Re: jabberd2 questions?

On Thu, 28 Aug 2008, Jack Moffitt wrote:
>> I am trying to find out if Jabberd2 Server can support 3000 concurrent
>> users. Does anybody know or has done any testing to find out how many
>> concurrent users can Jabberd2 support?
>
>I imagine this is possible, but latency from the database load is
>likely going to make it not so great.

The database doesn't need to be on the same machine as the jabberd2
processes.  We're using a MySQL cluster and believe that this will
hopefully be enough to serve ~10000, but we're still in a pilot phase.

According to Simon Yeo, jabberd2 has been used to serve 15k users
successfully[1].  Our installation has a similar distribution among
servers.

>> If it cannot support so many users what are the issues due to which it
>> cannot scale? What part of the Jabberd2 core needs to be fixed in order
>> for it to scale?
>
>The limiting factor j2 scalability is the session manager (sm)
>component.  While you can spread the server components out over
>multiple machines and run multiple copies of some components (like
>c2s), sm cannot be distributed at all.  A single machine must be able
>to handle all the sessions of the server.
>
>Also, there are several memory leaks in the session manager that
>affected us severely at Chesspark.  We had to restart the session
>manager (and thus the entire server) about once every two weeks, even
>with only a few hundred simultaneous users.   I'm not sure if the leak
>is exacerbated by our particular usage patterns, but I can't imagine
>how often you'd need to restart for 3,000 simultaneous users.
>
>In addition, if you are using relational database storage as the
>backend, even light use of the database can cause noticably packet
>latency since the non-blocking server design of j2 is marred by the
>blocking database calls.  Also, j2 only uses a single database
>connection instead of a connection pool.
>
>If you plan to scale j2, you will need to implement some kind of
>database pooling and find and fix the memory leaks if they affect your
>usage patterns.  I'm sure that with these issues fixed, the j2 session
>manager could handle 3,000 simultaneous users.  Perhaps you'd have to
>add in some memcache to the mix, but that is fairly trivial compared
>to the other tasks.
>
>Bottom line, if I was a consultant and you were my client, I would be
>steering you away from jabberd2 and onto something different.  Since
>my server administration experience has been mainly with jabberd2, I
>do not have an alternative suggestion for you, except to say that
>we've migrated to ejabberd at Chesspark and have been very happy with
>it over the last week.

We have not yet run into the memory leak, for whatever reason, but we've
only been serving ~50 simultaneous users so far during the pilot.

Your experience worries me.

>jack.

-Derek.

[1]
<http://mailman.jabber.org/pipermail/jadmin/2006-September/098513.html>
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