[Prevayler-discussion] prevayler replication issue

[Edward K. <edw...@gm...>]

Hello.

I decided to use prevayler in a simple diary system which is currently
being used by two law firms in the UK.  It was very liberating to be
able to simply persist my objects without worrying about creating
queries and converting raw data into Java objects... I also considered
some stuff like hibernate, but I realised I simply didn't need a
database at all.  It worked well on the whole, and has been running at
one site for two years now with no problems at all. However, my
colleague recently installed it on another site and we discovered how
the replication mechanism can become unsynchronised... with disastrous
consequences for the client who found herself in court without a
brief!

Firstly, I should say that I know that the replication mechanism is
'still under development' and also perhaps that I have not used
prevayler in exactly the way it was intended to, but I think this is
something people should be aware of.  So... imagine a system with a
main server and several replicas. One of the replicas loses connection
to the main server.  The objects on the replica are still in memory
and can be queried, and the snapshot thread is still running, but when
a transaction is performed on the main server, it is never received by
the replica.  The replica then saves a snapshot and is shut down at
some point and restarted but it never receives the missing transaction
because that predates its latest snapshot.

It's an easy problem to fix of course. Maybe it's old news, but I
can't use 2.3 as I have meddled with the prevayler codebase and it's
way too divergent now... argh maybe I should have gotten myself more
involved earlier and actually contributed something! ;)

Cheers,
Ed