Move report of split to master OFF the heartbeat channel
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Key: HBASE-3559
URL: https://issues.apache.org/jira/browse/HBASE-3559
Project: HBase
Issue Type: Task
Reporter: stack
The heartbeat in hbase is about to go away. See hbase-1502. This issue is
about moving the report of a split region off the heartbeat channel. This work
needs to be done before I can finish up hbase-1502.
Here is a provisional 'design' for how report of split to master will now work.
Instead of riding a split message on the regionserver to master heartbeat, the
regionserver will put up a znode under (the badly named) 'unassigned'
directory; i.e. the regionserver will put the region into 'transition' (RIT).
Usually the master does all RIT machinations. Splits will be an exception.
The regionserver will move the znode through two states: SPLITTING and SPLIT.
The master will clean up the SPLIT znode on receipt of child changed callback.
There will be no extra data in the SPLITTING znode beyond the SPLITTING state
name. The SPLIT znode will contain the name of the split daughters.
Any region in RIT will block the balancer running. This could be an issue if
lots of splits going on across a cluster.
Master will need to handle new SPLIT and SPLITTING states and that another may
have already written the RIT (unit tests).
As before, regionserver figures region to split and runs
CompactSplitThread#split. As before, this invokes SplitTransaction with its
prepare, execute and when necessary rollback phase. Into the execute we'll add
the setting of SPLITTING znode into RIT. The execution will end with setting
the SPLIT znode state. Master will read and clear the SPLIT state when done.
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