Re: Re: Refresh Publication takes hours and doesn´t finish

[ redirecting to pgsql-hackers as the more relevant list ]

I wrote:
> PegoraroF10 <marcos(at)f10(dot)com(dot)br> writes:
>> I tried sometime ago ... but with no responses, I ask you again.
>> pg_publication_tables is a view that is used to refresh publication, but as
>> we have 15.000 tables, it takes hours and doesn't complete. If I change that
>> view I can have an immediate result. The question is: Can I change that view
>> ? There is some trouble changing those system views ?

> Hmm ... given that pg_get_publication_tables() shouldn't return any
> duplicate OIDs, it does seem unnecessarily inefficient to put it in
> an IN-subselect condition. Peter, is there a reason why this isn't
> a straight lateral join? I get a much saner-looking plan from

> FROM pg_publication P, pg_class C
> - JOIN pg_namespace N ON (N.oid = C.relnamespace)
> - WHERE C.oid IN (SELECT relid FROM pg_get_publication_tables(P.pubname));
> + JOIN pg_namespace N ON (N.oid = C.relnamespace),
> + LATERAL pg_get_publication_tables(P.pubname)
> + WHERE C.oid = pg_get_publication_tables.relid;

For the record, the attached seems like what to do here. It's easy
to show that there's a big performance gain even for normal numbers
of tables, eg if you do

CREATE PUBLICATION mypub FOR ALL TABLES;
SELECT * FROM pg_publication_tables;

in the regression database, the time for the select drops from ~360ms
to ~6ms on my machine. The existing view's performance will drop as
O(N^2) the more publishable tables you have ...

Given that this change impacts the regression test results, project
rules say that it should come with a catversion bump. Since we are
certainly going to have a catversion bump before beta2 because of
the pg_statistic_ext permissions business, that doesn't seem like
a reason not to push it into v12 --- any objections?

regards, tom lane