Re: XID formatting and SLRU refactorings

On Tue, 28 Nov 2023 at 14:37, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:

> On 28/11/2023 12:14, Pavel Borisov wrote:
> > On Tue, 28 Nov 2023 at 13:13, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
> wrote:
> >>
> >> 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.
> >
> > I think what's done in patch 0001 is just an extension of existing
> > logic and moving it into separate function.
>
> That's right. I'm arguing that now is a good time to clean it up.
>
> I won't insist if Alexander prefers to commit it as it is, though. But
> let's at least explain how this works in the comment, instead of the XXX.
>
I agree with you that would be good to add a comment instead of XXX and
commit.

Pavel