Hello,
(cross-posting being something I want to get developers and users express their opinions).
We were recently in a (lucky) situation to have two new modules submissions targeting more or less the same purpose: allowing to use Kamailio with a Redis backend via database API.
One was submitted by Andreas Granig (Sipwise) and already merged with the name db_redis, because it was designed from the beginning as a generic DB connector, so the module can be used with auth_db, acc, usrloc, ...
* https://www.kamailio.org/docs/modules/devel/modules/db_redis.html
The second one was submitted by Surendra Tiwari (Plivo), initially having a naming conflict with db_redis, but renamed to db_redisusrloc, see the pull request at:
* https://github.com/kamailio/kamailio/pull/1446
Now, this email is about deciding the way to go forward with the second module.
It was designed to be used only for usrloc in the first phase, with many specific usrloc attributes hard coded inside db_redisusrloc. Surendra said (in a private chat) that the long term plan is to make it work for other modules. Anyhow, at this moment is very tied to usrloc, therefore the name of the module.
Given that the backend (Redis) is not an SQL engine, mapping over Kamailio's DB API needs some schema definition (see the readme of db_redis) in order to make it generic and work for all our modules that use a DB backend.
On the other hand, to squeeze the best of the backend, specially in no-SQL cases, having a dedicated DB connector module optimized for a specific module might help to get more performances/high-availability/scalability from the backend itself.
In this case, for example the expires value for a contact record can be set inside redis, so kamailio module doesn't have to run a timer routine to clean up (it doesn't mean db_redisusrloc does it right now, I didn't have time for a proper review, just giving an example). Surendra said they use it in production for couple of months now and it is several times faster than using usrloc with db_postgres (iirc, not db_mysql) for db_mode=3 (database only mode).
But of course, the reverse of the medal with a dedicated db connector for a module: it adds overhead to code maintenance (besides generic updates due to external library changes, I expect changing something relevant in usrloc, like adding new columns, would require updates in this module as well).
So, there are few things I want feedback on:
1) how do you fill about splitting from a generic-only DB connectors to have also some dedicated ones? This is more from confusion point of view, as a general rule so far, we do not deny contributions if there are other options for same kind of feature (e.g., many lcr or nat traversal options). As long as the contributor is willing to maintain the code, we were fine.
2) I guess usrloc, presence and dialog modules would be the main suspects that would benefit for such dedicated connectors, in other cases might not worth adding dedicated connectors. Missing any other module one would like to squeeze more performances with a dedicated connector?
3) should we set a different naming policy for such modules, for example: use *dbs_* prefix instead *db_*, to suggest better it is a DataBase Specific connector?
4) Andreas said he plans to do some performance testing of usrloc module with the two modules and see the differences. Anyone else that wants to do it? It can be a good metric to see if it worth going one way or another?
5) Helping to review the pull request, specially if you use Redis, is appreciated. Personally I am very short in available time these days, next week I plan do to new Kamailio stable releases, so the schedule is not getting lighter in my side.
Cheers, Daniel