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

Andres Freund <andres@anarazel.de>

From: Andres Freund <andres@anarazel.de>

To: Andreas Joseph Krogh <andreas@visena.com>

Cc: pgsql-hackers@lists.postgresql.org

Date: 2018-04-18T15:50:55Z

Lists: pgsql-hackers

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

Commits

Fix issues around EXPLAIN with JIT.
- e97c4d967ba5 11.0 landed
- c03c1449c092 12.0 landed
Collect JIT instrumentation from workers.
- e63441c3f5ca 11.0 landed
- 33001fd7a707 12.0 landed
Make EXPLAIN output for JIT compilation more dense.
- 6859bd2632d8 11.0 landed
- 52050ad8ebec 12.0 landed
Save/restore SPI's global variables in SPI_connect() and SPI_finish().
- 825f10fbda7a 11.0 cited
Rationalize handling of single and double quotes in bootstrap data.
- 55d26ff638f0 11.0 cited