Database threading with Scala futures (Play2)

Question

I'm developing a Scala Play2 application that queries an OrientDB Graph in Scala Play2. Until today I didn't bother with indexes and all seemed to work fine but now that I have enabled a couple I get this error:

play.api.http.HttpErrorHandlerExceptions$$anon$1: Execution exception[[ODatabaseException: Database instance is not set in current thread. Assure to set it with: ODatabaseRecordThreadLocal.INSTANCE.set(db);]]

From the documentation I understand that the database object is not thread safe but I'm uncertain how to proceed: my queries are picked up asynchronously by the Play2 executor pool and I'm not sure whether it would be a good idea to mess around with threadlocals. Will the driver block? Will the driver clobber its state if different threads from the pool handle the database connection? In any case I would like some advice from someone that knows Orient's driver architecture better than me :)

Answer 1

As suggested by the documentation and the error, the OrientDB driver uses thread locals to isolate thread-unsafe portions of itself.

The solution to this issue was to move away from the simplistic design I had at that point and run the queries from within an org.apache.tinkerpop.gremlin.orientdb.OrientGraph acquired through a org.apache.tinkerpop.gremlin.orientdb.OrientGraphFactory#getTx() called within the same block.

I didn't investigate whether a transaction is strictly required, although I don't think so.