The READ COMMITTED level is partially incorrect depending on what order read
and write locks are acquired by the transactions. The following code allows
uncommitted values to be seen (it is part of a junit test).
TreeCache cache =new TreeCache();
cache.setCacheMode(TreeCache.LOCAL);
cache.setTransactionManagerLookupClass("org.jboss.cache.DummyTransactionManagerLookup");
cache.setIsolationLevel(IsolationLevel.READ_COMMITTED);
cache.createService();
cache.startService();
TransactionManager mgr = cache.getTransactionManager();
//transaction 1
mgr.begin();
cache.put(Fqn.fromString("test"),"testKey","test");
mgr.commit();
// transaction 2
mgr.begin();
cache.get(Fqn.fromString("test"),"testKey");
Transaction tx = mgr.getTransaction();
mgr.suspend();
// transaction 3
mgr.begin();
cache.put(Fqn.fromString("test"),"testKey2","test");
Object obj =cache.get(Fqn.fromString("test"),"testKey");
Object obj2 =cache.get(Fqn.fromString("test"),"testKey2");
assertNotNull(obj);
assertNotNull(obj2);
Transaction tx2 = mgr.getTransaction();
mgr.suspend();
// transaction 2
mgr.resume(tx);
Object obj3 =cache.get(Fqn.fromString("test"),"testKey");
Object obj4 =cache.get(Fqn.fromString("test"),"testKey2");
assertNotNull(obj3);
System.out.println(obj3);
assertNull(obj4);
mgr.commit();
mgr.resume(tx2);
mgr.commit();
The second block of transaction 2 can see the data that has been put into the
node by tx1 even though tx1 has not committed yet. (The assertNull(obj4) fails).
However, if I do this:
//transaction 1
mgr.begin();
cache.put(Fqn.fromString("test"),"testKey","test");
mgr.commit();
// transaction 2
mgr.begin();
cache.put(Fqn.fromString("test"),"testKey2","test");
Transaction tx = mgr.getTransaction();
mgr.suspend();
// transaction 3
mgr.begin();
// cache.put(Fqn.fromString("test"),"testKey2","test");
Object obj =cache.get(Fqn.fromString("test"),"testKey");
Object obj2 =cache.get(Fqn.fromString("test"),"testKey2");
assertNotNull(obj);
assertNotNull(obj2);
Transaction tx2 = mgr.getTransaction();
mgr.suspend();
The get in transaction 3 for the testKey2 uncommitted value behaves as expected
by throwing an exception as it cannot acquire a readlock on the node.
It appears that if I acquire a readlock first for TxA then a writelock for TxB
I can ignore the isolation level and it effectively becomes NONE.
View the original post :
http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3909755#3909755
Reply to the post :
http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&p=3909755
-------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
for problems? Stop! Download the new AJAX search engine that makes
searching your log files as easy as surfing the web. DOWNLOAD SPLUNK!
http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click
_______________________________________________
JBoss-user mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/jboss-user
