Re: Vacuum statistics

On 05.02.2025 09:59, Alexander Korotkov wrote:
> What is the point for disabling pgstat_track_vacuum_statistics then?
> I don't see it saves any valuable resources.  The original point by
> Masahiko Sawada was growth of data structures in times [1] (and
> corresponding memory consumption especially with large number of
> tables).  Now, disabling pgstat_track_vacuum_statistics only saves
> some cycles of pgstat_accumulate_extvac_stats(), and that seems
> insignificant.
>
> I see that we use hash tables with static element size.  So, we can't
> save space by dynamically changing entries size on the base of GUC.
> But could we move vacuum statistics to separate hash tables?  When GUC
> is disabled, new hash tables could be just empty.
>
> Links
> 1.https://www.postgresql.org/message-id/CAD21AoD66b3u28n%3D73kudgMp5wiGiyYUN9LuC9z2ka6YTru5Gw%40mail.gmail.com
>
I understand what you're talking about. I'm looking at the 
pgstat_assoc_relation function and I think that's where I need to decide 
whether we need to allocate memory in the hash table for vacuum 
statistics for them or not.
The same thing happens there depending on the installed 
pgstat_track_counts guc and pgstat_enabled value consequently. Like here:

Specifically, there is an example that for partitions, for example, 
statistics are not accumulated and the condition used like that, like here:

if(!pgstat_track_counts)
{
if(rel->pgstat_info)
pgstat_unlink_relation(rel);
/* We're not counting at all */
rel->pgstat_enabled= false;
rel->pgstat_info= NULL;
return;
}
I think I can try yo add an external parameter in the relation like 
ext_vacuum_pgstat_info and determine its values depending on the guc's 
pgstat_track_vacuum_statisticsvalue.

-- 
Regards,
Alena Rybakina
Postgres Professional