Date: Tue, 25 Jun 2024 17:27:47 -0700
From: Noah Misch <noah@leadboat.com>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Maxim Orlov <orlovmg@gmail.com>,
	Aleksander Alekseev <aleksander@timescale.com>,
	Postgres hackers <pgsql-hackers@lists.postgresql.org>,
	Heikki Linnakangas <hlinnaka@iki.fi>,
	Japin Li <japinli@hotmail.com>, Andres Freund <andres@anarazel.de>,
	Michael Paquier <michael@paquier.xyz>,
	Pavel Borisov <pashkin.elfe@gmail.com>,
	Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Subject: Re: XID formatting and SLRU refactorings (was: Add 64-bit XIDs into
 PostgreSQL 15)
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On Mon, Nov 27, 2023 at 01:43:26AM +0200, Alexander Korotkov wrote:
> v61 looks good to me.  I'm going to push it as long as there are no objections.

This yielded commit 4ed8f09 "Index SLRUs by 64-bit integers rather than by
32-bit integers" and left some expressions coercing SLRU page numbers to int.
Two sources:

  grep -i 'int\b.*page' $(git grep -l SimpleLruInit)
  make && touch $(git grep -l SimpleLruInit) && make PROFILE=-Wconversion 2>&1 | less -p '.int. from .int64. may alter its value'

(Not every match needs to change.)

> --- a/src/include/access/slru.h
> +++ b/src/include/access/slru.h

> @@ -127,7 +127,15 @@ typedef struct SlruCtlData
>  	 * the behavior of this callback has no functional implications.)  Use
>  	 * SlruPagePrecedesUnitTests() in SLRUs meeting its criteria.
>  	 */
> -	bool		(*PagePrecedes) (int, int);
> +	bool		(*PagePrecedes) (int64, int64);
> +
> +	/*
> +	 * If true, use long segment filenames formed from lower 48 bits of the
> +	 * segment number, e.g. pg_xact/000000001234. Otherwise, use short
> +	 * filenames formed from lower 16 bits of the segment number e.g.
> +	 * pg_xact/1234.
> +	 */
> +	bool		long_segment_names;

SlruFileName() makes 15-character (60-bit) file names.  Where does the 48-bit
limit arise?  How does the SlruFileName() comment about a 24-bit limit for
short names relate this comment's 16-bit limit?

nm