| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | David Rowley <dgrowleyml(at)gmail(dot)com>, Scott Ribe <scott_ribe(at)elevated-dev(dot)com>, PostgreSQL General <pgsql-general(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: bad JIT decision |
| Date: | 2020-07-25 00:16:05 |
| Message-ID: | 20200725001605.vrlncip4fx3esv3b@alap3.anarazel.de |
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| Thread: | |
| Lists: | pgsql-general |
Hi,
On 2020-07-24 18:37:02 -0400, Tom Lane wrote:
> David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> > However, for now, you might just want to try raising various jit
> > thresholds so that it only is enabled for more expensive plans.
>
> Yeah. I'm fairly convinced that the v12 defaults are far too low,
> because we are constantly seeing complaints of this sort.
I think the issue is more that we need to take into accoutn that the
overhead of JITing scales ~linearly with the number of JITed
expressions. And that's not done right now. I've had a patch somewhere
that had a prototype implementation of changing the costing to be
#expressions * some_cost, and I think that's a lot more accurate.
Greetings,
Andres Freund
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