On Aug 19, 2011, at 07:57 , David Rader wrote: > It looks like the HA implementation is for eventual consistency, tunable by > how often a slave polls the master for updates from other nodes. > > With a load balanced cluster, is the best practice to simply use sticky > sessions on clients to ensure that immediate reads of updated data are served > by the same node that wrote the update and are therefore consistent? Any > other recommended approaches?
If your goal is HA, there are two other approaches: 1) Always read from master and 2) Always take read lock on things you read Always reading from master works because writes are synchronously replicated to master, and taking a read lock works because taking a read lock always synchronizes with master (although it of course also disallows related writes for the duration of your transaction). These solutions affect write performance (reading from master consumes master capacity, and taking read locks prevents other transactions from completing). Read performance is certainly affected as well compared to sticky sessions, and is likely to be considerably lower because of the synchronization requirements, and load on master. Consistency guarantees would be as follows: - Reading from arbitrary slaves guarantees very little - Sticky sessions guarantee read-everything-up-until-your-previous-write - Reading from master guarantees consistency re: communications over side channels (if another node, after committing, tells you that he wrote something, you can see that write, or possibly some newer write) - Taking read locks guarantees read-everything-up-until-your-previous-lock-request and also repeatable reads _______________________________________________ Neo4j mailing list [email protected] https://lists.neo4j.org/mailman/listinfo/user
