[kudu-CR] KUDU-2780: create thread for auto-rebalancing

["Hannah Nguyen (Code Review)" <ge...@cloudera.org>]

Hello Tidy Bot, Alexey Serbin, Kudu Jenkins, Andrew Wong, 

I'd like you to reexamine a change. Please visit

    http://gerrit.cloudera.org:8080/14177

to look at the new patch set (#6).

Change subject: KUDU-2780: create thread for auto-rebalancing
......................................................................

KUDU-2780: create thread for auto-rebalancing

The auto-rebalancer thread is a background task of the master's
catalog manager. Each loop iteration, the thread collects information
on tservers, tables, and tablets, in order to determine the best
rebalancing replica moves for the cluster. The loop will continue,
determining and executing a certain number of moves per iteration.
The number of replica moves per server, per loop iteration, is controlled
by a flag.

If the cluster has placement policy violations, the thread will schedule
and execute replica moves to reinstate the policy. Otherwise, the thread
will perform inter-location(cross-location), then intra-location(by table,
then by tserver) rebalancing.

If the thread finds that the cluster is already balanced, the current
rebalancing cycle completes. The thread will sleep for a time interval,
controlled by a flag.

By default, auto-rebalancing is disabled. This can be changed by a flag
in the catalog manager.

Change-Id: Ifca25d1063c07047cf2123e6792b3c7395be20e4
---
M src/kudu/master/CMakeLists.txt
A src/kudu/master/auto_rebalancer-test.cc
A src/kudu/master/auto_rebalancer.cc
A src/kudu/master/auto_rebalancer.h
M src/kudu/master/catalog_manager.cc
M src/kudu/master/catalog_manager.h
M src/kudu/master/ts_descriptor.cc
M src/kudu/master/ts_descriptor.h
M src/kudu/rebalance/rebalancer.cc
M src/kudu/rebalance/rebalancer.h
M src/kudu/tools/rebalancer_tool.cc
11 files changed, 1,308 insertions(+), 109 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/77/14177/6
-- 
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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Ifca25d1063c07047cf2123e6792b3c7395be20e4
Gerrit-Change-Number: 14177
Gerrit-PatchSet: 6
Gerrit-Owner: Hannah Nguyen <ha...@cloudera.com>
Gerrit-Reviewer: Alexey Serbin <as...@cloudera.com>
Gerrit-Reviewer: Andrew Wong <aw...@cloudera.com>
Gerrit-Reviewer: Hannah Nguyen <ha...@cloudera.com>
Gerrit-Reviewer: Kudu Jenkins (120)
Gerrit-Reviewer: Tidy Bot (241)