I'm writing on behalf of the HikariCP project. We're thrilled to see HikariCP included as a configuration pool option for exoCR (though it would be great if it were the default):

http://docs.jboss.org/exojcr/1.16.0-GA/developer/en-US/html/chapter-Kernel.html#Kernel.HikariCP

Though we are concerned a bit about the example configuration given creating a pool of 600 connections. We have a short but concise write-up on connection pool sizing where we make a compelling argument that a connection pool larger than a few dozen connections – even for workloads of 10k simultaneous users running 20k transactions per second – causes degradation of performance:

https://github.com/brettwooldridge/HikariCP/wiki/About-Pool-Sizing

We would be pleased if you read it, and if you agree, adjust the pool size in your example configuration.

Thanks,
The HikariCP Project Team