[SR-Users] Kamailio delayed reponse in case of database load

[Alex Balashov]

Ali,

If Kamailio is performing a database-bound workload, there's no way to
make it respond faster if the database is being slow. Excluding things
like caching of route responses, how would that be logically possible?
:-)

Since we use PostgreSQL (and prefix_range) very extensively, I can say
that such extreme slow-downs when loading data are abnormal; relational
databases in general, and Postgres's MVCC in particular, are
specifically designed to deal with concurrently servicing intensive read
operations amidst bulk writes. Speculating purely a priori, these delays
are probably caused by very high I/O demand of a slow storage subsystem;
you can attempt to ascertain that by running 'iostat -x 1' while loading
the new data and looking at percentage utilisation on the relevant
storage interface, or with 'iotop' or similar tools.

But if the database responds slowly due to high background I/O load,
you can't make Kamailio render an answer any faster. About the only
thing you can do is to try mitigate the negative effects of this on the
SIP level:

(1) Send a '100 Trying' pre-emptively before initiating the query; this
will dampen the retransmissions that otherwise occur, and whose
proliferation could cause a positive feedback loop and deepen your
problems in a database slow-down scenario;

(2) Do asynchronous processing of the SQL query with t_suspend() /
t_continue() -- though, you should carefully weigh the downsides of this
given the (small) additional overhead of suspending/resuming every
transaction under normal operating conditions.

For more background on this topic, consider a look at my blog post on
the subject from some years ago:

http://www.evaristesys.com/blog/tuning-kamailio-for-high-throughput-and-performance/

Hope that helps!

Cheers,

-- Alex

PS. You may wish to escape the value of '$rU' and not lift it directly
into your SQL queries, e.g. 

https://www.kamailio.org/wiki/cookbooks/5.3.x/transformations#sescapecommon

https://www.kamailio.org/wiki/cookbooks/5.3.x/transformations#sqlval

Otherwise, you may be exposing yourself to a possible SQL injection
attack, i.e. if I get creative with what I put in the user part of the
request URI in a way that doesn't jam Kamailio's SIP parser.

-- 
Alex Balashov | Principal | Evariste Systems LLC

Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) 
Web: http://www.evaristesys.com/, http://www.csrpswitch.com/