KeeperException.SessionExpiredException management could be improved in Master
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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
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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