Hi!
On 12.05.2025 08:30, Amit Kapila wrote:
> On Fri, May 9, 2025 at 5:34 PM Alena Rybakina <a.rybakina@postgrespro.ru> wrote:
>> I did a rebase and finished the part with storing statistics separately from the relation statistics - now it is
possibleto disable the collection of statistics for relationsh using gucs and
>> this allows us to solve the problem with the memory consumed.
>>
> I think this patch is trying to collect data similar to what we do for
> pg_stat_statements for SQL statements. So, can't we follow a similar
> idea such that these additional statistics will be collected once some
> external module like pg_stat_statements is enabled? That module should
> be responsible for accumulating and resetting the data, so we won't
> have this memory consumption issue.
The idea is good, it will require one hook for the pgstat_report_vacuum
function, the extvac_stats_start and extvac_stats_end functions can be
run if the extension is loaded, so as not to add more hooks.
But I see a problem here with tracking deleted objects for which
statistics are no longer needed. There are two solutions to this and I
don't like both of them, to be honest.
The first way is to add a background process that will go through the
table with saved statistics and check whether the relation or the
database are relevant now or not and if not, then
delete the vacuum statistics information for it. This may be
resource-intensive. The second way is to add hooks for deleting the
database and relationships (functions dropdb, index_drop,
heap_drop_with_catalog).
> BTW, how will these new statistics be used to autotune a vacuum?
yes, but they are collected on demand - by guc.
> And
> do we need all the statistics proposed by this patch?
>
Regarding this issue, it was discussed here and so far we have come to
the conclusion that statistics are needed for a deep understanding of
the work of vacuum statistics [0] [1] [2].
[0]
https://www.postgresql.org/message-id/0B6CBF4C-CC2A-4200-9126-CE3A390D938B%40upgrade.com
[1]
https://www.postgresql.org/message-id/6732acf8ce0f31025b535ae1a64568750924a887.camel%40moonset.ru
[2]
https://www.postgresql.org/message-id/5AA8FFD5-6DE2-4A31-8E00-AE98F738F5D1%40upgrade.com
--
Regards,
Alena Rybakina
Postgres Professional
