Re: jabberd2 questions?

> 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.

> 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.

jack.
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