Re: Autovacuum on partitioned table

On Fri, Feb 21, 2020 at 4:47 PM Masahiko Sawada
<masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> Thank you for updating the patch. I tested v4 patch.
>
> After analyze or autoanalyze on partitioned table n_live_tup and
> n_dead_tup are updated. However, TRUNCATE and VACUUM on the
> partitioned table don't change these values until invoking analyze or
> autoanalyze whereas in normal tables these values are reset or
> changed. For example, with your patch:
>
> * Before
> relname | n_live_tup | n_dead_tup | n_mod_since_analyze
> ---------+------------+------------+---------------------
> c1 | 11 | 0 | 0
> c2 | 11 | 0 | 0
> c3 | 11 | 0 | 0
> c4 | 11 | 0 | 0
> c5 | 11 | 0 | 0
> parent | 55 | 0 | 0
> (6 rows)
>
> * After 'TRUNCATE parent'
> relname | n_live_tup | n_dead_tup | n_mod_since_analyze
> ---------+------------+------------+---------------------
> c1 | 0 | 0 | 0
> c2 | 0 | 0 | 0
> c3 | 0 | 0 | 0
> c4 | 0 | 0 | 0
> c5 | 0 | 0 | 0
> parent | 55 | 0 | 0
> (6 rows)
>
> * Before
> relname | n_live_tup | n_dead_tup | n_mod_since_analyze
> ---------+------------+------------+---------------------
> c1 | 0 | 11 | 0
> c2 | 0 | 11 | 0
> c3 | 0 | 11 | 0
> c4 | 0 | 11 | 0
> c5 | 0 | 11 | 0
> parent | 0 | 55 | 0
> (6 rows)
>
> * After 'VACUUM parent'
> relname | n_live_tup | n_dead_tup | n_mod_since_analyze
> ---------+------------+------------+---------------------
> c1 | 0 | 0 | 0
> c2 | 0 | 0 | 0
> c3 | 0 | 0 | 0
> c4 | 0 | 0 | 0
> c5 | 0 | 0 | 0
> parent | 0 | 55 | 0
> (6 rows)
>
> We can make it work correctly but I think perhaps we can skip updating
> statistics values of partitioned tables other than n_mod_since_analyze
> as the first step. Because if we support also n_live_tup and
> n_dead_tup, user might get confused that other statistics values such
> as seq_scan, seq_tup_read however are not supported.

+1, that makes sense.

Thanks,
Amit