koji-hub, event MPM, and postgres max_connections on el8

[Ken Dreyer]

The default RHEL 7 and 8 postgresql.conf ships with "max_connections = 100".

RHEL 7's httpd uses the prefork MPM by default, and RHEL 8's httpd
uses the event MPM by default instead.

It seems that RHEL 8 opens many more simultaneous connections to the
database, and it's very easy to hit PostgreSQL's 100 max_connections
limit. In my tests, it's possible to get ServerOffline errors with
just one or two clients. For example, running kojira with kojiweb will
hit ServerOffline.

When I bump postgresql.conf to "max_connections = 500" I cannot reach
the limit on el8.

Before we tell users to bump this number in the Server HowTo guide,
I'm wondering if there is a better way to improve this in Koji's code.

https://wiki.postgresql.org/wiki/Number_Of_Database_Connections
recommends connection pooling instead of opening more connections, but
I don't know how to implement this.

- Ken

[Michael McLean]

I hacked up a completely naive implementation using psycopg2.pool. It seems
to work ok here on F31, but this would need a lot of clean up.

https://github.com/mikem23/koji-playground/commits/connection-pool

On Fri, May 29, 2020 at 3:27 PM Ken Dreyer <ktdreyer(a)ktdreyer.com&gt; wrote:

>  The default RHEL 7 and 8 postgresql.conf ships with
> "max_connections =
>  100".
>
>  RHEL 7's httpd uses the prefork MPM by default, and RHEL 8's httpd
>  uses the event MPM by default instead.
>
>  It seems that RHEL 8 opens many more simultaneous connections to the
>  database, and it's very easy to hit PostgreSQL's 100 max_connections
>  limit. In my tests, it's possible to get ServerOffline errors with
>  just one or two clients. For example, running kojira with kojiweb will
>  hit ServerOffline.
>
>  When I bump postgresql.conf to "max_connections = 500" I cannot reach
>  the limit on el8.
>
>  Before we tell users to bump this number in the Server HowTo guide,
>  I'm wondering if there is a better way to improve this in Koji's code.
>
>  https://wiki.postgresql.org/wiki/Number_Of_Database_Connections
>  recommends connection pooling instead of opening more connections, but
>  I don't know how to implement this.
>
>  - Ken
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[Michael McLean]

and testing :)

On Fri, May 29, 2020 at 5:23 PM Michael McLean <mikem(a)redhat.com&gt; wrote:

>  I hacked up a completely naive implementation using psycopg2.pool.
> It
>  seems to work ok here on F31, but this would need a lot of clean up.
>
>  https://github.com/mikem23/koji-playground/commits/connection-pool
>
>  On Fri, May 29, 2020 at 3:27 PM Ken Dreyer <ktdreyer(a)ktdreyer.com&gt; wrote:
>
> > The default RHEL 7 and 8 postgresql.conf ships with "max_connections =
> > 100".
> >
> > RHEL 7's httpd uses the prefork MPM by default, and RHEL 8's httpd
> > uses the event MPM by default instead.
> >
> > It seems that RHEL 8 opens many more simultaneous connections to the
> > database, and it's very easy to hit PostgreSQL's 100 max_connections
> > limit. In my tests, it's possible to get ServerOffline errors with
> > just one or two clients. For example, running kojira with kojiweb will
> > hit ServerOffline.
> >
> > When I bump postgresql.conf to "max_connections = 500" I cannot reach
> > the limit on el8.
> >
> > Before we tell users to bump this number in the Server HowTo guide,
> > I'm wondering if there is a better way to improve this in Koji's code.
> >
> > https://wiki.postgresql.org/wiki/Number_Of_Database_Connections
> > recommends connection pooling instead of opening more connections, but
> > I don't know how to implement this.
> >
> > - Ken
> > _______________________________________________
> > koji-devel mailing list -- koji-devel(a)lists.fedorahosted.org
> > To unsubscribe send an email to koji-devel-leave(a)lists.fedorahosted.org
> > Fedora Code of Conduct:
> > https://docs.fedoraproject.org/en-US/project/code-of-conduct/
> > List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines
> > List Archives:
> > https://lists.fedorahosted.org/archives/list/[e-mail]...
> >
>