Messages can be attached to maps or map items. A message consists of a time-stamp, a time interval, a tag and a text string. Messages are only kept for a short period in memory. 

Messages can also be saved in files. Every message is prepended with the message time-stamp and the message interval.

Messages are saved in files if two conditions are met. First, the associated item or map must have a non-empty -path option. Second, the message tag must match one of the patterns contained in the value of the -store option. The -store option is a convenient way to select which messages go to a file and which not.

The file name is derived from the value of the -path option. It is constructed from the -path value by appending a subdirectory for the current day and the message tag as a file name. 

The message text itself is prepended by the time-stamp (in seconds), a tab character, the time interval, another tab character and appended to the file. New directories are created on the fly if needed.

As an example, lets assume we have a map where the -path option has the value /tamp/yourmap and the -store option contains the list element “ifload*”. A message is generated on May 27th, 1997 with the tag ifload-3 and the text “52”. This message will be appended to the file /tmp/yourmap/1997-05-27/ifload-3.

Messages provide a convenient mechanism to collect statistics. However, message files can consume quite a bit of disk space. No attempts are made to compress raw message files and there are currently no commands to read and process them later via Tcl in a convenient way. Compression, data reduction or analysis of the statistics should be done by specialized programs, which are run periodically.