Joshua Humphries created SOLR-10276:
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Summary: Update ZK leader election so that leader notices if its
leadership is revoked
Key: SOLR-10276
URL: https://issues.apache.org/jira/browse/SOLR-10276
Project: Solr
Issue Type: Improvement
Security Level: Public (Default Security Level. Issues are Public)
Components: SolrCloud
Affects Versions: 5.5.3
Reporter: Joshua Humphries
Priority: Minor
When we have an issue with a solr node, it would be nice to revoke its
leadership of one or more shard or to revoke its role as overseer without
actually restarting the node. (Restarting the node tends to spam the overseer
queue since we have a very large number of cores per node.)
Operationally, it would be nice if one could just delete the leader's election
node (e.g. its ephemeral sequential node that indicates it as current leader)
and to have it notice the change and stop behaving as leader.
Currently, once a node becomes leader, it isn't watching ZK for any changes
that could revoke its leadership. I am proposing that, upon being elected
leader, it use a ZK watch to monitor its own election node. If its own election
node is deleted, it then relinquishes leadership (e.g. calls
ElectionContext#cancelElection() and then re-joins the election).
I have a patch with tests that I can contribute.
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