Statistics enhancements: maxWaitTime and numberOfConnections averages

[vladmihalcea]

I feel we could all benefit from having more detailed statistics, especially if exported through JMX as well. In my current production set-up we have tens of apps (web nodes, import apps, schedulers, each one with a BTM connection pool), all of them concurring for the limited set of database connections.

Trying to set the min and max pool size is more like a wild guess, and I think we can improve this process. For start, we could add more statistics info and make them available through JMX.

1. We could add:

• the cummulativeWaitTime (the time spent in XAPool.getInPool().waitForConnectionInPool())
• the cummulativeConnectionRequestNumber (how many requests have been recorded)

Dividing these two could get us the average wait time.

1. We could also have:

• averageInPoolSize

Currently we have the instant in-pool size info, which is useful, but it changes so rapidly that it makes very difficult to poll it's value and make sure you really calculated a true average. If we set the min and max pool size, we are also interested in the average in-pool size (is it closer to min or to max), so we could better reason on the current pool size settings.