Re: XID formatting and SLRU refactorings (was: Add 64-bit XIDs into PostgreSQL 15)

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
itsvalue'
 

(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