Date: Thu, 03 Mar 2022 11:57:23 +0900 (JST)
Message-Id: <20220303.115723.407686721420998045.horikyota.ntt@gmail.com>
To: melanieplageman@gmail.com
Cc: pgsql-hackers@postgresql.org
Subject: Re: Why do spgbuildempty(), btbuildempty(), and blbuildempty() use
 smgrwrite()?
From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
In-Reply-To: <CAAKRu_b6-NX8OKs02_WRcyuDwf0qBsRa7-Ecp3dGMxKHokzTMQ@mail.gmail.com>
References: <CAAKRu_b6-NX8OKs02_WRcyuDwf0qBsRa7-Ecp3dGMxKHokzTMQ@mail.gmail.com>
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At Wed, 2 Mar 2022 20:07:14 -0500, Melanie Plageman <melanieplageman@gmail.com> wrote in 
> If you enable the CHECK_WRITE_VS_EXTEND-protected assert in mdwrite(),
> you'll trip it anytime you exercise btbuildempty(), blbuildempty(), or
> spgbuildempty().
> 
> In this case, it may not make any meaningful difference if smgrwrite()
> or smgrextend() is called (_mdfd_getseg() behavior won't differ even
> with the different flags, so really only the FileWrite() wait event will
> be different).
> However, it seems like it should still be changed to call smgrextend().
> Or, since they only write a few pages, why not use shared buffers like
> gistbuildempty() and brinbuildempty() do?
> 
> I've attached a patch to move these three into shared buffers.
> 
> And, speaking of spgbuildempty(), there is no test exercising it in
> check-world, so I've attached a patch to do so. I wasn't sure if it
> belonged in spgist.sql or create_index_spgist.sql (on name alone, seems
> like the latter but based on content, seems like the former).
> 
> - Melanie

I didn't dig into your specific isssue, but I'm mildly opposed to
moving them onto shared buffers.  They are cold images of init-fork,
which is actually no-use for active servers.  Rather I'd like to move
brinbuildempty out of shared buffers considering one of my proposing
patches..

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center