From bbe35ac54d5b0de5ebc61131c5deb91fc026f4de Mon Sep 17 00:00:00 2001 From: Yugo Nagata Date: Tue, 24 Mar 2026 18:23:14 +0900 Subject: [PATCH v2 1/2] Clarify _bt_binsrch comments for internal vs leaf page usage --- src/backend/access/nbtree/nbtsearch.c | 28 ++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-) diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c index aae6acb7f57..5ebb6a061d0 100644 --- a/src/backend/access/nbtree/nbtsearch.c +++ b/src/backend/access/nbtree/nbtsearch.c @@ -324,17 +324,19 @@ _bt_moveright(Relation rel, /* * _bt_binsrch() -- Do a binary search for a key on a particular page. * - * On an internal (non-leaf) page, _bt_binsrch() returns the OffsetNumber - * of the last key < given scankey, or last key <= given scankey if nextkey - * is true. (Since _bt_compare treats the first data key of such a page as - * minus infinity, there will be at least one key < scankey, so the result - * always points at one of the keys on the page.) + * When called from _bt_search() to find a downlink on an internal (non-leaf) + * page, _bt_binsrch() returns the OffsetNumber of the last key < given scankey, + * or last key <= given scankey if nextkey is true. (Since _bt_compare treats + * the first data key of such a page as minus infinity, there will be at least + * one key < scankey, so the result always points at one of the keys on the + * page.) * - * On a leaf page, _bt_binsrch() returns the final result of the initial - * positioning process that started with _bt_first's call to _bt_search. - * We're returning a non-pivot tuple offset, so things are a little different. - * It is possible that we'll return an offset that's either past the last - * non-pivot slot, or (in the case of a backward scan) before the first slot. + * When called from _bt_first() to find a key on a leaf page, _bt_binsrch() + * returns the final result of the initial positioning process that started + * with _bt_search. Since we're returning a non-pivot tuple offset, the logic + * differs slightly. It is possible that we'll return an offset that's either + * past the last non-pivot slot, or (in the case of a backward scan) before the + * first slot. * * This procedure is not responsible for walking right, it just examines * the given page. _bt_binsrch() has no lock or refcount side effects @@ -1538,12 +1540,12 @@ _bt_first(IndexScanDesc scan, ScanDirection dir) } } - /* position to the precise item on the page */ + /* position to the precise item on the leaf page */ offnum = _bt_binsrch(rel, &inskey, so->currPos.buf); /* - * Now load data from the first page of the scan (usually the page - * currently in so->currPos.buf). + * Now load data from the first leaf page of the scan (usually the + * page currently in so->currPos.buf). * * If inskey.nextkey = false and inskey.backward = false, offnum is * positioned at the first non-pivot tuple >= inskey.scankeys. -- 2.43.0