Re: bad JIT decision - Mailing list pgsql-general

From Andres Freund
Subject Re: bad JIT decision
Date
Msg-id 20200725001605.vrlncip4fx3esv3b@alap3.anarazel.de
Whole thread Raw
In response to Re: bad JIT decision  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: bad JIT decision
Re: bad JIT decision
List pgsql-general
Hi,

On 2020-07-24 18:37:02 -0400, Tom Lane wrote:
> David Rowley <dgrowleyml@gmail.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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