Re: Count and log pages set all-frozen by vacuum

On Wed, Oct 30, 2024 at 2:42 PM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
>
> Vacuum currently counts and logs the number of pages of a relation
> with newly frozen tuples. It does not count the number of pages newly
> set all-frozen in the visibility map.
>
> The number of pages set all-frozen in the visibility map by a given
> vacuum can be useful when analyzing which normal vacuums reduce the
> number of pages future aggressive vacuum need to scan.

+1

Some small suggestions:

+ vmbits = visibilitymap_set(vacrel->rel, blkno, buf,
+ InvalidXLogRecPtr,
+ vmbuffer, InvalidTransactionId,
+ VISIBILITYMAP_ALL_VISIBLE |
+ VISIBILITYMAP_ALL_FROZEN);

How about using "old_vmbits" or something along the same lines to make
it clear that this value has the bits before visibilitymap_set()?

---
+ /* If it wasn't all-frozen before, count it */
+ if (!(vmbits & VISIBILITYMAP_ALL_FROZEN))

To keep consistent with surrounding codes in lazyvacuum.c, I think we
can write "if ((vmbits & VISIBILITYMAP_ALL_FROZEN) == 0)" instead.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com