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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