Re: postgres chooses objectively wrong index

On 2026-03-18 03:01, Merlin Moncure wrote:
> I've been maintaining an airflow style orchestrator in pl/pgsql, and 
> it's revealed a performance issue I just can't solve.  There is a 
> table, task, which may normally contain billions of rows, but only a 
> tiny portion is interesting for specific reasons—a common pattern in 
> task-type systems.
>
> ...
>
> I'm wondering if there are other tricks that might apply here, for 
> example, multi column index statistics...curious if anyone has 
> thoughts on that.
>
> Any suggestions?
>
> merlin
>
Hello. I think planner doesn't have information about distribution of 
*async.task_execution_state(task)* unless it's part of any full index. I 
would try to give that with extended statistics (postgresql 14+):

create statistics (mcv) task_task_execution_state_stat on ((async.task_execution_state(task))) from async.task;
analyze async.task;

If that won't help - please show distribution from pg_stats_ext view for 
extended statistic above.


--
Alexey Ermakov