Re: Failure while inserting parent tuple to B-tree is not fun

On Mon, Jan 27, 2014 at 10:27 AM, Heikki Linnakangas
<hlinnakangas(at)vmware(dot)com> wrote:
>> I think I see some bugs in _bt_moveright(). If you examine
>> _bt_finish_split() in detail, you'll see that it doesn't just drop the
>> write buffer lock that the caller will have provided (per its
>> comments) - it also drops the buffer pin. It calls _bt_insert_parent()
>> last, which was previously only called last thing by _bt_insertonpg()
>> (some of the time), and _bt_insertonpg() is indeed documented to drop
>> both the lock and the pin. And if you look at _bt_moveright() again,
>> you'll see that there is a tacit assumption that the buffer pin isn't
>> dropped, or at least that "opaque" (the BTPageOpaque BT special page
>> area pointer) continues to point to the same page held in the same
>> buffer, even though the code doesn't set the "opaque' pointer again
>> and it may not point to a pinned buffer or even the appropriate
>> buffer. Ditto "page". So "opaque" may point to the wrong thing on
>> subsequent iterations - you don't do anything with the return value of
>> _bt_getbuf(), unlike all of the existing call sites. I believe you
>> should store its return value, and get the held page and the special
>> pointer on the page, and assign that to the "opaque" pointer before
>> the next iteration (an iteration in which you very probably really do
>> make progress not limited to completing a page split, the occurrence
>> of which the _bt_moveright() loop gets "stuck on"). You know, do what
>> is done in the non-split-handling case. It may not always be the same
>> buffer as before, obviously.
>
>
> Yep, fixed.

Can you explain what the fix was, please?

--
Peter Geoghegan