On 22/04/2026 18:51, Masahiko Sawada wrote:
> On Fri, Apr 17, 2026 at 2:26 PM Andrei Lepikhov <lepihov@gmail.com> wrote:
>>
>> On 16/04/2026 19:58, Masahiko Sawada wrote:
> Understood. After more thoughts, I think your idea would be better.
>
> One thing still unclear to me is in which situation the query inthe
> test produces an array of unsorted offset numbers. While I understand
> it's not guaranteed that the DISTINCT clause returns the sorted
> result, doing DISTINCT in an aggregation function is using sort-based
> deduplication. I'd like to confirm that the queries in the test could
> end up producing the results that violate the assertion. Is it
> possible to do that by changing GUC parameters or something?
No, this is part of ongoing research into Postgres Optimizer vulnerabilities. I
used two tools: pg_pathcheck [1] and pg-chaos-mode [2]. The first tool finds
hidden dangling pointers in pathlists, which we are currently discussing in
another thread. The second is a patch that makes the cost-based decision random
to help uncover hidden or unwritten coding contracts.
Both tools are experimental and not meant for core use; they are only used to
trigger potential issues. In this case, I think the query picked a costly sorted
path, which led to the crash.
[1] https://github.com/danolivo/pg_pathcheck
[2] https://github.com/danolivo/pg-chaos-test
--
regards, Andrei Lepikhov,
pgEdge
