2014-12-17, 02:23
The log will always overwrite any existing file, that's by design. Flushing just prevents the OS from buffering output. If you want separate files for each run, you can specify @logfile.unique=yes which will append a random number to the log file name, or of course specify your own unique filename for each run with @logfile=. There is no support for appending to an existing log file.