McKinley Thank you very much for the detailed explanation. however, I don't get the part about "only one JVM will access database". neo4j doesn't support multiple JVMs has write access to the same db, right?
On Wed, Sep 14, 2011 at 9:14 PM, McKinley <[email protected]> wrote: > If a second thread reads that there is no node with external_id 123 in > between the time that a first thread finds no node and elects to create it, > you will get 2 nodes with external_id 123. So yes, you need to introduce a > lock and synchronize. > > You can create read locks in the graph database but you probably will not > need to do that. In your case you are reading from an index and I am not > sure what locks are available for indexes. If you are running an embedded > database and you can be sure that only your one JVM will access the database > then you can just lock in the Java thread/object space and elect that other > threads must wait to read if the node exists until the first thread has > created it. If you need to communicate concurrency via the database, you > will have to do all the same locking in the Java space and add a read lock > on some control node in Neo4j. > > If you want to create a read lock on a node you can do the following: > > lockManager = graphDb.getConfig().getLockManager(); > lockManager.getReadLock(someNode); > ... > lockManager.releaseReadLock(someNode, null); > > Threading and synchronization in Java will perform great. Depending on your > model, most of the time your node will exist and two or more threads will > just queue up and get the same reference. That waiting is inefficient by > nature, but if your business rules require it then you have to do it. > > Cheers, > > McKinley > > On Wed, Sep 14, 2011 at 12:45 PM, Linan Wang <[email protected]> wrote: > >> hi all, >> I have implemented a function >> UserFactory.get_or_create_with_external_id(long external_id). the >> function basically search the index, see if a node already created and >> has the property "external_id" equals to external_id. if there is such >> a node, return, if not, create one, assign property and index it. >> this function will be called inside of transactions, from unmanaged >> extensions. so it's multi-threaded scenario. >> my question is if i need to mark the function synchronized. my guess >> is true, and i feel it'll hurt performance badly. if my guess is >> wrong, why? thanks >> >> -- >> Best regards >> >> Linan Wang >> _______________________________________________ >> Neo4j mailing list >> [email protected] >> https://lists.neo4j.org/mailman/listinfo/user >> > _______________________________________________ > Neo4j mailing list > [email protected] > https://lists.neo4j.org/mailman/listinfo/user > -- Best regards Linan Wang _______________________________________________ Neo4j mailing list [email protected] https://lists.neo4j.org/mailman/listinfo/user
