[jira] [Created] (KAFKA-13073) Simulation test fails due to inconsistency in MockLog's implementation

["Jose Armando Garcia Sancio (Jira)" <ji...@apache.org>]

Jose Armando Garcia Sancio created KAFKA-13073:
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             Summary: Simulation test fails due to inconsistency in MockLog's implementation
                 Key: KAFKA-13073
                 URL: https://issues.apache.org/jira/browse/KAFKA-13073
             Project: Kafka
          Issue Type: Bug
          Components: controller, replication
    Affects Versions: 3.0.0
            Reporter: Jose Armando Garcia Sancio
            Assignee: Jose Armando Garcia Sancio
             Fix For: 3.0.0


We are getting the following error on trunk
{code:java}
RaftEventSimulationTest > canRecoverAfterAllNodesKilled STANDARD_OUT
    timestamp = 2021-07-12T16:26:55.663, RaftEventSimulationTest:canRecoverAfterAllNodesKilled =
      java.lang.RuntimeException:
        Uncaught exception during poll of node 1                                  |-------------------jqwik-------------------
    tries = 25                    | # of calls to property
    checks = 25                   | # of not rejected calls
    generation = RANDOMIZED       | parameters are randomly generated
    after-failure = PREVIOUS_SEED | use the previous seed
    when-fixed-seed = ALLOW       | fixing the random seed is allowed
    edge-cases#mode = MIXIN       | edge cases are mixed in
    edge-cases#total = 108        | # of all combined edge cases
    edge-cases#tried = 4          | # of edge cases tried in current run
    seed = 8079861963960994566    | random seed to reproduce generated values    Sample
    ------
      arg0: 4002
      arg1: 2
      arg2: 4{code}
I think there are a couple of issues here:
 # The {{ListenerContext}} for {{KafkaRaftClient}} uses the value returned by {{ReplicatedLog::startOffset()}} to determined the log start and when to load a snapshot while the {{MockLog}} implementation uses {{logStartOffset}} which could be a different value.
 # {{MockLog}} doesn't implement {{ReplicatedLog::maybeClean}} so the log start offset is always 0.
 # The snapshot id validation for {{MockLog}} and {{KafkaMetadataLog}}'s {{createNewSnapshot}} throws an exception when the snapshot id is less than the log start offset.

Solutions:

Fix the error quoted above we only need to fix bullet point 3. but I think we should fix all of the issues enumerated in this Jira.

For 1. we should change the {{MockLog}} implementation so that it uses {{startOffset}} both externally and internally.

For 2. I will file another issue to track this implementation.

For 3. I think this validation is too strict. I think it is safe to simply ignore any attempt by the state machine to create an snapshot with an id less that the log start offset. We should return a {{Optional.empty()}}when the snapshot id is less than the log start offset. This tells the user that it doesn't need to generate a snapshot for that offset. 



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