[jbossts-issues] [JBoss JIRA] (JBTM-3020) Add ability for resources to indicate XA_RDONLY on end

[David Lloyd (JIRA)]

David Lloyd created JBTM-3020:
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             Summary: Add ability for resources to indicate XA_RDONLY on end
                 Key: JBTM-3020
                 URL: https://issues.jboss.org/browse/JBTM-3020
             Project: JBoss Transaction Manager
          Issue Type: Feature Request
            Reporter: David Lloyd


As discussed in WFLY-10258 and https://developer.jboss.org/message/982097, this request is to add the ability for an XAResource to indicate (on end) that it has no committable work, which would act as a hint to order that XAResource at an earlier point of prepare processing, which will in turn increase the chances of a 1PC optimization occurring.

As expressed in the forum thread, the mechanism should not interfere with compatibility.  One possible way to do this would be to introduce an enhanced subinterface of XAResource which includes a method like this:

{code:java}
    int endWithResult(Xid xid, int flags) throws XAException;
{code}

The method behaves semantically identically to {{XAResource#end}} , except it would be allowed to return {{XA_RDONLY}} or {{XA_OK}}.  A value of {{XA_RDONLY}} would indicate that the resource expects to return {{XA_RDONLY}} in response to a {{prepare}} call, whereas a value of {{XA_OK}} indicates that the resource's future {{prepare}} result cannot yet be decided or will be {{XA_OK}}.  An invalid result should probably behave equivalently to an {{XAException}} being thrown by the {{end}} method.  {{XAER_RMERR}} seems like a reasonable error code for this case.

Since it's a subinterface of {{XAResource}}, it could also define the following default method:

{code:java}
    default void end(Xid xid, int flags) throws XAException {
        endWithResult(xid, flags);
    }
{code}

This method would not need to be called by the TM, but would correctly satisfy the {{XAResource}} contract without requiring the user to implement the redundant method.



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