[Serusers] Replication problem

Klaus Darilion klaus.mailinglists at pernau.at
Mon Aug 1 10:50:29 CEST 2005

Hi Andy!

Another problem: nathelper uses the in memory location table to ping 
natted clients. Thus, also nathelper would have to query the database 
and we need a process to watch the expires and delete outdated entries.


Greger V. Teigre wrote:
> 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 memory.
> I would be very interested in patches for this in the experimental CVS 
> module ;-)
> g-)
> 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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