It is recently possible to monitor database connection pool statistics:
In JBoss, it is stated that DataSource statistics are disabled by default to minimize performance impact. Is someone aware of how much performance impact there really is?
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Redhat doesn't specify this anywhere. The only way to know for certain would be to run a test in your environment with that setting on the datasource enabled and disabled (not the extension, the Jboss setting itself).
In a very simple test I did I wasn't able to identify anything significant. In the below screenshot the first set of requests is with it enabled and the second is with it disabled. At most there might have been a <1% decrease with it disabled but that wasn't consistent.
Prod level traffic and application specific architecture of course can play a role too. I think they disabled it because in those earlier versions it would be silly to have it being collected by default even with the marginal overhead if it wasn't being used by anyone at all.