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https://issues.apache.org/jira/browse/HBASE-5572?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13228476#comment-13228476
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nkeywal commented on HBASE-5572:
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Yes. I've done 3 modifications in the code, two like for like (hopefully!) and
one with a different behavior. I:
- removed the variable named cleanSetOfActiveMaster, replaced by "return true"
or "return false".
- replaced the recursive call by a while(true) loop.
- implicitly (it's hidden because there is no recursive call anymore) changed
the function behavior: we now return the final result. For this reason the
function behaves differently (we return true instead of false), but it's more
on line with the method contract. This change breaks the
testMasterZKSessionRecoveryFailure, because it does not fail anymore.
TestMasterZKSessionRecovery#testMasterZKSessionRecoveryFailure was testing
explicitly the behavior with both SessionExpired AND master with same host &
port. I removed it, but I can move it to TestZooKeeper (to save a cluster
start/stop) and reverse the assertion in the test (now it does not fail).
> KeeperException.SessionExpiredException management could be improved in Master
> ------------------------------------------------------------------------------
>
> Key: HBASE-5572
> URL: https://issues.apache.org/jira/browse/HBASE-5572
> Project: HBase
> Issue Type: Improvement
> Components: master
> Affects Versions: 0.96.0
> Reporter: nkeywal
> Assignee: nkeywal
> Priority: Minor
> Attachments: 5572.v1.patch
>
>
> Synthesis:
> 1) TestMasterZKSessionRecovery distinguish two cases on
> SessionExpiredException. One is explicitly not managed. However, is seems
> that there is no reason for this.
> 2) The issue lies in ActiveMasterManager#blockUntilBecomingActiveMaster, a
> quite complex function, with a useless recursive call.
> 3) TestMasterZKSessionRecovery#testMasterZKSessionRecoverySuccess is
> equivalent to TestZooKeeper#testMasterSessionExpired
> 4) TestMasterZKSessionRecovery#testMasterZKSessionRecoveryFailure can be
> removed if we merge the two cases mentioned above.
> Changes are:
> 2) Changing ActiveMasterManager#blockUntilBecomingActiveMaster to have a
> single case and remove recursion
> 1) Removing TestMasterZKSessionRecovery
> Detailed justification:
> testMasterZKSessionRecoveryFailure says:
> {noformat}
> /**
> * Negative test of master recovery from zk session expiry.
> *
> * Starts with one master. Fakes the master zk session expired.
> * Ensures the master cannot recover the expired zk session since
> * the master zk node is still there.
> */
> public void testMasterZKSessionRecoveryFailure() throws Exception {
> MiniHBaseCluster cluster = TEST_UTIL.getHBaseCluster();
> HMaster m = cluster.getMaster();
> m.abort("Test recovery from zk session expired",
> new KeeperException.SessionExpiredException());
> assertTrue(m.isStopped());
> }
> {noformat}
> This tests works, i.e. the assertion is always verified.
> But do we really want this behavior?
> When looking at the code, we see that this what's happening is strange:
> - HMaster#abort calls Master#abortNow. If HMaster#abortNow returns false
> HMaster#abort stops the master.
> - HMaster#abortNow checks the exception type. As it's a
> SessionExpiredException it will try to recover, calling
> HMaster#tryRecoveringExpiredZKSession. If it cannot, it will return false
> (and that will make HMaster#abort stopping the master)
> - HMaster#tryRecoveringExpiredZKSession recreates a ZooKeeperConnection and
> then try to become the active master. If it cannot, it will return false (and
> that will make HMaster#abort stopping the master).
> - HMaster#becomeActiveMaster returns the result of
> ActiveMasterManager#blockUntilBecomingActiveMaster.
> blockUntilBecomingActiveMaster says it will return false if there is any
> error preventing it to become the active master.
> - ActiveMasterManager#blockUntilBecomingActiveMaster reads ZK for the master
> address. If it's the same port & host, it deletes the nodes, that will start
> a recursive call to blockUntilBecomingActiveMaster. This second call succeeds
> (we became the active master) and return true. This result is ignored by the
> first blockUntilBecomingActiveMaster: it return false (even if we actually
> became the active master), hence the whole suite call returns false and
> HMaster#abort stops the master.
> In other words, the comment says "Ensures the master cannot recover the
> expired zk session since the master zk node is still there." but we're
> actually doing a check just for this and deleting the node. If we were not
> ignoring the result, we would return "true", so we would not stop the master,
> so the test would fail.
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