[OpenSIPS-Users] [OpenSIPS-Devel] [Fwd: Re: [NEW] Virtual DB module]

[Iñaki Baz Castillo]

2009/7/31 Dan Pascu <dan at ag-projects.com>:
> On Thursday 30 July 2009, Razvan Pistolea wrote:
>> 2. Synchronization between dbs will be lost.
>>
>> 3b.        use database managers (that know how to merge databases)
>> 3c.        use a cluster db
>
> That sounds good in theory, but in practice fails in so many ways. I've worked
> with this for years and even after so much time bidirectional database
> replication is extremely fragile and fails easily. Just one example:
>
> You start writing to db1, it performs the operation just fine, but right after
> it finished and is about to return you the success response to your query you
> lose the connection. If never see the answer, assume it failed and go on to
> write the record to db2, which succeeds as well and also returns the answer.
> Now you have the same record in both databases and when they will try to
> replicate from each other they'll fail. The problem gets even worse with
> multiple databases that replicate from each other.
>
> This is not just a theoretical example. I've seen this on a constant basis
> when performing a simple operation like heartbeat stop on the master to move
> the services to the slave, while somebody writes into the database as the same
> time (like for example opensips writing accounting requests for something as
> modest as 1.5 calls per second). This is so common, that you can consider
> yourself lucky if replication is not broken between the 2 databases when you
> stop one to activate the other, without taking measures to stop the influx of
> write operations to them during the switch.

Very good points. master-master replication or master-slave becoming
inactive-master is really a pain, I've also suffered it a lot.

I wonder if filesystem based replication (i.e. BRBD) is a more
reliable choice even if it could seem fragile (it's a binary
replication, so a single error could entirely corrupt the database).
About it, I've listened every kind of opinions, so... :)



-- 
Iñaki Baz Castillo
<ibc at aliax.net>