Hi,
On 2021-05-30 03:10:26 +0300, Yura Sokolov wrote:
> While this result is not directly applied to stock PostgreSQL, I believe
> page compression is important for full_page_writes with wal_compression
> enabled. And probably when PostgreSQL is used on filesystem with
> compression enabled (ZFS?).
I don't think the former is relevant, because the hole is skipped in wal page
compression (at some cost).
> Therefore I propose clearing page's empty space with zero in
> PageRepairFragmentation, PageIndexMultiDelete, PageIndexTupleDelete and
> PageIndexTupleDeleteNoCompact.
>
> Sorry, didn't measure impact on raw performance yet.
I'm worried that this might cause O(n^2) behaviour in some cases, by
repeatedly memset'ing the same mostly already zeroed space to 0. Why do we
ever need to do memset_hole() instead of accurately just zeroing out the space
that was just vacated?
Greetings,
Andres Freund