Re: issue: nbtpage.c,_bt_pagedel may get wrong result

On 23/05/2024 13:06, Pengfei Wang wrote:
> # issue
> https://github.com/postgres/postgres/blob/da32f5c4bca7f3447b869de2afbbfa0b74443d45/src/backend/access/nbtree/nbtpage.c#L1943 <https://github.com/postgres/postgres/blob/da32f5c4bca7f3447b869de2afbbfa0b74443d45/src/backend/access/nbtree/nbtpage.c#L1943>
>
> /*
> * To avoid deadlocks, we'd better drop the leaf page lock
> * before going further.
> */
> _bt_unlockbuf(rel, leafbuf);
>
> /*
> * Check that the left sibling of leafbuf (if any) is not
> * marked with INCOMPLETE_SPLIT flag before proceeding
> */
> Assert(leafblkno == scanblkno);
> if (_bt_leftsib_splitflag(rel, leftsib, leafblkno))
> {
>     ReleaseBuffer(leafbuf);
>     return;
> }
>
> After unlocking leaf, but before call _bt_leftsib_splitflag, leftsib may
> be already split, and leafbuf's current left sibling is in
> INCOMPLETE_SPLIT status.

In that case, there should be a downlink for 'leafbuf' in the parent,
and we're good to proceed, right? See the comments in
_bt_leftsib_splitflag().

--
Heikki Linnakangas
Neon (https://neon.tech)