10921072

1093-
/* Quit if we have stored a > or < key */
1073+
/*
1074+
* We can only consider adding more boundary keys when the one
1075+
* that we just chose to add uses either the = or >= strategy
1076+
* (during backwards scans we can only do so when the key that
1077+
* we just added to startKeys[] uses the = or <= strategy)
1078+
*/
10941079
strat_total=chosen->sk_strategy;
10951080
if (strat_total==BTGreaterStrategyNumber||
10961081
strat_total==BTLessStrategyNumber)
@@ -1190,6 +1175,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
11901175
Assert(subkey->sk_flags&SK_ROW_MEMBER);
11911176
if (subkey->sk_flags&SK_ISNULL)
11921177
{
1178+
Assert(!so->needPrimScan);
11931179
_bt_parallel_done(scan);
11941180
return false;
11951181
}
@@ -1408,6 +1394,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
14081394

14091395
if (!BufferIsValid(so->currPos.buf))
14101396
{
1397+
Assert(!so->needPrimScan);
14111398
_bt_parallel_done(scan);
14121399
return false;
14131400
}
@@ -2553,6 +2540,7 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
25532540
OffsetNumberstart;
25542541

25552542
Assert(!BTScanPosIsValid(so->currPos));
2543+
Assert(!so->needPrimScan);
25562544

25572545
/*
25582546
* Scan down to the leftmost or rightmost leaf page. This is a simplified

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