Re: cluster scaling & performance questiosn

1. What do I do if disk I/O is my contention? CPU?

Adding more nodes could do the trick in both cases. When you add data nodes, you can either increase the number of replicas (better HA) or add the number of node groups. If you increase the number of node groups, full table scans will be distributed over nodes, making it faster. However, simple queries (e.g. using primary key) will be slower as you will more often ask the wrong node group for the data.

    2. If I need more capacity on my read-write heads, do I just add more SQL nodes? Do my apps just need to know of multiple heads?

I would say yes in most cases, until the data nodes are too loaded.

    3. How are simultaneous database writes (updates/inserts) handled? Will I run into locking issues?

You may run into locking issues if you have a lot of concurrent writes, as you would do with any multi-master synchronous replication, or even shared disk (Oracle RAC, PGCluster, PGCluster-II ...). Just think about your application. Does it often modify the same rows ? Does it only write new rows ? Does it mostly read ?

    4. How critical is the management node? If it stops running, what breaks?

The management node is necessary to start or stop nodes. It's also necessary if exactly half of the nodes remains (if you have a cluster with even number of nodes) to keep the cluster running (to avoid split brain, ie having two copies of the database evolving separately). If it stops running, it's not a problem as long as you have more than half of data nodes and at least one replica of each fragment.

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Regards,
Colin Received on Wed Oct 24 03:15:36 2007