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

On Tue, May 21, 2019 at 4:42 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> [ redirecting to pgsql-hackers as the more relevant list ]
>
> I wrote:
> > PegoraroF10 <marcos@f10.com.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?
>

I completely agree to push it into v12.