David Pope created HBASE-16853:
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Summary: 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: Region Assignment
Affects Versions: 2.0.0, 1.3.0
Reporter: David Pope
Assignee: David Pope
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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