| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Dagfinn Ilmari Mannsåker <ilmari(at)ilmari(dot)org>, Christoph Berg <myon(at)debian(dot)org>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Direct I/O |
| Date: | 2023-04-14 18:56:32 |
| Message-ID: | 20230414185632.fdp7sywmz3f627ej@awork3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2023-04-14 13:21:33 -0400, Tom Lane wrote:
> Since the direct I/O commit went in, buildfarm animals
> curculio and morepork have been issuing warnings like
>
> hashpage.c: In function '_hash_expandtable':
> hashpage.c:995: warning: ignoring alignment for stack allocated 'zerobuf'
>
> in places where there's a local variable of type PGIOAlignedBlock
> or PGAlignedXLogBlock. I'm not sure why only those two animals
> are unhappy, but I think they have a point: typical ABIs don't
> guarantee alignment of function stack frames to better than
> 16 bytes or so. In principle the compiler could support a 4K
> alignment request anyway by doing the equivalent of alloca(3),
> but I do not think we can count on that to happen.
Hm. New-ish compilers seem to be ok with it. Perhaps we should have a
configure check whether the compiler is OK with that, and disable direct IO
support if not?
Greetings,
Andres Freund
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