The following error, via bin/neo4j-shell:
Database constraints have changed (txId=84) after this transaction (txId=81) started, which is not yet supported. Please retry your transaction to ensure all constraints are executed.
or as logged in log/debug.log (3.x) or graph.db/messages.log (2.3.x):
2016-10-18 16:40:43.595+0000 ERROR [o.n.s.r.t.TransactionFacade]: Failed to commit transaction.
java.lang.RuntimeException: org.neo4j.kernel.api.exceptions.TransactionFailureException: Database constraints have changed (txId=81) after this transaction
(txId=84) started, which is not yet supported. Please retry your transaction to ensure all constraints are executed.
at org.neo4j.server.rest.transactional.TransitionalTxManagementKernelTransaction.commit(TransitionalTxManagementKernelTransaction.java:87) ~[neo4j-server-2.2.8.jar:2.2.8]
at org.neo4j.server.rest.transactional.TransactionHandle.closeContextAndCollectErrors(TransactionHandle.java:278) [neo4j-server-2.2.8.jar:2.2.8]
can be explained by the following scenario:
[width="80%",options="header"]
|=======
|txID |Date/time | Cypher Statement
|81 | Oct-19-2012 09:00| Begin
|84 | Oct-19-2012 09:01| Begin
|84 | Oct-19-2012 09:02| create constraint on (n:Person) assert n.user_id is unique;
|84 | Oct-19-2012 09:03| Commit
|81 | Oct-19-2012 09:04| create (n:Person {user_id:1234})
|81 | Oct-19-2012 09:05| Commit
|=======
where the exception is thrown at Oct-19-2012 09:05 by the Cypher statement with txID 81 when it tries to create a node which applies to the newly committed constraint, and the transaction is rolled back. Correct remedial action is to resubmit the failed transaction.