Date: Sun, 5 Feb 2023 15:57:47 -0800
From: Nathan Bossart <nathandbossart@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Michael Paquier <michael@paquier.xyz>, Tom Lane <tgl@sss.pgh.pa.us>,
	Thomas Munro <thomas.munro@gmail.com>,
	Fujii Masao <fujii@postgresql.org>,
	Postgres hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Weird failure with latches in curculio on v15
Message-ID: <20230205235747.GA275913@nathanxps13>
References: <1369666.1675264346@sss.pgh.pa.us>
 <20230201165801.33ydbxvjdbomjqa7@alap3.anarazel.de>
 <20230201175806.GA3199959@nathanxps13>
 <20230201223555.GA3721373@nathanxps13>
 <Y9sam108o4mxZFiS@paquier.xyz>
 <20230204113029.xlcqrbxhp6lerrnc@alap3.anarazel.de>
 <20230204180354.GA258107@nathanxps13>
 <Y979NR3U5VnWrTwB@paquier.xyz>
 <20230205221938.GA274245@nathanxps13>
 <20230205230157.45kl5gqryupzdoyb@alap3.anarazel.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230205230157.45kl5gqryupzdoyb@alap3.anarazel.de>
Archived-At: <https://www.postgresql.org/message-id/20230205235747.GA275913%40nathanxps13>
Precedence: bulk

On Sun, Feb 05, 2023 at 03:01:57PM -0800, Andres Freund wrote:
> I think at the very least you'd want to have a separate callback for
> restoring segments than for restoring other files. But more likely a
> separate callback for each type of file to be restored.
> 
> For the timeline history case an parameter indicating that we don't want
> to restore the file, just to see if there's a conflict, would make
> sense.

That seems reasonable.

> For the segment files, we'd likely need a parameter to indicate whether
> the restore is random or not.

Wouldn't this approach still require each module to handle restoring ahead
of time?  I agree that the shell overhead isn't the main performance issue,
but it's unclear to me how much of this should be baked into PostgreSQL.  I
mean, we could introduce a GUC that tells us how far ahead to restore and
have a background worker (or multiple background workers) asynchronously
pull files into a staging directory via the callbacks.  Is that the sort of
scope you are envisioning?

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com