Re: Hot Standby Conflict on pg_attribute

On Fri, May 10, 2019 at 12:41 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

Andres Freund <andres@anarazel.de> writes:
> On 2019-05-09 13:03:50 -0700, Erik Jones wrote:
>> The question then is: Why would these user queries be waiting on an
>> AccessShare lock on pg_attribute?

> Queries that access a table for the *first* time after DDL happened
> (including truncating the relation), need an AccessShareLock on
> pg_attribute (and pg_class, pg_index, ...) for a short time.

Also, it seems likely that what's really triggering the issue is
autovacuum on pg_attribute trying to truncate off empty pages
in pg_attribute (after a bunch of dead rows were generated there
by DDL activity).  That requires exclusive lock on pg_attribute,
which would propagate down to the standby.

                        regards, tom lane

Right, that part I understood after checking out pg_attribute's insert/delete counts in pg_stat_sys_tables before and after some REFRESH MATERIALIZED VIEW runs on an otherwise idle server.  With them running 2k+ refreshes per day autovac is regularly working on their catalog tables.

Thanks!

--

Erik Jones
mage2k@gmail.com