Deferred Enlistment

 

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Overview

In the WAS environment, deferred enlistment is a term used to refer to the technique of waiting until a connection is first used to enlist it in its unit of work (UOW) scope.

In one example, the technique works like this: a component calls getConnection() from within a global transaction, and at some point later in time, the component uses the connection. The call that uses the connection is intercepted, and the XA resource for that connection is enlisted with the transaction service (which in turn calls XAResource.start()). Next, the actual call is sent to the resource manager.

In contrast, if a component gets a connection within a global transaction without deferred enlistment, then the connection is enlisted in the transaction and has all the overhead associated with that transaction. For XA connections, this includes the two phase commit (2PC) protocol to the resource manager. Deferred enlistment offers better performance in the case where a connection is obtained, but not used within the UOW scope. This saves all the overhead of participating in the UOW when it is not needed.

The WAS relational resource adapter automatically supports deferred enlistment without any additional configuration needed.

 

Lazy Transaction Enlistment Optimization

The JCA V1.5 specification calls the deferred enlistment technique lazy transaction enlistment optimization. This support comes through a marker interface (LazyEnlistableManagedConnection) and a new method on the connection manager (LazyEnlistableConnectionManager())

package javax.resource.spi;
import javax.resource.ResourceException;
import javax.transaction.xa.Xid;

interface LazyEnlistableConnectionManager 
{ 
    // application server
    void lazyEnlist(ManagedConnection) throws ResourceException;
}

interface LazyEnlistableManagedConnection 
{ 
    // resource adapter
}

A resource adapter is not required to support this functionality. Check with the resource adapter provider to know if the resource adapter provides this functionality.

 

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