Re: Is it useful to record whether plans are generic or custom?

On Sat, May 16, 2020 at 6:01 PM legrand legrand <legrand_legrand(at)hotmail(dot)com>
wrote:

> > To track executed plan types, I think execution layer hooks
> > are appropriate.
> > These hooks, however, take QueryDesc as a param and it does
> > not include cached plan information.
>
> It seems that the same QueryDesc entry is reused when executing
> a generic plan.
> For exemple marking queryDesc->plannedstmt->queryId (outside
> pg_stat_statements) with a pseudo tag during ExecutorStart
> reappears in later executions with generic plans ...
>
> Is this QueryDesc reusable by a custom plan ? If not maybe a solution
> could be to add a flag in queryDesc->plannedstmt ?
>

Thanks for your proposal!

I first thought it was a good idea and tried to add a flag to QueryDesc,
but the comments on QueryDesc say it encapsulates everything that
the executor needs to execute a query.

Whether a plan is generic or custom is not what executor needs to
know for running queries, so now I hesitate to do so.

Instead, I'm now considering using a static hash for prepared queries
(static HTAB *prepared_queries).

BTW, I'd also appreciate other opinions about recording the number
of generic and custom plans on pg_stat_statemtents.

Regards,

--
Atsushi Torikoshi