Ability to know which servers are currently in the pool about twemproxy HOT 3 CLOSED

It is possible to answer which servers are not in the pool looking by looking at the following stats
https://github.com/twitter/twemproxy/blob/master/src/nc_stats.h#L38
https://github.com/twitter/twemproxy/blob/master/src/nc_stats.h#L38
https://github.com/twitter/twemproxy/blob/master/src/nc_stats.h#L38

• server_eof is incremented when the server close the connection normally (which should not happen because we use persistent connection)
• server_timedout is incremented when the connection / request to server timedout
• server_err is incremented for any other kinds of error

So, on a given server, the cumulative number of times server is ejected can be computed as (server_err + server_timedout + server_eof) / server_failure_limit

A diff of the above value between two successive minutes would give you a nice timeseries graph

from twemproxy.

Also if you run twemproxy with "-v 6" option you would see the following log line when a server is ejected.

https://github.com/twitter/twemproxy/blob/master/src/nc_server.c#L278

from twemproxy.

updated notes here: https://github.com/twitter/twemproxy/blob/master/notes/recommendation.md#graphing-cache-pool-state

from twemproxy.