I'm not sure all of you know, but even earlier syslog-ng versions (2.1 and 2.0) did collect some per-source and per-destination statistics. These were reported periodically in the system log. The problem with this approach that it didn't really scale: with a large configuration the statistics message could become kilobytes long, and parsing this information from a file possibly several gigabytes in size is daunting.
syslog-ng 3.0 has two important changes in this area: it adds several new kinds of counters (like per-host counters), and a UNIX domain socket where you can query the current status of these counters.
As counters certainly have an overhead, you can now control how much statistics you want to gather. The new stats_level() option has three levels for now:
- stats_level(0) is basically the same as earlier syslog-ng versions, per-source and per-destination statistics are kept here. This is the default.
- stats_level(1) adds new counters without a big overhead, that is it adds counters for TCP connections, but does not keep per-host counters
- stats_level(2) adds counters that can have a measurable performance impact, it adds for example per-host (as in $HOST) counters and also keeps track of the time the last message was received from a given host. These counters usually require an hash table lookup in the fastpath.
However if you don't want to dig the logs produced by syslog-ng, you can also use the new UNIX domain socket at /var/run/syslog-ng/syslog-ng.ctl (the path might depend on the compilation options).
If you connect to this socket using netcat (some netcat versions do support UNIX domain sockets), and you send a "STATS" command to it, you get the list of counters.
There are no proper, command line clients for the UNIX domain channel yet, but if you have some scripting ability, you can start gather statistics easily, without the hassles of parsing log files, right after installing a syslog-ng 3.0 snapshot. :)