back-llog

Was just thinking we could do a quite simple backend for use with the accesslog overlay and delta-syncrepl. It would write into flat files and do typical logfile rotation on its own. The backing store would have a minimum of two files - one for the suffix entry, one for the current chunk of logs. There would be a configurable number of logfiles, with the oldest simply being deleted when it's time to purge. It would only support Add/Search in general, and Modify on the suffix entry.

A rolling append-only format like this would allow much higher throughput for accesslog recording. Using a binary entry format would of course also help.