Re: "multiple backends attempting to wait for pincount 1"

Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2015-02-13 00:27:04 -0500, Tom Lane wrote:

>> I'd say we have a problem. I'd even go so far as to say that
>> somebody has completely broken locking, because this looks like
>> autovacuum and manual vacuuming are hitting the same table at
>> the same time.

> One avenue to look are my changes around both buffer pinning and
> interrupt handling...

I found a way to cause this reliably on my machine and did a
bisect. That pointed to commit 6753333f55e1d9bcb9da4323556b456583624a07

For the record, I would build and start the cluster, start two psql
sessions, and paste this into the first session:

drop table if exists m;
create table m (id int primary key);
insert into m select generate_series(1, 1000000) x;
checkpoint;
vacuum analyze;
checkpoint;
delete from m where id between 50 and 100;
begin;
declare c cursor for select * from m;
fetch c;
fetch c;
fetch c;

As soon as I saw the fetches execute I hit Enter on this in the
other psql session:

vacuum freeze m;

It would block, and then within a minute (i.e., autovacuum_naptime)
I would get the error.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company