Varnish Custom Statistics (VCS) is a data stream management system (DSMS) implementation for Varnish. VCS allows you to analyze the traffic from multiple Varnish servers in real-time to compute traffic statistics and detect critical conditions. This is possible by continuously extracting transactions with the
vcs-key tags in your VSL. Thus, VCS does not slow down your Varnish servers.
VCS collects traffic information from one or more Varnish servers. A typical problem is due to wrong port configuration or firewall rules blocking traffic on the configured ports. You can check connectivity issues by running the
vstatdprobe in the foreground with debugging info:
vstatdprobe -Fg -n <varnish instance name> -p <port vstatd server> <IP address vstatd server>
Details about all possible parameters of
vstatdprobe are available in its man page.
Other typical configuration issue arise when VCS is configured to analyze data from many hours. If you are experiencing high memory usage, you can get an explanation by multiplying the value in
bucket_len \(\cdot\) the number of
vcs-key \(\cdot\) average size of
bytes. A common value for
bytes is around 12KB. If your calculation confirms the size of
bucket_len is the problem, you should reduce it.
As an additional troubleshooting action, we advise you to double check that you have the latest version. For that, please see the VCS installation instructions.