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

On Mon, Nov 6, 2023 at 4:38 PM Aleksander Alekseev <aleksander(at)timescale(dot)com>
wrote:
> > > PFE the corrected patchset v58.
> >
> > I'd like to revive this thread.
>
> Many thanks for your comments and suggestions.
>
> > I think it worth adding asserts here to verify there is no overflow
making us mapping different segments into the same files.
>
> Sorry, I didn't understand this one. Maybe you could provide the exact
code?

I actually meant this.

static int inline
SlruFileName(SlruCtl ctl, char *path, int64 segno)
{
if (ctl->long_segment_names)
{
/*
* 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.
*/
Assert(segno >= 0 && segno <= 0x1000000000000000);
return snprintf(path, MAXPGPATH, "%s/%015llX", ctl->Dir,
(long long) segno);
}
else
{
Assert(segno >= 0 && segno <= 0x10000);
return snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir,
(unsigned int) segno);
}
}

As I now get, snprintf() wouldn't just truncate the high signs, instead it
will use more characters. But I think assertions are useful anyway.

------
Regards,
Alexander Korotkov