[OpenSIPS-Users] [OpenSIPS-Devel] [NEW] Virtual DB module

[Dan Pascu]

On Thursday 30 July 2009, Razvan Pistolea wrote:
> 
> Why a virtual db module?
> 
> 	Until now all modules requiring db support had only one (real) db_url 
connection and it was bad if that connection went down.
> 
> 	Here is where virtual db module comes in: 
> 		it provides to other modules a (virtual) db_url that maps multiple (real) 
db_urls to real dbs.
> 
> 	The real connections are handled transparently to the module using the 
virtual url.
> 	Now if the current real connection goes down the virtual db_url will just 
switch to a new one transparently to the module, giving uninterrupted db 
access.
> 	This mode is called failover and can be used for write and read operations.

How does this work with operations that are separate, but still represent a 
single logical operation, like for example writing usrloc, or dialog data into 
the database not in real time but on a timer, where multiple records are 
inserted at a time. If a connection fails in the middle of an operation, some 
records will end up in one database and some in another and OpenSIPS will have 
troubles finding the information later. Without having transaction support for 
such operations, so that all the inserts that belong together fail and are 
retried together on the next connection, it would be problematic.

Another issue is that even if transaction support would be implemented, there 
is still an uncertainty where the data is. If my usrloc or dialog data was 
saved over multiple connections, after a restart, from where is OpenSIPS 
supposed to read the data?

I can see that this can work fine for read operations assuming that the 
databases are synchronized by external means and wherever you go you get the 
same information, but for write I do not see where the aggregation layer is to 
assure that the data is synchronized and consistent.

-- 
Dan