Re: Options for more aggressive space reclamation in vacuuming?

We regularly vacuum, and *definitely* vacuum after an archive-delete.

On 5/14/23 16:02, Wells Oliver wrote:
> I think our use-case here is nothing special: just very large tables that
> are deleted from and re-inserted with some frequency. They store monthly
> data and exist as partitions. As an example, July of 2022 (summer months
> are peak) had 1,630,558,336 rows. We delete from this and insert daily. We
> rarely get new, relevant data once the month is over. The n_dead_tup
> from pg_stat_all_tables here was over 7m rows, and clearing that out gave
> us back nearly 50GB, and the file size estimate on this partition was ~200
> GB. These tables get auto-vacuumed but clearly it's not, well,
> aggressively reclaiming space.
>
> Given that they are partitions, VACUUM FULL locks the parent table, so new
> writes/deletes can't happen, and anyway people like to run queries against
> these tables quite frequently.
>
> Glad to add any detail I can.
>
> On Sun, May 14, 2023 at 11:32 AM Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>
> On Sun, May 14, 2023 at 1:46 PM Wells Oliver <wells(dot)oliver(at)gmail(dot)com>
> wrote:
>
> Noticed over the last few days how much more space VACUUM FULL
> reclaims (for obvious reasons) and I am wondering if there are any
> solutions for a more fruitful VACUUM without the locks of FULL?
>
>
> There are lots of theories which are all compatible with the minimal
> amount of info given here.  If the space is freed from the indexes,
> then just reindexing (which can be done concurrently in recent
> versions) could reclaim the space. If it is from the table itself then
> something like pg_squeeze
> (https://github.com/cybertec-postgresql/pg_squeeze/) might help. Or
> you can implement your own squeezing, by using a CTE with a ctid scan
> to delete tuples from the end of the table and reinsert them in the
> front, then use regular vacuum to truncate the now-free space off the
> end of the table.
>
> I would think the more fruitful VACUUM would be to prevent the bloat
> from occuring in the first place but without knowing the root cause I
> can't offer anything but platitudes there.
>
> Cheers,
>
> Jeff
>
>
>
> --
> Wells Oliver
> wells(dot)oliver(at)gmail(dot)com <mailto:wellsoliver(at)gmail(dot)com>

--
Born in Arizona, moved to Babylonia.