handling concurrency right why am i wrong?

hi group,

i have the following problem.
i have a simple updateable view V with a status field S.

nowadays i have two clients that try to consume data out of this view V if S = 'TOBEPROCESSED'
the two clients are jdbc clients and they try the following every 30 seconds.
each clients tries to ----------------- update V set S ='$MYCLIENTID' where S = 'TOBEPROCESSED'
in this way i try to reserve the current available data TOBEPROCESSED for one client and then process it.

when i do this i sometimes (if they overlap) get the following exception:


Stacktrace: java.sql.SQLException: ERROR: deadlock detected
        at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:1365)
        at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1160)
        at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:172)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:387)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:328)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:319)
        at ComponentsJcdIn.jcdReader.handleConnection(ComponentsJcdIn.jcdReader:303)
        at ComponentsJcdIn.jcdReader.start(ComponentsJcdIn.jcdReader:108)
        at prjGwiJdbc1mGenericStagingMulti.csvcReader.jcdReader_Runtime_Handler.handleRequest(prjGwiJdbc1mGenericStagingMulti.csvcReader.jcdReader_Runtime_Handler:381)
        at sun.reflect.GeneratedMethodAccessor593.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at com.sun.enterprise.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1067)
        at com.sun.enterprise.security.SecurityUtil.invoke(SecurityUtil.java:176)
        at com.sun.ejb.containers.BaseContainer.invokeTargetBeanMethod(BaseContainer.java:2899)
        at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:3990)
        at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:197)
        at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:134)
        at $Proxy443.handleRequest(Unknown Source)

what exactly does that mean?
is my tactic wrong?
in oracle this works just fine.

regards chris

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Christian Brennsteiner
Salzburg / Austria / Europe