Re: statistics import and export: another difference in dump/restore

On Wed, Apr 2, 2025 at 10:55 PM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>
> On Wed, 2025-04-02 at 15:35 +0530, Ashutosh Bapat wrote:
> > Once we fix this issue, we need to enable statistics dump and
> > comparison in pg_upgrade/002_pg_upgrade using the attached patch.
>
> The diff appears to be an issue in 002_pg_upgrade.pl introduced in
> 172259afb5. There are two dumps taken from $oldnode: $src_dump is taken
> on line 321, and then $dump_file is taken on line 339. $dump_file is
> used for the restore, but then $src_dump is used for the comparison.
>
> If autovacuum were off, then $src_dump and $dump_file should be the
> same, but autovacuum is not disabled until line 415. Furthermore,
> there's an initdb between lines 321 and 339, allowing autovacuum enough
> time to activate. Otherwise we probably wouldn't have noticed.

Thanks for the analysis. This is useful. I will post a fix on the
original thread. I have assigned myself and fixed the open item entry.

>
> You could disable autovacuum earlier; though not too early, because
> allowing it time to run improves test coverage for stats. Or, you could
> use the same $src_dump for both restoration and comparison, but it
> looks like you wanted coverage of the --create option. (Aside: why
> parallel restore there? Is that just for test coverage or was there a
> performance reason?)

For performance.

--
Best Wishes,
Ashutosh Bapat