[Serusers] Replication problem

Greger V. Teigre greger at teigre.com
Mon Aug 1 10:38:43 CEST 2005

Hi Andreas,
You are probably one of the people on the list with the most experience with 
replication.  AFAIK, you are correct on all statements below. I assume you 
have SERs on different locations since TCP connect timeout is a problem?
    But I'm not sure why removing the cache would help you?!  Unless you 
want to move to a cluster or DB layer replication?

IMHO, there are only two valid paths for replication in SER: Either develop 
a SIP-layer replication with guaranteed deliveries, queue, non-blocking etc 
(which ends up being proprietary SER) or patch up SER to better be able to 
handle DB-based replication.
I lean towards DB-based replication.  Two prominent things that must be 
handled: Storing the Path information for proper routing of messages to UAs 
behind NAT and a cache that checks the DB if location is not found in 

I would be very interested in patches for this in the experimental CVS 
module ;-)


Andreas Granig wrote:
> Hi all,
> we use DNSSRV balancing and forward_tcp() to replicate registrations
> from one SER to the other SERs in the system.
> Now when one machine completely crashes, all other SER processes on
> all other machines hang when processing a REGISTER until tcp-connect
> times out, leading to a system load of ~16 per machine assuming 16
> child processes per SER, and no other messages can be processed.
> I understand that replicating using UDP would solve this issue, but
> then replicated registrations get lost every now and then because of
> unreliable transmission, and as far as I found out t_replicate() can
> only be used for replicating to *one* other SER.
> This really gets me thinking about patching out the internal location
> cache and lookup every location from memory, because this additional
> lookup really doesn't hurt because of ~10 other DB queries per call.
> IMHO in systems with more than two SERs this cache is just a big pain.
> Andy
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