Re: Failure in contrib test _int on loach

On 10/04/2019 20:25, Heikki Linnakangas wrote:
> On 09/04/2019 19:11, Anastasia Lubennikova wrote:
>> 05.04.2019 19:41, Anastasia Lubennikova writes:
>>> In attachment, you can find patch with a test that allows to reproduce
>>> the bug not randomly, but on every run.
>>> Now I'm trying to find a way to fix the issue.
>>
>> The problem was caused by incorrect detection of the page to insert new
>> tuple after split.
>> If gistinserttuple() of the tuple formed by gistgetadjusted() had to
>> split the page, we must to go back to the parent and
>> descend back to the child that's a better fit for the new tuple.
>>
>> Previously this was handled by the code block with the following comment:
>>
>> * Concurrent split detected. There's no guarantee that the
>> * downlink for this page is consistent with the tuple we're
>> * inserting anymore, so go back to parent and rechoose the best
>> * child.
>>
>> After introducing GistBuildNSN this code path became unreachable.
>> To fix it, I added new flag to detect such splits during indexbuild.
> 
> Isn't it possible that the grandparent page is also split, so that we'd 
> need to climb further up?
Based on Anastasia's idea i prepare alternative solution to fix the bug 
(see attachment).
It utilizes the idea of linear increment of LSN/NSN. WAL write process 
is used for change NSN value to 1 for each block of index relation.
I hope this can be a fairly clear and safe solution.

-- 
Andrey Lepikhov
Postgres Professional
https://postgrespro.com
The Russian Postgres Company