Re: [PATCH] Do not flush BufFile for regular temp files

Hi!

Thanks for response.

I do not know whether this is correct to throw error when we can not do it.
'temp_file_limit' is enforced for actually created files and not on BufFile, so
if we can create one without it's associated file, then I see here no problems.

And this must be true for both normal and inter-xact, because in that case
owner backend is the only who can work with the file, so there is no need
to forcibly create disk file.

> Hello
>
> I think there is an issue with this patch: you are not taking into account a inter-transaction BufFile.
>
> If a BufFile is created with isInterXact set to true, BufFileClose does not flush data and this looks wrong.
>
> You can test this with the following extension https://github.com/pierreforstmann/buffile .
>
> With PostgreSQL 20devdel, I get:
> --
> -- Test BufFileClose() flushing behavior.
> --
> CREATE EXTENSION buffile;
> -- A regular temporary BufFile should not be flushed by BufFileClose().
> --
> -- With temp_file_limit = 0, a physical write must fail. Therefore
> -- false means that BufFileClose() did not attempt the write.
> SET temp_file_limit = 0;
> SELECT test_buffile_temp(false);
> INFO: BufFileClose has not flushed data
> test_buffile_temp
> -------------------
> f
> (1 row)
>
> -- An inter-transaction BufFile must still be flushed by BufFileClose().
> --
> -- Therefore the physical write should fail with temp_file_limit = 0.
> SELECT test_buffile_temp(true);
> INFO: BufFileClose has not flushed data
> test_buffile_temp
> -------------------
> f
> (1 row)
>
> RESET temp_file_limit;
> -- A FileSet BufFile must also be flushed by BufFileClose(), because
> -- another opener must be able to see its contents.
> SELECT test_buffile_fileset();
> INFO: BufFileClose has flushed data
> test_buffile_fileset
> ----------------------
> t
> (1 row)
>
>
> Regards
> Pierre Forstmann

---
Sergey Soloviev

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