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From: Nathan Bossart <nathandbossart@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Add a GUC check hook to ensure summarize_wal cannot be enabled when wal_level is minimal
Date: Wed, 10 Jul 2024 09:18:38 -0500
Message-ID: <Zo6YPuvTmRW3b1s7@nathan> (raw)
In-Reply-To: <CA+TgmoansG0B8ayQGw9Ozee6Jawz=HFUACpO_4gp-+SFJBxiYw@mail.gmail.com>
References: <6e30082e-041b-4e31-9633-95a66de76f5d@oss.nttdata.com>
	<ZoVgXuYWbzTLXyRY@nathan>
	<802ff3d5-fdc7-4b08-9046-2e9fc5fdae0e@oss.nttdata.com>
	<CA+TgmoYPNfgAT3OubjoYSiXTb3-urOjQxT3SCEUCrRBx5g6ihA@mail.gmail.com>
	<CA+TgmoY8DnzWNK_xu4=NTYdxGBGnFucrEpOALnS0awMp-s_pKQ@mail.gmail.com>
	<7c1b48d8-0f08-4733-a4e6-d55f04581db7@oss.nttdata.com>
	<CA+TgmoansG0B8ayQGw9Ozee6Jawz=HFUACpO_4gp-+SFJBxiYw@mail.gmail.com>

On Wed, Jul 10, 2024 at 10:10:30AM -0400, Robert Haas wrote:
> On Wed, Jul 10, 2024 at 1:56 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>> I'm sure this patch is necessary as a safeguard for WAL summarization.
>> OTOH, I also think we should apply the patch I proposed earlier
>> in this thread, which prevents summarize_wal from being enabled
>> when wal_level is set to minimal. This way, if there's
>> a misconfiguration, users will see an error message and
>> can quickly identify and fix the issue. Thought?
> 
> I interpreted these emails as meaning that we should not proceed with
> that approach:
> 
> https://www.postgresql.org/message-id/CAGECzQR2r-rHFLQr5AonFehVP8DiFH+==R2yqdBvunYnwxsXNA@mail.gmail...
> http://postgr.es/m/3253790.1720019802@sss.pgh.pa.us

Yeah.  I initially thought this patch might be okay, at least as a stopgap,
but Jelte pointed out a case where it doesn't work, namely when you have
something like the following in the config file:

	wal_level = 'minimal'
	summarize_wal = 'true'
	wal_level = 'logical'

I'm not sure that's a dealbreaker for v17 if we can't come up with anything
else, but IMHO it at least deserves a loud comment and a plan for a better
solution in v18.

-- 
nathan





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  Subject: Re: Add a GUC check hook to ensure summarize_wal cannot be enabled when wal_level is minimal
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