[jira] [Created] (MESOS-1165) Retry required when recovering an empty log

["Jie Yu (JIRA)" <ji...@apache.org>]

Jie Yu created MESOS-1165:
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             Summary: Retry required when recovering an empty log
                 Key: MESOS-1165
                 URL: https://issues.apache.org/jira/browse/MESOS-1165
             Project: Mesos
          Issue Type: Bug
            Reporter: Jie Yu
            Priority: Minor


Reported by [~benjaminhindman]. It's fairly non-intuitive that a 'fill' retry is required when recovering an empty log. Moreover, since retry is done via a 'delay' it means that you can't pause the clock before calling Log::Writer::start! The following tests show the multiple calls and at one point I added comments to explain the very esoteric reasoning here. Here are the sequence of events:

First a replica is recovered with nothing but 0 is always a hole:

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Replica recovered with log positions 0 -> 0 with 1 holes and 0 unlearned
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At this point the replica assumes it was promised to a coordinator with proposal 0 (that's the default metadata). Then an implicit promise request is made with proposal 1.

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Replica received implicit promise request with proposal 1 
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Then the coordinator (via FillProcess) tries to fill the hole (position 0) explicitly:

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Coordinator attemping to fill missing position 
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And the replica receives the request:

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Replica received explicit promise request for position 0 with proposal 1
----

But the filling must be retried because the 0th position is implicitly promised to proposer 1 (the same coordinator!) but the replica won't allow it (because it might not be safe) so the FillProcess now tries with proposal number 2 (after the delay). While correct, this seems unfortunate (and not intuitive).



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