[infinispan-issues] [JBoss JIRA] Created: (ISPN-799) JoinTask as it invalidates L1 entries should be given precedence in acquiring locks

[Vladimir Blagojevic (JIRA)]

JoinTask as it invalidates L1 entries should be given precedence in acquiring locks 
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                 Key: ISPN-799
                 URL: https://jira.jboss.org/browse/ISPN-799
             Project: Infinispan
          Issue Type: Bug
          Components: Locking and Concurrency
    Affects Versions: 4.2.0.CR1
            Reporter: Vladimir Blagojevic
            Assignee: Manik Surtani
             Fix For: 4.2.0.Final, 5.0.0.Final


The SingleJoinTest transaction test failure itself is intermittent due to the way addresses are organised in the hash wheel, so you are correct that it is a timing issue.  Anyway, it still is a very real problem.  Just to re-iterate and to make sure we are talking about the same thing:

1.  View is {A, B, C}
2.  K is mapped to {A, B}
3.  A tx starts to update K, and is prepared.  Locks now held for K on {A, B}
4.  D joins.  D is placed on the hash wheel between A and B.  So the new view is {A, D, B, C}
5.  As per the test (artificial, I know, but could still happen), the tx waits for a long time before committing.  In the case of the test, artificially waits until D has finished joining before committing, by use of a latch.
6.  D never joins as even though it receives the prepare for the tx and could potentially commit itself (as a new owner), it fails as it is unable to invalidate K on B.

There are a few solutions here:

1)  This is pretty easy to detect.  Attempt to acquire the lock with a smaller lock acquisition timeout and if the transaction is still stuck, abort the transaction and proceed with the join.
2)  If the blocking node is *not* the transaction originator (as in this case: the tx was started on A), then just force lock removal and tx rollback on B *only*.  Let the tx complete on A, since the new joiner will receive the transactional event and will be able to apply it as a new owner.

My vote is to go for solution 1 - a bit more crude, but 2 would be very complex to implement.  And even then, would only solve for  the invalidation being blocked on a node that did not originate the transaction.  E.g., the tx originated on A but the lock issue was on B.  If, however, the tx originated on B, *and* B no longer owns the entry in question, then 2 is no longer a solution and the only solution would be 1.


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