Merge failure when dead instances remain in view

I've hit this testing my JGRP-1485 fix, but I think it's a logically independent issue.

So, I've reached a point where:

• A, B and C all have view {C,A,B}
• D has view {B', D', D, A', C}

  , in which B', D' and A' are all dead instances

As in JGRP-1485, an optimal fix would surely be to allow D to recover all by itself, but it's not clear to me how to do that. However, my expectation was that a merge should sort things out; and I think that if it did then that ought to be good enough.

But what's actually happening is this:

• C becomes merge leader
• determines that merge participants are C, D', D, A'
• sends MERGE_REQ to those members
• the MERGE_REQ to D' reaches D (and that to A' reaches A)
• D sends a positive response for the MERGE_REQ that was meant for it, but after 2.5 seconds also sends a negative response to the MERGE_REQ meant for D'. (I think that the negative response is because it can't fetch the digest from D')
• likewise A sends a negative response to the MERGE_REQ meant for A'

So what C sees is:

• good responses from C and D, followed by merge_rejected responses from A and D
• so it removes A' and D' from the merge (it didn't get responses from them)
• then it removes D from the merge (because the most recent response from D said merge_rejected)
• so it is left only with itself, and comes up with a consolidated view that is identical to its original view

in short: the merge doesn't do anything useful after all.

I think that the key here is the confusion between D and D'. Possibly the fix is as simple as: ignore MERGE_REQs where the destination address on the message is not the local address.

I'll try this out and, if it looks good, submit a pull request.