Good question, so neo4j implements all the ACID principles of transactions, but that doesn't mean that there's a guarantee that when you've committed a transaction the data is in the store files on disk. In fact that wouldn't be performant at all. The data is written to the store files with buffering or memory mapping depending on environment so when it actually trickles down to actual disk is up to when neo4j decides to "unmap" that area of the store file and when the OS decides to flush its buffers. Instead the only place your transaction is guaranteed to exist on disk after a commit is in the logical log, so for a clean shutdown all the buffers/memory mapped areas of the store files are closed and forced to disk whereas a non-clean shutdown (a crash or whatever) wouldn't do that and there would be no guarantee that all the store file changes would be written. So in case of a non-clean shutdown neo4j must look in the most recently active logical log and replay all those transactions to the store files... and that's what the recovery process does after a non-clean shutdown.
Best, Mattias 2011/10/26 Balazs E. Pataki <pat...@dsd.sztaki.hu> > Hi, > > after crashing my application the next time I start it up I get the usual > > Oct 26, 2011 3:28:42 PM > org.neo4j.kernel.impl.transaction.xaframework.XaLogicalLog > doInternalRecovery > INFO: Non clean shutdown detected on log [/db/nioneo_logical.log.1]. > Recovery started ... > INFO: Non clean shutdown detected on log [/db/index/lucene.log.1]. > Recovery started ... > > kind of messages. > > I have a 8GB database and now this recovery has been running for quite > some time, and I started to thinking why is this recovery is necessary > at all? AS far as I'm aware the transactions are ACID, so they either > commit, or rollback, in both case the state of the database must be OK. > In this case I could see no reason why to do any recovery (from > transactional point of view). If the DB crash happens while transactions > are open, then there coudl be some problems. But in my case I could live > with loosing such transactions and just not have recovery at all. > > To sum up my question: is this doInternalRecovery process essential? And > if not, is there a way to avoid it at startup? > > Thanks, > --- > balazs > > _______________________________________________ > Neo4j mailing list > User@lists.neo4j.org > https://lists.neo4j.org/mailman/listinfo/user > -- Mattias Persson, [matt...@neotechnology.com] Hacker, Neo Technology www.neotechnology.com _______________________________________________ Neo4j mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user
