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https://issues.apache.org/jira/browse/HBASE-16853?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15580931#comment-15580931
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Heng Chen commented on HBASE-16853:
-----------------------------------
+1
> Regions are assigned to Region Servers in /hbase/draining after HBase Master
> failover
> -------------------------------------------------------------------------------------
>
> Key: HBASE-16853
> URL: https://issues.apache.org/jira/browse/HBASE-16853
> Project: HBase
> Issue Type: Bug
> Components: Balancer, Region Assignment
> Affects Versions: 2.0.0, 1.3.0
> Reporter: David Pope
> Assignee: David Pope
> Fix For: 2.0.0, 1.3.0, 1.4.0
>
> Attachments: 16853.v2.txt, HBASE-16853.branch-1.3-v1.patch,
> HBASE-16853.branch-1.3-v2.patch
>
>
> h2. Problem
> If there are Region Servers registered as "draining", they will continue to
> have "draining" znodes after a HMaster failover; however, the balancer will
> assign regions to them.
> h2. How to reproduce (on hbase master):
> # Add regionserver to /hbase/draining: {{bin/hbase-jruby
> bin/draining_servers.rb add server1:16205}}
> # Unload the regionserver: {{bin/hbase-jruby bin/region_mover.rb unload
> server1:16205}}
> # Kill the Active HMaster and failover to the Backup HMaster
> # Run the balancer: {{hbase shell <<< "balancer"}}
> # Notice regions get assigned on new Active Master to Region Servers in
> /hbase/draining
> h2. Root Cause
> The Backup HMaster initializes the {{DrainingServerTracker}} before the
> Region Servers are registered as "online" with the {{ServerManager}}. As a
> result, the {{ServerManager.drainingServers}} isn't populated with existing
> Region Servers in draining when we have an HMaster failover.
> E.g.,
> # We have a region server in draining: {{server1,16205,1000}}
> # The {{RegionServerTracker}} starts up and adds a ZK watcher on the Znode
> for this RegionServer: {{/hbase/rs/server1,16205,1000}}
> # The {{DrainingServerTracker}} starts and processes each Znode under
> {{/hbase/draining}}, but the Region Server isn't registered as "online" so it
> isn't added to the {{ServerManager.drainingServers}} list.
> # The Region Server is added to the {{DrainingServerTracker.drainingServers}}
> list.
> # The Region Server's Znode watcher is triggered and the ZK watcher is
> restarted.
> # The Region Server is registered with {{ServerManager}} as "online".
> *END STATE:* The Region Server has a Znode in {{/hbase/draining}}, but it is
> registered as "online" and the Balancer will start assigning regions to it.
> {code}
> $ bin/hbase-jruby bin/draining_servers.rb list
> [1] server1,16205,1000
> $ grep server1,16205,1000 logs/master-server1.log
> 2016-10-14 16:02:47,713 DEBUG [server1:16001.activeMasterManager]
> zookeeper.ZKUtil: master:16001-0x157c56adc810014, quorum=localhost:2181,
> baseZNode=/hbase Set watcher on existing znode=/hbase/rs/server1,16205,1000
> [2] 2016-10-14 16:02:47,722 DEBUG [server1:16001.activeMasterManager]
> zookeeper.RegionServerTracker: Added tracking of RS
> /hbase/rs/server1,16205,1000
> 2016-10-14 16:02:47,730 DEBUG [server1:16001.activeMasterManager]
> zookeeper.ZKUtil: master:16001-0x157c56adc810014, quorum=localhost:2181,
> baseZNode=/hbase Set watcher on existing
> znode=/hbase/draining/server1,16205,1000
> [3] 2016-10-14 16:02:47,731 WARN [server1:16001.activeMasterManager]
> master.ServerManager: Server server1,16205,1000 is not currently online.
> Ignoring request to add it to draining list.
> [4] 2016-10-14 16:02:47,731 INFO [server1:16001.activeMasterManager]
> zookeeper.DrainingServerTracker: Draining RS node created, adding to list
> [server1,16205,1000]
> 2016-10-14 16:02:47,971 DEBUG [main-EventThread] zookeeper.ZKUtil:
> master:16001-0x157c56adc810014, quorum=localhost:2181, baseZNode=/hbase Set
> watcher on existing
> znode=/hbase/rs/dev6918.prn2.facebook.com,16205,1476486047114
> [5] 2016-10-14 16:02:47,976 DEBUG [main-EventThread]
> zookeeper.RegionServerTracker: Added tracking of RS
> /hbase/rs/server1,16205,1000
> [6] 2016-10-14 16:02:52,084 INFO
> [RpcServer.FifoWFPBQ.default.handler=29,queue=2,port=16001]
> master.ServerManager: Registering server=server1,16205,1000
> {code}
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