Today we log slow processing of outbound messages like this:

sending transport message [Request{indices:data/write/bulk[s][r]}{123456}{false}{false}{false}] of size [1234] on [Netty4TcpChannel{localAddress=/99.99.99.99:9999, remoteAddress=99.99.99.99/99.99.99.99:9999, profile=default}] took [12345ms] which is above the warn threshold of [5000ms] with success [true]

The took time records the time until the message is completely written to the channel, which includes time spent waiting for the channel to become writeable as well as time spent waiting for the transport thread to get around to the transmission. We care about the latter (it indicates a bug) much more than the former (it indicates network saturation). It would be good to distinguish these two causes.