Re: postgresql13-llvm jit-13.5-1PGDG.rhel8.x86_64

Hi

> There is a CentOS8-stream version which solves the problem but I cannot
> use that in the office. I will probably have to wait for another month
> before OL8 has everything that I need in its repositories. Now, the
> question is what kind of an impact will running without llvm-jit have?
> According to the links below, llvm-jit effects are quite spectacular:
>
> https://llvm.org/devmtg/2016-09/slides/Melnik-PostgreSQLLLVM.pdf
>
> https://www.pgcon.org/2017/schedule/events/1092.en.html

When JIT was used on very large query with a lot of CASE expr, then JIT has
a positive effect about 50%. On usual large queries, the effect of JIT was
about 20%. Unfortunately, JIT is sensitive to estimation, and the JIT
sometimes increases seconds to queries, although without JIT this query is
executed in ms. When you use a query that can be well calculated in
parallel, then positive effect of JIT is less.

Regards

Pavel

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> Mladen Gogala
> Database Consultant
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> https://dbwhisperer.wordpress.com
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