[lvs-users] LVS + Database

Enno Gröper enno+lvs at groeper-berlin.de
Wed Jun 20 10:03:56 BST 2012


Am 19.06.2012 00:00, schrieb YesGood:
> Hi everybody
> The build load balancer cluster of database, in this moment is an
> investigation.
> the response of why are:
>    - I have web server in a load balancer environment, and
>    - I search other system, which can offer load balancing.
>    - I choice database, because it's would be interesting, in a much client
>    environment
>    - and so offer best service.
Using a loadbalanced cluster doesn't automatically mean offering "best
service". Such a cluster introduces a huge amount of complexity,
especially in a database environment. Loadbalancing web servers is
usually no problem.
For having a loadbalanced database cluster you should have a good reason
and some knowhow. Such a good reason would be to _know_, that a single
server just can't manage the load.
If it is for high availability, you don't need to loadbalance. This is a
different usage scenario. Fur high availability you use things like
pacemaker or heartbeat.

> In short of all response receive
>    - build a load balance system of database is possible.
>    - type are:
>       - master-master (both offer write ), is most difficult and
>       complicated. That can be worse than only server.
>       - master-standby (write and only read), only one server the master
>       can receive write request, and other server is standby and only receive
>       read request. But need logic in app. What is it?
If I understand you correctly, you think there is a special app for that?
That is not the case. It's simply, that the applications (PHP scripts
whatever) running on your webservers need to have the logic implemented.
Most applications don't have that and you should just don't do
loadbalancing in that case, as long as you don't really know what you
are doing.

>       - but build a load balance system for database, isn't best choice.
>    Because could offer outdated data Right?
Not only that. You can really screw up your whole database, if you don't
know what you are doing.
The biggest problem is consistency, yes.

>    - Now, are there some references, bibliography that speak about that?
About what? Loadbalancing database servers? The possibilities for that
usually depend on the database management system your are using (MySQL,
pgsql, Oracle, ...). It's a really specific problem.
First you should know what you really need and what you want to do.
Can't your current database server manage the load? Do you want high
availability to decrease the time the server is down?
If you do it wrong, you could even increase the downtime with high
availability due to the complexity this things introduce.
Is this all academic interest or do you need to have some production
system up and running?


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