Re: XID formatting and SLRU refactorings

On 27/11/2023 01:43, Alexander Korotkov wrote:
> v61 looks good to me. I'm going to push it as long as there are no objections.
This was discussed earlier, but is still present in v61:

> +/*
> + * An internal function used by SlruScanDirectory().
> + *
> + * Returns true if a file with a name of a given length may be a correct
> + * SLRU segment.
> + */
> +static inline bool
> +SlruCorrectSegmentFilenameLength(SlruCtl ctl, size_t len)
> +{
> + if (ctl->long_segment_names)
> + return (len == 15); /* see SlruFileName() */
> + else
> + /*
> + * Commit 638cf09e76d allowed 5-character lengths. Later commit
> + * 73c986adde5 allowed 6-character length.
> + *
> + * XXX should we still consider such names to be valid?
> + */
> + return (len == 4 || len == 5 || len == 6);
> +}
> +

I think it's pretty sloppy that the "short" filenames can be 4, 5 or 6
chars long. For pg_multixact/members, which introduced the 5-char case,
I think we should always pad the filenames 5 characters, and for
commit_ts which introduced the 6 char case, always pad to 6 characters.

Instead of a "long_segment_names" boolean, how about an integer field,
to specify the length.

That means that we'll need pg_upgrade to copy pg_multixact/members files
under the new names. That should be pretty straightforward.

--
Heikki Linnakangas
Neon (https://neon.tech)