Query using Optimistic Locking

Hello all ,
"With optimistic locking, a resource is not actually locked when it is first is accessed by a transaction."
Is optimistic locking used for banking applications ??
Please share your ideas , share your ideas.Thanks in advance.

Can optimistic locking be used for banking applications? Sure. Is it always appropriate for every possible banking related application? No.
You'll need to be a lot more specific about your application's requirements before we can say anything with much specificity. In general, banking or non-banking, OLTP applications ought to be using optimistic locking and any application that uses pessimistic locking needs to be careful not to hold locks across user interaction events (i.e. don't allow a user to lock a row and then head out to lunch without releasing the lock).
Justin

Similar Messages

How to use Optimistic Locking in Toplink

Hi!
Iam using Toplink for O/R mapping, and for each table
iam using one TimeStamp field, and i specified that
field as Locking filed, by using the Loking option, and checked the TimeStampLocking option.
Now my question is do i need to update the Timestamp filed
each time if i create a new record and while modify an existing record.
And also do i need to compare the Timestamp for the record which client as read previousley to the TimeStamp in the database for the record manullay lik
suppose t1 is the timeStamp, which i got from the client,
and t2 is the timestamp which i read from the Database.
Now my question is, is it necessary to compare the timestamp.

Once optimistic locking has been configured TopLink will manage the updating and comparing of the OptimisticLocking value. There is no requirement for you to manage this value.
--Gordon

Em.merge does not throw Optimistic Lock Exception

Hello,
we are using Optimistic Lock Exception in a stateful bean managed transaction.
I am wondering that there is no Optimistic Lock Exception is thrown after em.merge
The Optimistic Lock Exception is primary thrown on em.flush - is this right?
A similar problem is described on
http://www.nabble.com/Optimistic-Lock-Exception-expected-td22742662.html#a22742662
See serveroutput: The EclipseLink-5006-Exception is thrown after an em.flush
14:03:11,657 INFO [STDOUT] updateItem
14:03:11,657 INFO [STDOUT] [EL Finest]: 2009-04-09 14:03:11.657--UnitOfWork(14218007)--Thread(WorkerThread#0[192.168.1.217:4518])--Merge clone with references com.tup.model.Person@131a24c
14:03:11,657 INFO [STDOUT] merged
14:03:11,657 INFO [STDOUT] [EL Finest]: 2009-04-09 14:03:11.657--UnitOfWork(14218007)--Thread(WorkerThread#0[192.168.1.217:4518])--Execute query UpdateObjectQuery(com.tup.model.Person@196649c)
14:03:11,657 INFO [STDOUT] [EL Fine]: 2009-04-09 14:03:11.657--ClientSession(21268424)--Connection(25845065)--Thread(WorkerThread#0[192.168.1.217:4518])--UPDATE mku_person_ver SET first_name = ? WHERE ((ID = ?) AND (((last_name = ?) AND (first_name = ?)) AND (version = ?)))
bind => [Bernd 982, 5, Kuls, Bernd 98, 2009-04-09 13:12:15.0]
14:03:11,672 INFO [STDOUT] [EL Warning]: 2009-04-09 14:03:11.672--UnitOfWork(14218007)--Thread(WorkerThread#0[192.168.1.217:4518])--Exception [EclipseLink-5006] (Eclipse Persistence Services - 1.1.0.r3634): org.eclipse.persistence.exceptions.OptimisticLockException
Exception Description: The object [com.tup.model.Person@196649c] cannot be updated because it has changed or been deleted since it was last read.
Class> com.tup.model.Person Primary Key> [5]
14:03:11,688 INFO [STDOUT] [EL Warning]: 2009-04-09 14:03:11.688--UnitOfWork(14218007)--Thread(WorkerThread#0[192.168.1.217:4518])--javax.persistence.OptimisticLockException: Exception [EclipseLink-5006] (Eclipse Persistence Services - 1.1.0.r3634): org.eclipse.persistence.exceptions.OptimisticLockException
Exception Description: The object [com.tup.model.Person@196649c] cannot be updated because it has changed or been deleted since it was last read.
Class> com.tup.model.Person Primary Key> [5]
14:03:11,688 INFO [STDOUT] OptimisticLockException throws MyApplicationException
14:03:11,688 INFO [STDOUT] MyApplicationException
14:03:11,735 INFO [STDOUT] [EL Finer]: 2009-04-09 14:03:11.735--UnitOfWork(14218007)--Thread(WorkerThread#0[192.168.1.217:4518])--TX afterCompletion callback, status=ROLLEDBACK
14:03:11,750 INFO [STDOUT] [EL Finer]: 2009-04-09 14:03:11.75--UnitOfWork(14218007)--Thread(WorkerThread#0[192.168.1.217:4518])--release unit of work
14:03:11,750 INFO [STDOUT] [EL Finer]: 2009-04-09 14:03:11.75--ClientSession(21268424)--Thread(WorkerThread#0[192.168.1.217:4518])--client released
14:03:11,750 ERROR [BMTInterceptor] BMT stateful bean 'ModelFacade' did not complete user transaction properly status=STATUS_MARKED_ROLLBACK
And by this Exception the transaction's status is set to status=STATUS_MARKED_ROLLBACK.
The transaction can no longer be used.
I want to use this transaction further and wrap the OptimisticLockException into an MyApplicationException
(see serveroutput).
But no change!
Any Ideas ?
Regards,
Martin Kubitza
T&P Bochum/Germany

Hi,
are you using JPA or TopLink ? Check if there is another exception thrown that produces the error. You can try and catch (Exception ex), which will catch them all. if this works the obviously you don't catch the right exception
I found a post saying that: "If you trying commit directly after persist w/o doing an explicit
flush then OptimisticLocking Exception maybe nested inside
RollBackException. What is the top most error on stack? You can catch
javax.persistence.PersistenceException and try to do this kind of
error translation
public static void getThrowable(javax.persistence.PersistenceException
perex, int code) {
boolean updateError = false ;
boolean deleteError = false ;
KentException kentex = null ;
Throwable th = null ;
if( perex instanceof org.apache.openjpa.persistence.RollbackException) {
th = perex.getCause();
if(th instanceof OptimisticLockException) {
updateError = true ;
if(perex instanceof OptimisticLockException ){
updateError = true ;
th = perex ;
if(perex instanceof org.apache.openjpa.persistence.EntityNotFoundException) {
deleteError = true ;
th = perex ;
http://n2.nabble.com/OptimisticLockException-confusion.-td210621.html
Frank

Toplink Optimistic Locking not working with Session Bean facade.

I am working on Oracle JDeveloper v 10.1.2 and connecting to an Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - 64bit
The application is based on J2EE architecture and the technology stack uses Struts for presentation/controller framework, Stateless Session EJBs as session facade for custom business services, Simple java classes for the business services, Toplink implementation of DAO layer, Domain objects are mapped to database tables using Toplink Workbench that ships with JDeveloper. The transaction is managed by the session bean and hence the toplink session is configured to use external transaction controller and a named datasource as follows.
<session xsi:type="server-session">
<name>DBSession</name>
<server-platform xsi:type="oc4j-1012-platform"/>
<event-listener-classes/>
<logging xsi:type="toplink-log">
<log-level>fine</log-level>
<file-name>D:/ToplinkLog.log</file-name>
</logging>
<primary-project xsi:type="xml">META-INF/toplink-descriptor.xml</primary-project>
<login xsi:type="database-login">
<platform-class>oracle.toplink.platform.database.oracle.Oracle10Platform</platform-class>
<external-connection-pooling>true</external-connection-pooling>
<external-transaction-controller>true</external-transaction-controller>
<sequencing>
<default-sequence xsi:type="native-sequence">
<name>Native</name>
<preallocation-size>1</preallocation-size>
</default-sequence>
</sequencing>
<datasource>jdbc/ORADS</datasource>
</login>
</session>
We intend to use Optimistic Locking based on Timestamp-version locking through an audit field "last_modification_date" of type java.sql.Timestamp. The corresponding database field is also of type Timestamp(6). We are not storing the version in cache.
The problem we are facing is as follows.. we have an edit screen from where user can edit values for a domain object which are then persisted using Toplink...we expect Toplink to check the database record version (modification_date timestamp) before it applies the update. In DAO implementation, we register the object in a unitOfWork, then set the modified values, however we leave the modification_date (version field) unedited. Now when the application is running, on edit, an exception is thrown by the Session bean before ending the transaction.
com.evermind.server.rmi.OrionRemoteException: Transaction was rolled back: Error in transaction: java.lang.NullPointerException
     at TrackingMediator_StatelessSessionBeanWrapper2.editOverheadExpenditure(TrackingMediator_StatelessSessionBeanWrapper2.java:1597)
     at com.enbridge.dsm.web.action.TrackingPortfolioAction.editOverheadExpenditure(TrackingPortfolioAction.java:264)
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     at java.lang.reflect.Method.invoke(Method.java)
     at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:278)
     at com.enbridge.dsm.web.shared.BaseAction.execute(BaseAction.java:90)
     at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:465)
     at com.enbridge.dsm.web.shared.DSMPojoRequestProcessor.process(DSMPojoRequestProcessor.java:182)
     at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1425)
     at com.sourcebeat.strutslive.common.SLActionServlet.process(SLActionServlet.java:44)
     at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:760)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
     at com.evermind.server.http.ResourceFilterChain.doFilter(ResourceFilterChain.java:65)
     at oracle.security.jazn.oc4j.JAZNFilter.doFilter(Unknown Source)
     at com.evermind.server.http.EvermindFilterChain.doFilter(EvermindFilterChain.java:16)
     at com.enbridge.dsm.web.shared.security.SecurityFilter.doFilter(SecurityFilter.java:142)
     at com.evermind.server.http.ServletRequestDispatcher.invoke(ServletRequestDispatcher.java:645)
     at com.evermind.server.http.ServletRequestDispatcher.forwardInternal(ServletRequestDispatcher.java:322)
     at com.evermind.server.http.HttpRequestHandler.processRequest(HttpRequestHandler.java:790)
     at com.evermind.server.http.HttpRequestHandler.run(HttpRequestHandler.java:270)
     at com.evermind.server.http.HttpRequestHandler.run(HttpRequestHandler.java:112)
     at com.evermind.util.ReleasableResourcePooledExecutor$MyWorker.run(ReleasableResourcePooledExecutor.java:192)
     at java.lang.Thread.run(Thread.java:534)
     Nested exception is:
java.lang.NullPointerException
     at oracle.jdbc.driver.PhysicalConnection.commit(PhysicalConnection.java:1190)
     at com.evermind.sql.FilterConnection.commit(FilterConnection.java:209)
     at com.evermind.sql.DriverManagerXAConnection.commit(DriverManagerXAConnection.java:203)
     at com.evermind.server.TransactionEnlistment.commit(TransactionEnlistment.java:251)
     at com.evermind.server.ApplicationServerTransaction.singlePhaseCommit(ApplicationServerTransaction.java:745)
     at com.evermind.server.ApplicationServerTransaction.commit(ApplicationServerTransaction.java:690)
     at com.evermind.server.ApplicationServerTransaction.end(ApplicationServerTransaction.java:1035)
     at TrackingMediator_StatelessSessionBeanWrapper2.editOverheadExpenditure(TrackingMediator_StatelessSessionBeanWrapper2.java:1593)
     at com.enbridge.dsm.web.action.TrackingPortfolioAction.editOverheadExpenditure(TrackingPortfolioAction.java:264)
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     at java.lang.reflect.Method.invoke(Method.java)
     at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:278)
     at com.enbridge.dsm.web.shared.BaseAction.execute(BaseAction.java:90)
     at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:465)
     at com.enbridge.dsm.web.shared.DSMPojoRequestProcessor.process(DSMPojoRequestProcessor.java:182)
     at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1425)
     at com.sourcebeat.strutslive.common.SLActionServlet.process(SLActionServlet.java:44)
     at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:760)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
     at com.evermind.server.http.ResourceFilterChain.doFilter(ResourceFilterChain.java:65)
     at oracle.security.jazn.oc4j.JAZNFilter.doFilter(Unknown Source)
     at com.evermind.server.http.EvermindFilterChain.doFilter(EvermindFilterChain.java:16)
     at com.enbridge.dsm.web.shared.security.SecurityFilter.doFilter(SecurityFilter.java:142)
     at com.evermind.server.http.ServletRequestDispatcher.invoke(ServletRequestDispatcher.java:645)
     at com.evermind.server.http.ServletRequestDispatcher.forwardInternal(ServletRequestDispatcher.java:322)
     at com.evermind.server.http.HttpRequestHandler.processRequest(HttpRequestHandler.java:790)
     at com.evermind.server.http.HttpRequestHandler.run(HttpRequestHandler.java:270)
     at com.evermind.server.http.HttpRequestHandler.run(HttpRequestHandler.java:112)
     at com.evermind.util.ReleasableResourcePooledExecutor$MyWorker.run(ReleasableResourcePooledExecutor.java:192)
     at java.lang.Thread.run(Thread.java:534)
Note that the exception is thrown at the time when the session bean is about to commit the transaction. i.e. the DAO code did not throw any exception and was able to check the optimistic locking and submit the update transaction.
I am not able to understand why is the the EJB throwing this weird error with Optimistic locking implementation. The application is working fine when the optimistic locking is disabled.
I am facing another problem due to this problem... since the session bean throws this exception after exiting the bean implemented method, when trying to commit the transaction, I am not able to mark the session context to setRollbackOnly. Hence if I continue on to another transaction by navigating to another screen in the application, mysteriously the previous transaction gets committed!!... again... weird...

I am using JDBC driver version 10.1.2.
I saw this additional error message in JDeveloper console, which for some reason was not logged to my log4j log file... if it helps...
06/09/22 18:32:10 Thr[thread 6]-TransactionEnlistment.TransactionEnlistment.Caught forgetandRollback XAException e null
Here are the logs from my Toplink log file....
[TopLink Info]: 2006.09.22 06:31:46.546--ServerSession(989)--Thread(Thread[HttpRequestHandler-86,5,main])--TopLink, version: Oracle TopLink - 10g Release 3 (10.1.3.0.0) (Build 060118)
[TopLink Info]: 2006.09.22 06:31:46.578--ServerSession(989)--Thread(Thread[HttpRequestHandler-86,5,main])--Server: Oracle Application Server Containers for J2EE 10g (10.1.2.0.0)
[TopLink Config]: 2006.09.22 06:31:46.593--ServerSession(989)--Connection(991)--Thread(Thread[HttpRequestHandler-86,5,main])--connecting(DatabaseLogin(
     platform=>Oracle10Platform
     user name=> ""
     connector=>JNDIConnector datasource name=>jdbc/ORADS
[TopLink Config]: 2006.09.22 06:31:47.484--ServerSession(989)--Connection(1432)--Thread(Thread[HttpRequestHandler-86,5,main])--Connected: jdbc:oracle:thin:@10.210.16.37:1521:orabld
     User: APP_USR
     Database: Oracle Version: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
     Driver: Oracle JDBC driver Version: 10.1.0.3.0
[TopLink Config]: 2006.09.22 06:31:47.500--ServerSession(989)--Connection(1433)--Thread(Thread[HttpRequestHandler-86,5,main])--connecting(DatabaseLogin(
     platform=>Oracle10Platform
     user name=> ""
     connector=>JNDIConnector datasource name=>jdbc/ORADS
[TopLink Config]: 2006.09.22 06:31:47.500--ServerSession(989)--Connection(1434)--Thread(Thread[HttpRequestHandler-86,5,main])--Connected: jdbc:oracle:thin:@10.210.16.37:1521:orabld
     User: APP_USR
     Database: Oracle Version: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
     Driver: Oracle JDBC driver Version: 10.1.0.3.0
[TopLink Info]: 2006.09.22 06:31:47.671--ServerSession(989)--Thread(Thread[HttpRequestHandler-86,5,main])--DBSession login successful
[TopLink Fine]: 2006.09.22 06:31:47.703--ServerSession(989)--Connection(1554)--Thread(Thread[HttpRequestHandler-86,5,main])--select * from user_role ur, app_resource ar, role_resource rr where rr.APP_RESOURCE_ID = ar.APP_RESOURCE_ID and rr.USER_ROLE_ID = ur.USER_ROLE_ID
[TopLink Fine]: 2006.09.22 06:31:49.937--ServerSession(989)--Connection(10245)--Thread(Thread[HttpRequestHandler-86,5,main])--SELECT * FROM PROGRAM_SUB_CAT
[TopLink Fine]: 2006.09.22 06:31:50.015--ServerSession(989)--Connection(10332)--Thread(Thread[HttpRequestHandler-86,5,main])--SELECT PROGRAM_ID, CREATED_BY_USERID FROM (SELECT CREATED_BY_USERID, ROWNUM PROGRAM_ID FROM (SELECT DISTINCT(CREATED_BY_USERID) CREATED_BY_USERID, 1 AS PROGRAM_ID FROM PROGRAM))
(I only see my application specific queries after this... no exceptions or debug logs)... as I said before.. the application gives exception in the session bean at the time of commit, and there's no exception raised from Toplink code in DAO...

Optimistic Locking fails when version field is part of a Aggregate

I'm trying to persist a Mapped Object using 9.0.3 Toplink.
The object uses optimistic locking while the Timestamp versioning field is part of an Aggreate Descriptor. This works well in the Workbench (does not complain).
Unfortunally it does not work whenever I use the UnitOfWork to register and commit the chances.
Sample code:
Object original;
UnitOfWork unitOfWork = ...
Object clone =   unitOfWork.registerExistingObject(original);
clone.setBarcode("bliblalbu");
unitOfWork.commit();This throws an nasty OptimisticLockException, complaining about a missing versioning field:
LOCAL EXCEPTION STACK:
EXCEPTION [TOPLINK-5004] (TopLink - 9.0.3 (Build 423)): oracle.toplink.exceptions.OptimisticLockException
EXCEPTION DESCRIPTION: An attempt was made to update the object [BusinessObject:{id:12382902,shorttext:null,barcode:bliblablu,ownerLocation:null,IdEntryName:0,idCs:20579121}], but it has no version number in the identity map.
It may not have been read before the update was attempted.
CLASS> de.grob.wps.domain.model.BusinessObjectBO PK> [12382902]
     at oracle.toplink.exceptions.OptimisticLockException.noVersionNumberWhenUpdating(Unknown Source)
     at oracle.toplink.descriptors.VersionLockingPolicy.addLockValuesToTranslationRow(Unknown Source)
     at oracle.toplink.internal.queryframework.DatabaseQueryMechanism.updateObjectForWrite(Unknown Source)
     at oracle.toplink.queryframework.WriteObjectQuery.executeCommit(Unknown Source)
     at oracle.toplink.internal.queryframework.DatabaseQueryMechanism.executeWrite(Unknown Source)
     at oracle.toplink.queryframework.WriteObjectQuery.execute(Unknown Source)
     at oracle.toplink.queryframework.DatabaseQuery.execute(Unknown Source)
     at oracle.toplink.publicinterface.Session.internalExecuteQuery(Unknown Source)
     at oracle.toplink.publicinterface.UnitOfWork.internalExecuteQuery(Unknown Source)
     at oracle.toplink.publicinterface.Session.executeQuery(Unknown Source)
     at oracle.toplink.publicinterface.Session.executeQuery(Unknown Source)
     at oracle.toplink.internal.sessions.CommitManager.commitAllObjects(Unknown Source)
     at oracle.toplink.publicinterface.Session.writeAllObjects(Unknown Source)
     at oracle.toplink.publicinterface.UnitOfWork.commitToDatabase(Unknown Source)
     at oracle.toplink.publicinterface.UnitOfWork.commitRootUnitOfWork(Unknown Source)
     at oracle.toplink.publicinterface.UnitOfWork.commitAndResume(Unknown Source)
     at de.grob.wps.dwarf.domainstore.toplink.ToplinkTransaction.commit(ToplinkTransaction.java:60)
     at de.grob.wps.dwarf.domainstore.toplink.ToplinkPersistenceManager.commit(ToplinkPersistenceManager.java:396)
     at de.grob.wps.dwarf.domainstore.toplink.ToplinkPersistenceManagerTest.testPersistSerializableWithBusinessObjects(ToplinkPersistenceManagerTest.java:87)
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     at java.lang.reflect.Method.invoke(Method.java:324)
     at junit.framework.TestCase.runTest(TestCase.java:154)
     at junit.framework.TestCase.runBare(TestCase.java:127)
     at junit.framework.TestResult$1.protect(TestResult.java:106)
     at junit.framework.TestResult.runProtected(TestResult.java:124)
     at junit.framework.TestResult.run(TestResult.java:109)
     at junit.framework.TestCase.run(TestCase.java:118)
     at junit.framework.TestSuite.runTest(TestSuite.java:208)
     at junit.framework.TestSuite.run(TestSuite.java:203)
     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:392)
     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:276)
     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:167)So what can I to fix this problem? BTW the Object I try to persists has been read from database and the IDE debugger shows what that the aggregate object contains java.sql.Timestamp instances.

Sorry guys. My debugger fooled me. The locking field wasn't initialized in the database. This caused the problem which is fixed now.
Thx anyway.
Bye
Toby

High concurrency optimistic locking

Hi there,
We have an EJB method that roughly does the following; we have a number of buckets that may or may not be full. If one or more are not full we want it to find the one with the most space available and add the item there. Our main problem here is that this method can be called upwards of 1000 times per second and we're now looking for an efficient way to solve the concurrency issue of two different calls both thinking bucket X has space left even though one of the two calls will fill it up :
THREAD 1 : findEmptyBucket() returns BUCKET1 (1 SPOT LEFT)
THREAD 2 : findEmptyBucket() returns BUCKET1 (1 SPOT LEFT)
THREAD 1 : addItemToBucket(BUCKET1) <- FULL NOW
THREAD 2 : addItemToBucket(BUCKET1) <- WRONG
Since only optimistic locking is available in the spec for some reason I think the "EJB3" approach is basically (pseudoish) :
while(!succeeded) {
    try {
        Bucket b = findEmptyBucket(...); // Will throw OptimisticLockException?
        addItemToBucket(b, item);
        succeeded = true;
    catch(OptimisticLockException e) {}
} This seems horribly inefficient for a call that is almost guaranteed to require dozens of retries during peak hours. Is there any way to optimize this in such a way that we don't have to use optimistic locking? We're trying to solve this without using vendor specific solutions but EJB3 seems to lack the necessary functionality. Suggestions definitely welcome, evne if they are "that's the only way to do it" ;)
Thanks!

I think the OptimisticLockingException is thrown after-the-fact. So, if the addItemToBucket() method does a commit (flush), it will generate the exception rather than the find method. Otherwise, if there is no explicit commit call, the exception will be thrown when the EJB method that holds the while loop returns.
If performance is critical, maybe a Stateful SessionBean with a Stateless Facade would work better. Create a Stateless SessionBean with an addItem() method and a reference to a single stateful bean. The implementation of the stateful session bean would be something like the following standalone program. The stateful bean would have an addItem() method too, but would keep track of a pool of resources internally.
class ItemBucket { Item i; }
class Item { String data; }
class NoBucketsAvailableException extends Exception {}
public class bucket {
    final static int POOL_SIZE = 4;
    ItemBucket[] bucketPool = new ItemBucket[POOL_SIZE];
    Object[] bucketLocks = new Object[POOL_SIZE];
    void initBucketPool() {
     for(int i=0; i<POOL_SIZE; i++) {
         bucketPool[i] = new ItemBucket();
         bucketLocks[i] = new Object();
    void addItemToEmptyBucket(Item _i) throws NoBucketsAvailableException {
     int i=0;
     for(; i<POOL_SIZE; i++) {
         if( bucketPool.i == null ) { // possible empty bucket
          synchronized(bucketLocks[i]) {
          if( bucketPool[i].i == null ) { // double checked locking
               bucketPool[i].i = _i;
     if( i >= POOL_SIZE) { throw new NoBucketsAvailableException(); }
public static void main(String[] args) {
     bucket app = new bucket();
     app.initBucketPool();
     Item item = new Item();
     item.data = "test";
     try {
     app.addItemToEmptyBucket(item);
     catch(NoBucketsAvailableException exc) {}

Aggregate-collection-mapping combined with optimistic-locking

I've tried to set up an aggregate-collection-mapping and everything seems to be okay. But one thing still lacks: use this aggregate-collection in combination with optimistic-locking. Defining to use optimistic-locking (exactly: timestamp locking) doesn't work. The generated sql-statement doesn't have the wanted timestamp field. Any idea is recommend.

Hi,
Aggregate collection mappings do support optimistic locking. You MUST map and store the version value in the object, not the cache. Aggregate objects are not cache independently of their parents so cannot store their version value in the cache.
Make sure that you have:
- provided a direc-to-field (non-readonly) mapping for the version field
- define the locking policy to store the version value in the object, not the cache
Example:
     descriptor.descriptorIsAggregateCollection();
     descriptor.useTimestampLocking("VERSION", false);
     // SECTION: DIRECTTOFIELDMAPPING
     DirectToFieldMapping directtofieldmapping3 = new DirectToFieldMapping();
     directtofieldmapping3.setAttributeName("version");
     directtofieldmapping3.setIsReadOnly(false );
     directtofieldmapping3.setFieldName("VERSION");
     descriptor.addMapping(directtofieldmapping3);

ChangeFields optimistic locking

I am trying to use optmistic locking without changing my database schema by using the descriptor.useChangedFieldsLocking() on my EJB descriptor. Two clients try to do the following.
1) Query the shallow properties of the EJB (no getters called for unary or collection relationships).
2) Edit some of that simple data
3) Submit their changes
The optimistic locking works okay when just the shallow properties are being retrieved. If a client tries to submit when someone else has already done so, an OptimisticLockException is thrown which is the desired result.
However, if I wish to traverse one of the relationships on the EJB when it is first queried (by calling a getter for a collection for example) the following happens: When the second client attempts to load and edit this EJB the transaction times out with a deadlock exception.
I want to traverse relationships for display purposes in this case but in the furture will want to edit something in that relationship with ChangedFieldsLocking also set.
If anyone could tell me why the second client's transaction times out when it asks for the EJB I would be very grateful.
Regards
James.

Thanks for the reply.
After further investigation I have found that it's nothing to do with the locking (since I can switch it off and still have the problem) but may be a problem with OC4J (or how I am using it). The situation is as follows:
1) Client A starts a transaction
2) Client A asks for ejb1
3) Client A asks for ejb1.collection()
4) Client A asks for ejb1.collection(i).someMethod()
5) Client A uses the result of someMethod()
(transaction is still open)
6) Client B starts a transaction
7) Client B asks for ejb1
8) Client B asks for ejb1.collection()
9) Client B asks for ejb1.collection(i).someMethod()
10) Client B uses the result of someMethod()
The server hangs on step 9 and never enters someMethod() (the first line is debug and I never see it). Eventually it tells me that the transaction has timed out with a deadlock exception.
The following comes from the output of a ctrl-break at the point of hanging (someMethod() is getTitle() in this example) :
"HttpRequestHandler-22629000" prio=5 tid=0x434DE690 nid=0xab4 in Object.wait() [4400f000..4400fd8c]
at java.lang.Object.wait(Native Method)
- waiting on <08FC9AC8> (a com.evermind.server.ThreadState)
at com.evermind.server.ejb.AbstractEJBObject.startCall(AbstractEJBObject.java:226)
- locked <08FC9AC8> (a com.evermind.server.ThreadState)
at PersonNamesRemote_EntityBeanWrapper79.getTitle(PersonNamesRemote_EntityBeanWrapper79.java:3227)
at uk.co.corelogic.framework.common.ejb.entity.PeopleEJB.toBean(PeopleEJB.java:1800)
at PeopleRemote_EntityBeanWrapper60.toBean(PeopleRemote_EntityBeanWrapper60.java:1742)
at uk.co.corelogic.framework.common.ejb.session.FrameworkManager.retrieve(FrameworkManager.java:142)
I am using OC4J 9.0.4, Toplink 9.0.3.3. I have Toplink configured to generate BMP Entity beans.
My entity bean deployment descriptor has <reentrant>False</reentrant> but <reentrant>True</reentrant> makes no difference. It also has <trans-attribute>Required</trans-attribute> for everything which should be okay and trying <trans-attribute>Supports</trans-attribute> just causes null pointers to be thrown all over the place.
I will post this message on the OC4J forum too but would appreciate a reply if you have any ideas.
Thanks.
James.

Turn off optimistic locking to prevent ORA-20001

Hi there,
Is it possible to turn-off optimistic locking for tabular forms generated by wizard?
I am using APEX 2.2.0.
I am having ORA-20001 update errors, the only person who is using the form is me. I have read in this forum the solutions some of you have posted to resolve ora-20001 update or delete failures but they all do not work.
I have also read that a turn on and off future will be available in APEX 3.0
Do maybe know how I can turn-off the optimistic locking for my table.
Regards
RobH

I think that the checksum is calculated from the values in the editable fields (hidden or otherwise) when the query is done. If you disable a field later on then it is not included in the checksum for the multi-record update, so you'll get an error when you submit changes.
This isn't anything to do with whether fields are shown or not, but I've just encountered this problem and found there's nothing about it on the forums. Since your problem is also not on the forums I thought it might be the same thing.

Error in Update Process for optimistic locking

Hello,
I tried to create a tabular form according to this How-To:
http://www.oracle.com/technology/products/database/application_express/howtos/tabular_form.html
which worked fine until I tried to implement the optimistic locking.
I use the same update process:
declare
l_cks wwv_flow_global.vc_arr2;
j pls_integer := 1;
begin
-- Get original MD5 checksum
select wwv_flow_item.md5(job,mgr,hiredate,sal,comm,deptno) cks
BULK COLLECT INTO
l_cks
from emp;
-- Compare the original checksum, l_cks,
-- with submitted checksum, htmldb_application.g_fcs.
-- If they are different, raise an error.
for i in 1..l_cks.count
loop
if htmldb_application.g_fcs(i) != l_cks(i) then
rollback;
raise_application_error(
          -20001,
     'Current version of data in database has changed '||
          'since user initiated update process.');
return;
end if;
end loop;
but as soon as I try to apply the changes in the update process I get an error message saying: PLS-00503: RETURN statement required for this return from function
So, if i delete the row with the "return;" statement, I get no error anymore, but when I test the optimistic locking I get an error as soon as I try to update a row in the first place.
What am I doing wrong?
Johnny
P.S. : I am using Apex 1.6

Hi Ant, of course......here is the customized pl/sql block I use:
declare
l_cks wwv_flow_global.vc_arr2;
j pls_integer := 1;
begin
-- Get original MD5 checksum
select wwv_flow_item.md5(partition,desig) cks
BULK COLLECT INTO
l_cks
from UNITS;
-- Compare the original checksum, l_cks,
-- with submitted checksum, htmldb_application.g_fcs.
-- If they are different, raise an error.
for i in 1..l_cks.count
loop
if htmldb_application.g_fcs(i) != l_cks(i) then
rollback;
raise_application_error(-20001,'Current version of data in database has changed ' || 'since user initiated update process.');
-- return;
end if;
end loop;
-- update UNITS
for i in 1..htmldb_application.g_f08.count
loop
if htmldb_application.g_f08(i) is not null then
update UNITS
set report_id = :P2_REPORT_ID,
partition = htmldb_application.g_f10(i),
desig = htmldb_application.g_f11(i)
where unit_id = htmldb_application.g_f08(i);
else
if htmldb_application.g_f10(i) is not null then
insert into UNITS
(report_id,
partition,
desig)
values
(:P2_REPORT_ID,
htmldb_application.g_f10(i),
htmldb_application.g_f11(i));
end if;
end if;
end loop;
end;
Thanks
Johnny

Optimistic locking/ data concurrency and consistency

Hi,
When creating a tabular form using wizard, apex creates its own processes for optimistic locking. But when creating a form on a table, it doesn't create the processes. I suppose I need to create them manually.
Can anybody show me the steps?
Thanks!

Scott,
Thanks once again.
2 things:
My understanding is that I can't change the error message, and that if I want to customize the error message, I need to create my own process for checksum. Is this true? If so, what is the easiest way of doing this?
I realized it returns an error message and the changes the user made gets lost if he went out for lunch and somebody else made an update on that record. What can I do so the user doesn't lose the data?
Thanks,

Optimistic locking and HTML DB checksum calculation

I create a form for fetching and updating row from a database table. I use Automated Row Fetch for fetching row. But for updating row I must use a procedure from a package, not Automatic Row Processing (DML).
And my question is: how I can implement optimistic locking in this way?
Automated Row Fetch already calculated checksum and stored it in p_md5_checksum hidden field, can I get calculated value of checksum from p_md5_checksum?
How I can calculate checksum by myself for compare with value from p_md5_checksum?
What algorithm uses HTML DB for calculate checksum in Automated Row Fetch and Automatic Row Processing (DML) components?

I have read this topic already. It's recommended to build own functionality for calculate checksum, but Automated Row Fetch already calculated checksum and stored it in p_md5_checksum hidden field.
I also created my own function, for example for table dept:
create or replace function BUILD_DEPT_MD5 (
P_DEPTNO in number,
P_DNAME in varchar2 default null,
P_LOC in varchar2 default null,
P_COL_SEP in varchar2 default '|') return varchar2 is
begin
return utl_raw.cast_to_raw(dbms_obfuscation_toolkit.md5(input_string => P_DEPTNO || P_COL_SEP || P_DNAME || P_COL_SEP || P_LOC));
end BUILD_DEPT_MD5;
but checksum values what calculated with this function is not equal with checksum value calculated by Automated Row Fetch.
I shall specify:
I need to use Automated Row Fetch for get row from table.
I can not use Automatic Row Processing (DML) for update row, I need use PL/SQL procedure for this.
I want implement optimistic locking and I want use for this a checksum value, what already calculated by Automated Row Fetch. I need to know how I can get this checksum value and I need to know algorithm, which Automated Row Fetch uses for checksum calculation.

Shuttle item and optimistic lock

Hi everyone,
I need to use a shuttle item to insert/update some data in a table. Because of that, I need to have a pl/sql process that will have the insert or update commands, so no DML allowed in my app page. By doing this, I lose the optimistic lock implemented within the DML process, so I've been searching and reading on how to accomplish this manually.
I followed this post (Re: Optimistic locking on manual non-tabular form among others but it doesn't work properly.
Is there another way to get the optimistic lock manually?
Or better yet, is there a way to update a table from a shuttle item with DML?
btw, i'm using apex 4.1.
Thanks!
Elena.

Hello Elena,
>> tab := apex_util.string_to_table (:p1_multiple_item);
Yes. This is what I meant in parsing the shuttle value.
>> Maybe I'm wrong, but this implies no use of DML, doesn't it?
You are not wrong, although the correct term would be Automatic DML, which is a built-in APEX process (The term DML refers to any insert/update/delete database operation, regardless of APEX).
You didn’t specify if you are familiar with the Optimistic Locking algorithm (which, BTW, pertains only to update data). In any case, my suggestion to you is to use the SQL Workshop to generate a package on your relevant table, and examine the update procedure that was generated. This procedure implements the Optimistic Locking algorithm and can be a great starting point for you to adapt it to your specific needs.
You can generate the package using SQL Workshop ==> Object Browser ==> Create ==> Package ==> Package with methods on database table(s) .
Hope it helps,
Arie.
&diams; Please remember to mark appropriate posts as correct/helpful. For the long run, it will benefit us all.

Pessimistic or optimistic locking

It is highly appreciated someone can provide me with answer to following question.
does iplanet use pessimistic or optimistic locking when ejb associated with transaction accessing the database ?
thanks & regards
Danny

Hi brother
I think that this link can help you
http://download-east.oracle.com/docs/cd/A97688_16/toplink.903/b10064/database.htm#1007986
Good luck

Access to optimistic lock revision number

We have an existing schema that includes a REVISION column. The current JDBC
code base increments the revision number each time an object is updated.
Ideally I would like to use this same field for Kodo's optimistic locking
mechanism and let Kodo manage the field. The problem is that we need
(read-only) access to the revision value for other purposes. Is there a way
to get this value? I'm okay with using a Kodo-specific API.
Thanks,
Tom

Sadly, the mechanism for doing this isn't very well-documented, so here
goes:
import com.solarmetric.kodo.runtime.*;
PersistenceManagerImpl pm = (PersistenceManagerImpl) pman;
StateManagerImpl sm = pm.getState (persistentObject);
Object version = sm.getVersion ();
This object is a Number when used with our JDBC back-end.
-Patrick
On Sat, 02 Aug 2003 09:26:47 -0700, thomasrlandon wrote:
We have an existing schema that includes a REVISION column. The current JDBC
code base increments the revision number each time an object is updated.
Ideally I would like to use this same field for Kodo's optimistic locking
mechanism and let Kodo manage the field. The problem is that we need
(read-only) access to the revision value for other purposes. Is there a way
to get this value? I'm okay with using a Kodo-specific API.
Thanks,
Tom--
Patrick Linskey
SolarMetric Inc.

Query using Optimistic Locking

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