Each secondary node maintains an INC connection pool. The connection pool manages connections from the secondary node to the coordinator node used by INC for transactional communication.
The INC connection pool reduces communication overhead by re-using existing connections rather than opening new ones, and controls how many INC connections may be established by a secondary node to the coordinator at the same time.
The maximum number of connections to be allowed to be open from a secondary node to the coordinator, MPX_MAX_CONNECTION_POOL_SIZE.
The maximum number of unused connections to be kept alive when the connection is returned to the unused pool, MPX_MAX_UNUSED_POOL_SIZE.