Rails applications tend to be very verbose in their logging. Instiki is no exception. By default, this branch of Instiki rotates its logfile (logs/production.log) whenever the logfile grows to about 1MB in size, keeping the last 25 files. This log rotation feature is built into the standard Ruby Logger class. The precise parameters can be customized in config/environments/production.rb.
N.B.: Log Rotation does not seem to work on (some?) Windows installations. Instead, when Instiki tries to rotate the log file, a 500 Application Error occurs. See the workaround here.
Instiki uses action caching. For the most part, Instiki is smart about clearing the cache. There are, however, times when, despite the best of intentions, the cache becomes stale.
If you have commandline access, deleting the corresponding file(s) in the cache/view/ directory will do the trick. Otherwise, try editing the offending page, and that will expire the cache.