From: Michael Paquier <michael@paquier.xyz>
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Georgios <gkokolatos@protonmail.com>
Cc: Julien Rouhaud <julien.rouhaud@free.fr>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: robertmhaas@gmail.com <robertmhaas@gmail.com>
Subject: Re: Shared memory size computation oversight?
Date: Thu, 4 Mar 2021 17:21:35 +0900
Message-ID: <YECYj2KORHb06xbA@paquier.xyz> (raw)
In-Reply-To: <20210304072333.4yydog47md7cfrda@nol>
References: <20210227080815.jryyhy6lrn6gahkm@nol>
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<1183451.1614788634@sss.pgh.pa.us>
<20210303164052.f336wina7qpchabd@nol>
<YECGppkDKJArPOUb@paquier.xyz>
<20210304072333.4yydog47md7cfrda@nol>
On Thu, Mar 04, 2021 at 03:23:33PM +0800, Julien Rouhaud wrote:
> I was also considering adding new (add|mull)_*_size functions to avoid having
> too messy code. I'm not terribly happy with xxx_shm_size(), as not all call to
> those functions would require an alignment. Maybe (add|mull)shmemalign_size?
>
> But before modifying dozens of calls, should we really fix those or only
> increase a bit the "slop factor", or a mix of it?
>
> For instance, I can see that for instance BackendStatusShmemSize() never had
> any padding consideration, while others do.
>
> Maybe only fixing contribs, some macro like PredXactListDataSize that already
> do a MAXALIGN, SimpleLruShmemSize and hash_estimate_size() would be a short
> patch and should significantly improve the estimation.
The lack of complaints in this area looks to me like a sign that we
may not really need to backpatch something, so I would not be against
a precise chirurgy, with a separate set of {add,mul}_size() routines
that are used where adapted, so as it is easy to track down which size
estimations expect an extra padding. I would be curious to hear more
thoughts from others here.
Saying that, calling a new routine something like add_shmem_align_size
makes it clear what's its purpose.
--
Michael
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To: pgsql-hackers@postgresql.org
Cc: michael@paquier.xyz, rjuju123@gmail.com, tgl@sss.pgh.pa.us, gkokolatos@protonmail.com, julien.rouhaud@free.fr, pgsql-hackers@lists.postgresql.org, robertmhaas@gmail.com
Subject: Re: Shared memory size computation oversight?
In-Reply-To: <YECYj2KORHb06xbA@paquier.xyz>
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