Re: pg_verify_checksums and -fno-strict-aliasing

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Michael Paquier <michael(at)paquier(dot)xyz>, Michael Banck <michael(dot)banck(at)credativ(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_verify_checksums and -fno-strict-aliasing
Date: 2018-09-01 05:24:38
Message-ID: alpine.DEB.2.21.1809010716470.32764@lancre
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Hello,

>> Okay, for the memo replay_image_masked and master_image_masked
>> in xlog.c could make use of the new structure. SetWALSegSize in
>> pg_standby.c and WriteEmptyXLOG in pg_resetwal.c, and pg_upgrade's
>> file.c could also be patched.
>
> I intentionally didn't change replay_image_masked/master_image_masked
> to use statically-allocated buffers. Since, AFAICS, those aren't
> needed in most backend processes, they'd just be eating 16KB of
> per-process data space to no purpose.
>
> The others you mention could be changed, probably, but I didn't
> bother as they didn't seem performance-critical.

I'd go for having just one same approach everywhere, for code base
homogeneity.

>>> +typedef union PGAlignedBuffer
>
>> One complain I have is about the name of those structures. Perhaps
>> PGAlignedBlock and PGAlignedXlogBlock make more sense?
>
> Don't have a strong preference, anybody else have an opinion?

I like "Block" better, because it's more precise.

> (I also wondered whether to use "WAL" instead of "XLog" in that
> struct name, but it seems like we've mostly stuck with "xlog"
> in internal C names.)

Best to blend with the surrounding code in the header file?

--
Fabien.

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