When the Java client API reports the connection statistics, there’s one more connection counted in “opened” than “inPool”, even when “inPool” has reached
maxConnsPerNode setting. For example:
Cluster Stats: nodes(inUse,inPool,opened,closed): 21 10.0.0.1 3000 sync(0,4,5,0) async(0,0,0,0)
Why is this the case?
That extra synchronous connection is for tending, the process by which the client library keeps track of which server nodes and partitions are currently available. This is a necessary part of the client functionality and cannot be disabled.
INPOOL INUSE OPENED CLOSED SYNC JAVA CONNECTION TEND