Re: BUG #17871: JIT during postgresql_fdw remote_estimates EXPLAIN have very negatively effect on planning time

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: Andres Freund <andres@anarazel.de>, maxim.boguk@gmail.com, pgsql-bugs@lists.postgresql.org

Date: 2023-03-28T03:05:00Z

Lists: pgsql-bugs

Attachments

dont_jit_with_explain_only.patch (application/octet-stream) patch

On Tue, 28 Mar 2023 at 10:38, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I was wondering if we could skip doing even that much when
> EXEC_FLAG_EXPLAIN_ONLY is set.  Without a test case, though,
> I'm not very sure where the jitter is getting reached.

It seems to be coming from the qual initialisation in nodeSeqscan.c:
ie. ExecInitSeqScan -> ExecInitQual -> ExecReadyExpr ->
jit_compile_expr

I guess that means just add a check for EXEC_FLAG_EXPLAIN_ONLY in
jit_compile_expr, or only set the es_jit_flags bits in
standard_ExecutorStart() when not in EXEC_FLAG_EXPLAIN_ONLY. I'm not
really sure which of those is better, but the attached does the former
and seems to fix the issue.

David