After upgrade to a Splunk 6.2 indexer cluster, why do searches hang with high memory consumption and we're forced to restart?

Hi, We've recently upgraded to a Splunk 6.2 indexer cluster, but we're finding that searches will hang and the system goes unresponsive. We're forced to restart the entire system. Our hardware doesn't spikes, but Memory consumption is high (as normal). Is there any diagnostic we can run after we've successfully restarting the system to find out what the root cause was? Thanks, Ryan