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 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