Safe, Sequential And Scalable Counters In Mnesia

Question

I am writing an application in Erlang/OTP and want to use sequential counters on a version recording system.

I first implemented them with

mnesia:dirty_update_count         


        

Answer 1

Well, since Mnesia data is not guaranteed to replicate atomicly you have to manually lock somehow. I see three alternatives (two with locking and one without):

• Using read locks on the table as you request a new version number. That implies transactions though.

• Use a central server that keeps track of the version numbers and increment them atomically, for example by having a process on one of your nodes which you ask for version numbers.

• Synchronize your servers with NTP and use timestamps.