Neo4j "Can't wait on resource" lock error

Question

I am using Node.js to connect to a hosted GrapheneDB Neo4j database and when attempting to add about 1,500 records I get the following error:

LockClient[19] can't wait on resource 
RWLock[NODE(248), hash=1917331445] since => LockClient[19] 
<-[:HELD_BY]- RWLock[INDEX_ENTRY(153122458561043471), hash=1171319680] 
<-[:WAITING_FOR]- LockClient[15] <-[:HELD_BY]- RWLock[NODE(248), hash=1917331445]

The code that generates this comes from a route that takes a list of JSON objects and then stores them in Neo4j. When importing approx 1,500 records I get this error consistently.

Using seraph-model to do the database accessing and just looking up the record, updating if it exists or creating it if it doesn't.

Any suggestions where to investigate?

Answer 1

It looks like you're doing multiple large transactions concurrently hitting the same region of your graph.

When Neo4j performs a write, a write lock is acquired on that node/relationship and released when the transactions is closed. Other transaction running concurrently who try to acquire a write lock on a already locked entity need to wait - otherwise a box of pandora's inconsistencies would have had opened. If the owner of the lock is a rather long running transaction, the other one might run into a timeout - that would be the above error message.

So you can either:

1. serialize the operations: don't do writes in parallel, instead make sure only one fat transaction is processed at a given time
2. make transactions smaller: if you do less in a singe transaction, the duration will be shorter and other transactions waiting for locks won't timeout.