From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
---|---|
To: | joao(at)e3c(dot)com(dot)br, Pg Docs <pgsql-docs(at)lists(dot)postgresql(dot)org> |
Subject: | Re: 'CREATE OR REPLACE FUNCTION' behavior whenever a transaction is running |
Date: | 2022-04-20 20:52:38 |
Message-ID: | CAKFQuwaOE2jieS1CJ-mWRAopuEpu+f36te0YRh8+tVivqQw1ng@mail.gmail.com |
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On Wed, Apr 20, 2022 at 12:50 PM PG Doc comments form <
noreply(at)postgresql(dot)org> wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/14/sql-createfunction.html
> Description:
>
> The page does not mention what is the default behavior whenever a function
> is replaced while the same function is being used in another
> query/transaction.
>
> Does the query fail? Does the 'CREATE OR REPLACE' operation fail? Does the
> query finish before the function is replaced?
>
> As a side note, my interest in this came from our need to use 'C-Language
> Functions', aka binary functions, so it would be neat to also add what is
> the behavior on those as well, if there's any difference.
>
IIUC pg_proc is administered using MVCC behavior just like any other
table. What you experience will be subject to your isolation mode but in
no case will a single command's execution see different versions nor will
such execution prevent the "replace"ment of the function with a newer
version.
Absent guidance to the contrary I wouldn't expect C language functions to
behave any differently than any others. But that just pertains to the
"REPLACE" aspect. You need to read the notes about C language functions to
get the rest of the story (and you likely wouldn't need to "replace" a
C-langauge function entry because of this different loading/compiling
mechanism). Namely:
https://www.postgresql.org/docs/current/xfunc-c.html#XFUNC-C-DYNLOAD
In short, C-language functions, referenced simply by name and module, and
pre-compiled, do not have a mechanism to invalidate the cache like pl/pgsql
functions do. Other languages may involve yet other dynamics.
David J.
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