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

Hi,

> > Reviewing this now. I think it's almost ready to be committed.
> >
> > There's another big effort going on to move SLRUs to the regular buffer
> > cache (https://commitfest.postgresql.org/43/3514/). I wonder how moving
> > to 64 bit page numbers will affect that. BlockNumber is still 32 bits,
> > after all.
>
> Somehow I didn't pay too much attention to this effort, thanks. I will
> familiarize myself with the patch. Intuitively I don't think that the
> patchse should block each other.
>
> > This patch makes the filenames always 12 characters wide (for SLRUs that
> > opt-in to the new naming). That's actually not enough for the full range
> > that a 64 bit page number can represent. Should we make it 16 characters
> > now, to avoid repeating the same mistake we made earlier? Or make it
> > more configurable, on a per-SLRU basis. One reason I don't want to just
> > make it 16 characters is that WAL segment filenames are also 16 hex
> > characters, which could cause confusion.
>
> Good catch. I propose the following solution:
>
> ```
> SlruFileName(SlruCtl ctl, char *path, int64 segno)
> {
> if (ctl->long_segment_names)
> - return snprintf(path, MAXPGPATH, "%s/%012llX", ctl->Dir,
> + /*
> + * We could use 16 characters here but the disadvantage would be that
> + * the SLRU segments will be hard to distinguish from WAL segments.
> + *
> + * For this reason we use 15 characters. It is enough but also means
> + * that in the future we can't decrease SLRU_PAGES_PER_SEGMENT easily.
> + */
> + return snprintf(path, MAXPGPATH, "%s/%015llX", ctl->Dir,
> (long long) segno);
> else
> return snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir,
> ```
>
> PFE the corrected patchset v58.

While triaging the patches for the September CF [1] a consensus was
reached that the patchset needs another round of review. Also I
removed myself from the list of reviewers in order to make it clear
that a review from somebody else would be appreciated.

[1]: https://postgr.es/m/0737f444-59bb-ac1d-2753-873c40da0840%40eisentraut.org
--
Best regards,
Aleksander Alekseev