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MountainClimb / datanucleus-appengine

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Transactional operation, and non-transactional operation are not performed in isolation #174

Closed GoogleCodeExporter closed 8 years ago

GoogleCodeExporter commented 8 years ago 
Originally posted here:
http://code.google.com/p/googleappengine/issues/detail?id=2509

Original issue reported on code.google.com by max.r...@gmail.com on 15 Dec 2009 at 5:50

GoogleCodeExporter commented 8 years ago 
Issue 231 has been merged into this issue.

Original comment by googleco...@yahoo.co.uk on 15 Jul 2011 at 3:27

GoogleCodeExporter commented 8 years ago 
From the linked issue

    // this *should* work, but doesn't
    pm1 = pmf.getPersistenceManager();
    pm1.currentTransaction().begin();
    Person p1 = pm1.getObjectById(Person.class, 1);

    pm2 = pmf.getPersistenceManager();  // a second PM
    Person p2 = pm2.getObjectById(Person.class, 2);  // throws exception

This should translate into
    DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
    Transaction txn = ds.beginTransaction();
    Entity e1 = ds.get(personKey1);

    DatastoreService ds2 = DatastoreServiceFactory.getDatastoreService();
    Entity e2 = ds2.get(personKey2);

but doesn't. The "ds2" is just "ds" since DatastorePersistenceHandler is lazy, 
and just uses the same DatastoreService for the majority reads/writes 
regardless of the PersistenceManager that they belong to.

Original comment by googleco...@yahoo.co.uk on 9 Aug 2011 at 6:38

GoogleCodeExporter commented 8 years ago 
I think the underlying issue is that datastore transactions are associated with 
the thread that started them and independent of any particular 
DatastoreService.  Probably no easy fix here.

Original comment by max.r...@gmail.com on 11 Aug 2011 at 3:27

GoogleCodeExporter commented 8 years ago 
The original test is not matching the title of the issue. i.e the second fetch 
is not in a transaction. Consequently it falls into this GAE datastore 
transaction black hole. 

Solution : perform the second fetch in a transaction ... a real explicit 
transaction. This works with SVN trunk when you do

Original comment by googleco...@yahoo.co.uk on 12 Aug 2011 at 6:44