Text from the page linked by toppk, dated 2017-10-10 and about macOS Sierra:
Apple’s grand design... fills a single unified log with many hundreds or thousands of log entries every minute. As Apple’s team stated in their 2016 presentation “we want as much logging on all the time as possible”.
Log contents are stored as tracev3 files – an undocumented compressed binary format – in /var/db/diagnostics/Persist/ and /var/db/diagnostics/Special/. Other folders in
/var/db/diagnostics/and/var/db/uuidtext/contain ancillary information for those logs.
/var/db/uuidtext/contains a series of folders, named 00 to FF, each containing files named by UUID for specific log events, which extend beyond normal log entries. These include crash events and other items which overflow single line entries in the log. There is another folder nameddscwhich contains similar files.