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nbtree: Simplify _bt_first parallel scan handling.

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This new structure relieves _bt_first from having separate calls to
_bt_start_array_keys for the serial case and parallel case.  This saves
code, and seems clearer.

Follow-up to work from commits 4e6e375b and b5ee4e52.

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
This commit is contained in:
Peter Geoghegan 2025-01-07 10:29:46 -05:00
parent 2f8b4007db
commit 428a99b589
1 changed files with 38 additions and 50 deletions
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88
src/backend/access/nbtree/nbtsearch.c
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@ -890,6 +890,8 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
ScanKeyData notnullkeys[INDEX_MAX_KEYS];
int keysz = 0;
StrategyNumber strat_total;
BlockNumber blkno = InvalidBlockNumber,
lastcurrblkno;
Assert(!BTScanPosIsValid(so->currPos));
@ -905,64 +907,42 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
*/
if (!so->qual_ok)
{
Assert(!so->needPrimScan);
_bt_parallel_done(scan);
return false;
}
/*
* For parallel scans, get the starting page from shared state. If the
* scan has not started, proceed to find out first leaf page in the usual
* way while keeping other participating processes waiting. If the scan
* has already begun, use the page number from the shared structure.
*
* When a parallel scan has another primitive index scan scheduled, a
* parallel worker will seize the scan for that purpose now. This is
* similar to the case where the top-level scan hasn't started.
* If this is a parallel scan, we must seize the scan. _bt_readfirstpage
* will likely release the parallel scan later on.
*/
if (scan->parallel_scan != NULL)
{
BlockNumber blkno,
lastcurrblkno;
if (scan->parallel_scan != NULL &&
!_bt_parallel_seize(scan, &blkno, &lastcurrblkno, true))
return false;
if (!_bt_parallel_seize(scan, &blkno, &lastcurrblkno, true))
/*
* Initialize the scan's arrays (if any) for the current scan direction
* (except when they were already set to later values as part of
* scheduling the primitive index scan that is now underway)
*/
if (so->numArrayKeys && !so->needPrimScan)
_bt_start_array_keys(scan, dir);
if (blkno != InvalidBlockNumber)
{
/*
* We anticipated calling _bt_search, but another worker bet us to it.
* _bt_readnextpage releases the scan for us (not _bt_readfirstpage).
*/
Assert(scan->parallel_scan != NULL);
Assert(!so->needPrimScan);
Assert(blkno != P_NONE);
if (!_bt_readnextpage(scan, blkno, lastcurrblkno, dir, true))
return false;
/*
* Successfully seized the scan, which _bt_readfirstpage or possibly
* _bt_readnextpage will release (unless the scan ends right away, in
* which case we'll call _bt_parallel_done directly).
*
* Initialize arrays (when _bt_parallel_seize didn't already set up
* the next primitive index scan).
*/
if (so->numArrayKeys && !so->needPrimScan)
_bt_start_array_keys(scan, dir);
Assert(blkno != P_NONE);
if (blkno != InvalidBlockNumber)
{
Assert(!so->needPrimScan);
/*
* We anticipated starting another primitive scan, but some other
* worker bet us to it
*/
if (!_bt_readnextpage(scan, blkno, lastcurrblkno, dir, true))
return false;
_bt_returnitem(scan, so);
return true;
}
}
else if (so->numArrayKeys && !so->needPrimScan)
{
/*
* First _bt_first call (for current btrescan) without parallelism.
*
* Initialize arrays, and the corresponding scan keys that were just
* output by _bt_preprocess_keys.
*/
_bt_start_array_keys(scan, dir);
_bt_returnitem(scan, so);
return true;
}
/*
@ -1090,7 +1070,12 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
break;
startKeys[keysz++] = chosen;
/* Quit if we have stored a > or < key */
/*
* We can only consider adding more boundary keys when the one
* that we just chose to add uses either the = or >= strategy
* (during backwards scans we can only do so when the key that
* we just added to startKeys[] uses the = or <= strategy)
*/
strat_total = chosen->sk_strategy;
if (strat_total == BTGreaterStrategyNumber ||
strat_total == BTLessStrategyNumber)
@ -1190,6 +1175,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
Assert(subkey->sk_flags & SK_ROW_MEMBER);
if (subkey->sk_flags & SK_ISNULL)
{
Assert(!so->needPrimScan);
_bt_parallel_done(scan);
return false;
}
@ -1408,6 +1394,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
if (!BufferIsValid(so->currPos.buf))
{
Assert(!so->needPrimScan);
_bt_parallel_done(scan);
return false;
}
@ -2553,6 +2540,7 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
OffsetNumber start;
Assert(!BTScanPosIsValid(so->currPos));
Assert(!so->needPrimScan);
/*
* Scan down to the leftmost or rightmost leaf page. This is a simplified