I am having three custom defined search handlers for Solr 4. It works fine, however I want to know whether it has any impact on RAM & CPU utilization and overall performance when considering an index size of 10 gb with replication setup.
I do not find any documentation on this. Any idea would be great.
Or do you recommend to stick to default handlers or use single handlers? Why?
Just by defining more request handler, no you should not have a performance impact. As quoted from the Reference Docs
A request handler is a Solr plug-in that defines the logic to be used when Solr processes a request.
So a request handler is the blueprint of processing logic to perform, when a request comes in. Just by defining more ways how this can be handled does not bear a performance impact. Of course this could be a matter of numbers. If you define hundreds or thousands of handlers that could have an impact. I just never saw such a configuration.
The operations that consume CPU and RAM are operations that interact with the index, like searching and indexing. When your clients start using the new request handlers, you will see a grown consumption in resources. But this is due to the usage by the client, not the mere definition of the way how to consume.