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Re: bad JIT decision

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Hi,

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