[reply number 2 - addressing bits I missed in the first reply...] On Wed, 14 May 2008 10:59:33 +0200, "Maurizio Lo Bosco" <maurizio.lobosco@xxxxxx> said: > The dump of the database takes 7 minutes but the disk usage is definitely > low > (less than 5%) A dump of the database visits all records in alphabetical order. This can result in somewhat random looking seeks around the file due to the layout of a skiplist, but it will happen within the mmap. > RedHat is saying that there is no way to optimise the performance on the > GFS > locking architecture and they will now take a look to the cyrus code. You may want to pass on the RedHat engineers that Cyrus uses an MMAP of the entire file to read all records, and uses seeks and direct writes the same fd (or a different fd depending on compilation settings) to write. Skiplist appends entire records to the file, but also seeks back and updates pointers (4 byte records) within the file with each update. That's writing. Reading - it reads each record, gets a pointer to the location of the next one, and reads from the memory location that corresponds to db->map_base + pointer_offset. Depending on your requirements, it may make sense to place your mailboxes.db on local disk (it's pretty small) and regularly copy/rsync it onto your GFS partition. Worst case you lose a couple of mailboxes.db records in a crash. Depends what you can afford to lose. You could probably stat the file every second and copy it on any change pretty cheaply and risk losing at most the last second's changes (it doesn't change often) Regards, Bron. -- Bron Gondwana brong@xxxxxxxxxxx ---- Cyrus Home Page: http://cyrusimap.web.cmu.edu/ Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
