defines if the ETag generation algorithm will use the modified-time value of the file.
If you have multiple lighttpd servers serving static content then you should use
etag.use-mtime = "disable"
So that the ETag value is consistent across the lighttpd clusters. Otherwise you will generate lesser number of 304 responses
Do make sure that the static content on all your clusters have the same mtime (modified-time) if you intend to enable this option