| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | João Paulo Labegalini de Carvalho <jaopaulolc(at)gmail(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andres Freund <andres(at)anarazel(dot)de> |
| Subject: | Re: Query JITing with LLVM ORC |
| Date: | 2022-09-21 19:28:19 |
| Message-ID: | CA+hUKGKkGkyM2p2r70rvFdy5KCPfAWBgXu1xL_3gwKv4KGV-SQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Sep 22, 2022 at 4:17 AM João Paulo Labegalini de Carvalho
<jaopaulolc(at)gmail(dot)com> wrote:
> I am working on a project with LLVM ORC that led us to PostgreSQL as a target application. We were surprised by learning that PGSQL already uses LLVM ORC to JIT certain queries.
It JITs expressions but not whole queries. Query execution at the
tuple-flow level is still done using a C call stack the same shape as
the query plan, but it *could* be transformed to a different control
flow that could be run more efficiently and perhaps JITed. CCing
Andres who developed all this and had some ideas about that...
> I would love to know what motivated this feature and for what it is being currently used for,
https://www.postgresql.org/docs/current/jit-reason.html
> as it is not enabled by default.
It's enabled by default in v12 and higher (if you built with
--with-llvm, as packagers do), but not always used:
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