Re: Query is over 2x slower with jit=on

From: Andres Freund <andres(at)anarazel(dot)de>
To: Andreas Joseph Krogh <andreas(at)visena(dot)com>
Cc: pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: Query is over 2x slower with jit=on
Date: 2018-04-18 15:50:55
Message-ID: 20180418155055.gawfkerzvy5rxpxe@alap3.anarazel.de
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On 2018-04-18 17:35:31 +0200, Andreas Joseph Krogh wrote:
> With jit=on:
> https://explain.depesz.com/s/vYB
> Planning Time: 0.336 ms
> JIT:
>  Functions: 716
>  Generation Time: 78.404 ms
>  Inlining: false
>  Inlining Time: 0.000 ms
>  Optimization: false
>  Optimization Time: 43.916 ms
>  Emission Time: 600.031 ms

Any chance this is a debug LLVM build?

> What's the deal with jit making it slower?

JIT has cost, and sometimes it's not beneficial. Here our heuristics
when to JIT appear to be a bit off. In the parallel world it's worse
because the JITing is duplicated for parallel workers atm.

Greetings,

Andres Freund

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