private void returnToPool() {
        try {
            if (pool != null) pool.returnConnection(this);
        } catch (ConnectionException ce) {
            if (logger.isDebugEnabled())
                logger.debug("Returned {} connection to {} but an error occurred - {}", this.getConnectionInfo(), pool, ce.getMessage());
        }
    }
Consider a connection as dead if the underlying channel is not connected.
<p>
Note: A dead connection does not necessarily imply that the server is unavailable. Additional checks
should be performed to mark the server host as unavailable.
gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Connection.java