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Fix obsolete _bt_first comments.

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_bt_first doesn't necessarily hold onto a buffer pin on success exit.
Fix header comments that claimed that we'll always hold onto a pin.

Oversight in commit 2ed5b87f96.
This commit is contained in:
Peter Geoghegan 2024-11-04 12:43:54 -05:00
parent 0d82970336
commit 846cfe0dcc
1 changed files with 7 additions and 4 deletions
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11
src/backend/access/nbtree/nbtsearch.c
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@ -862,14 +862,15 @@ _bt_compare(Relation rel,
* We need to be clever about the direction of scan, the search * We need to be clever about the direction of scan, the search
* conditions, and the tree ordering. We find the first item (or, * conditions, and the tree ordering. We find the first item (or,
* if backwards scan, the last item) in the tree that satisfies the * if backwards scan, the last item) in the tree that satisfies the
* qualifications in the scan key. On success exit, the page containing * qualifications in the scan key. On success exit, data about the
* the current index tuple is pinned but not locked, and data about * matching tuple(s) on the page has been loaded into so->currPos. We'll
* the matching tuple(s) on the page has been loaded into so->currPos. * drop all locks and hold onto a pin on page's buffer, except when
* _bt_drop_lock_and_maybe_pin dropped the pin to avoid blocking VACUUM.
* scan->xs_heaptid is set to the heap TID of the current tuple, and if * scan->xs_heaptid is set to the heap TID of the current tuple, and if
* requested, scan->xs_itup points to a copy of the index tuple. * requested, scan->xs_itup points to a copy of the index tuple.
* *
* If there are no matching items in the index, we return false, with no * If there are no matching items in the index, we return false, with no
* pins or locks held. * pins or locks held. so->currPos will remain invalid.
* *
* Note that scan->keyData[], and the so->keyData[] scankey built from it, * Note that scan->keyData[], and the so->keyData[] scankey built from it,
* are both search-type scankeys (see nbtree/README for more about this). * are both search-type scankeys (see nbtree/README for more about this).
@ -1470,6 +1471,8 @@ _bt_next(IndexScanDesc scan, ScanDirection dir)
BTScanOpaque so = (BTScanOpaque) scan->opaque; BTScanOpaque so = (BTScanOpaque) scan->opaque;
BTScanPosItem *currItem; BTScanPosItem *currItem;
Assert(BTScanPosIsValid(so->currPos));
/* /*
* Advance to next tuple on current page; or if there's no more, try to * Advance to next tuple on current page; or if there's no more, try to
* step to the next page with data. * step to the next page with data.