[jira] [Created] (HELIX-276) Allow FULL_AUTO mode to favor some transitions

["Matthieu Morel (JIRA)" <ji...@apache.org>]

Matthieu Morel created HELIX-276:
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             Summary: Allow FULL_AUTO mode to favor some transitions
                 Key: HELIX-276
                 URL: https://issues.apache.org/jira/browse/HELIX-276
             Project: Apache Helix
          Issue Type: Improvement
            Reporter: Matthieu Morel


In FULL_AUTO mode, helix computes both partitioning and states.

Currently, in a master-replica model, when rebalancing due to a failure of the master node, Helix does not promote an existing replica to master, but instead assigns a new master (I.e. offline -> replica -> master).

The current algorithm optimizes for minimal partition movement and even distribution of state. However, it should also take into account the priorities between states, or provide a way to customize it. For instance, when it is more costly (number of transitions, priorities) to perform offline -> master than replica -> master, the algorithm could favor replica -> master transitions.

One application would be for quick failover : mater ops are logged to a journal, a replica builds its state by tailing the journal, and upon failure of the master, recovery is fast since only a few operations may have to be played to reach the latest state of the master. If a new node is assigned master role from scratch, the whole journal must be replayed.

More context in this thread:

http://markmail.org/message/inq6tnlnk5ckscwr



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