I’m use the latest versions of the GWT GAE w/ JDO stack.
I have a task queue updating persistent objects with the datastore.
I also have a gwt user interface displaying the save objects (without modification).
Given tightly defined transaction (start/commit) boundaries. Is there a way for me to define a read-only transaction for the GUI that does not conflict with the task updating the objects?
I believe they are conflicting and throwing these exceptions (abridged)
javax.jdo.JDODataStoreException: Transaction rolled back due to failure during commit
at org.datanucleus.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(NucleusJDOHelper.java:402)
at org.datanucleus.jdo.JDOTransaction.commit(JDOTransaction.java:132)
….
NestedThrowablesStackTrace:
java.sql.SQLException: Concurrent Modification
at org.datanucleus.store.appengine.DatastoreTransaction.commit(DatastoreTransaction.java:70)
the app engine datastore actually uses optimistic concurrency (more), not locking. that means that a transaction that does only reads will not interfere or cause contention with other writes or transactions that include writes.