I encounter an error when attempting the support multiple threads.
I have a graph manager singleton that controls access to a graph and handles
the batching of transactions (committing them only after a set number of
operations). Multiple threads can perform read and write operations
"concurrently", but the graph manager protect concurrent access thought the use
of read/write locks. What I am finding is that a while thread can see a node
that was created by another transaction before the transaction completes, it is
not able to see the properties that were written to it.
The step that are followed are:
Thread 1:
Create a node
Write a property (called _stp_type) to the node
Save the node's ID to a map of ID's by _stp_id (yet another node property)
(the transaction is NOT committed)
Thread 2:
(using the same transaction instance, possibly created by another thread)
Look in the map for the ID of a node with a given _stp_id
Get the node from the graph by ID (graph.getNodeById(id))
Get the _stp_type of that node (graph.getProperty("_stp_type"))
Caused by: org.neo4j.graphdb.NotFoundException: _stp_type property not found
for NodeImpl#4.
at
org.neo4j.kernel.impl.core.Primitive.newPropertyNotFoundException(Primitive.java:172)
at
org.neo4j.kernel.impl.core.Primitive.getProperty(Primitive.java:167)
at
org.neo4j.kernel.impl.core.NodeProxy.getProperty(NodeProxy.java:145)
at com.g1.dcg.graph.neo4j.NeoNode.<init>(NeoNode.java:26)
at com.g1.dcg.graph.neo4j.NeoGraph.toDcgNode(NeoGraph.java:818)
at com.g1.dcg.graph.neo4j.NeoGraph.getNode(NeoGraph.java:1029)
at
com.g1.dcg.graph.neo4j.NeoGraphAutoTx.getNode(NeoGraphAutoTx.java:198)
at
com.g1.component.graph.WriteToGraphStage.execute(WriteToGraphStage.java:93)
... 7 more
I am perfectly willing to accept that what I am doing should not work; I'm just
a little thrown by the fact the I can see the node by not the properties.
Wondering if it is a bug or an invalid use case.
Also, if the proper approach is for each thread to create its own transaction,
then am I correct to assume that uncommitted changes in one thread will not be
visible to the other? Is it then the case that the only way for two threads to
be consistent is to ensure that one thread commits before any other starts its
own transaction?
Thanks.
Paul Jackson, Principal Software Engineer
Pitney Bowes Business Insight
4200 Parliament Place | Suite 600 | Lanham, MD 20706-1844 USA
O: 301.918.0850 | M: 703.862.0120 | www.pb.com
[email protected]
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