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On Mon, 17 Jan 2000, Peter Koch wrote:
> Hi,
>
> I'm pretty new to this group, and am currently experimenting with
> moving to a linux high availability cluster. Fault tolerance is
> essential, so I'm using a fake linux load balancer, but I also need to
> make sure the database server is fault tolerant also.
>
Well, fault tolerance and high availability are different concepts. I
think fault tolerance should be higher than high availability. If a
service is down for seconds and a minutes and existing connections may be
lost, then the service is up to accept new connections, we can say the
service is highly available. Fault tolerance probably means that once the
connection is accepted, it should be carried out, despite of partial
hardware or software failure.
> Can anyone give me some pointers as to how they are achieving database
> access from the cluster, are you using a dedicated database server, or
> does each server in the cluster have their own local database cache
> that is kept synchronised with distributed transactions. If you are
> using a dedicated database server(s) what is the impact to the cluster
> since now local updates need to be done over the network.
>
If you just want to make a database system of 2 nodes highly available.
You can have a look at http://www.linux-ha.org/ for heartbeat code, the
primary database server and the backup can heartbeat, if the primary
fails, the backup will take over the db service.
If you want to build a highly scalable database cluster, there must be
many works to do. I suggest that you use global storage like GFS to keep
database files, and all database nodes can see those database files. And,
there must be a Distributed Lock Manager to reconcile the conflict when
multiple database nodes want to access the same file or data block
concurrently. Finally, you can use LVS to group all the database nodes for
a single highly scalable database system.
Wensong
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