最近生产环境hbase集群出现停掉集群之后hmaster无法启动现象，master日志报异常：Timedout 300000ms waiting for namespace table to be assigned，导致整个集群起不来。
2016-12-12 18:04:12,243 FATAL [adfnn2:16020.activeMasterManager] master.HMaster: Failed to become active master
java.io.IOException: Timedout 300000ms waiting for namespace table to be assigned
at org.apache.hadoop.hbase.master.TableNamespaceManager.start(TableNamespaceManager.java:98)
at org.apache.hadoop.hbase.master.HMaster.initNamespace(HMaster.java:868)
at org.apache.hadoop.hbase.master.HMaster.finishActiveMasterInitialization(HMaster.java:719)
at org.apache.hadoop.hbase.master.HMaster.access$500(HMaster.java:165)
at org.apache.hadoop.hbase.master.HMaster$1.run(HMaster.java:1425)
首先怀疑regionserver加载namespace region出现异常，导致namespace表加载失败，但是查看所有regionserver日志，没有异常出现。
那么就分析master日志，更改log4j日志为debug，看看能不能找到关键信息，有没可能是region太多，在五分钟之内没有分配完导致namespace表还没加载，看下面的region分配日志，2016-12-12 17:59:36,571之后再也没有region分配日志，说明所有region已经分配完成，再看看上面异常日志，2016-12-12 18:04:12,243报的异常，17:59:36,571至18:04:12,243期间没有region分配，的确说明region已经全部分配完成。
2016-12-12 17:59:36,492 INFO [AM.ZK.Worker-pool2-t8] master.RegionStates: Onlined 11d3cd3c7166f4f81286d9d7ac854421 on adfdn14,16020,1481536735081
2016-12-12 17:59:36,492 INFO [AM.ZK.Worker-pool2-t8] master.RegionStates: Offlined 11d3cd3c7166f4f81286d9d7ac854421 from adfdn20,16020,1481525544193
2016-12-12 17:59:36,532 DEBUG [main-EventThread] zookeeper.ZooKeeperWatcher: master:16020-0x258dd1d8ea30c00, quorum=adfdn02:2181,adfdn04:2181,adfdn03:2181, baseZNode=/hbase Received ZooKeeper Event, type=NodeDataChanged, state=SyncConnected, path=/hbase/region-in-transition/2df9448afa2470e488b92feb50f65e20
2016-12-12 17:59:36,533 DEBUG [AM.ZK.Worker-pool2-t2] master.AssignmentManager: Handling RS_ZK_REGION_OPENED, server=adfdn14,16020,1481536735081, region=2df9448afa2470e488b92feb50f65e20, current_state={2df9448afa2470e488b92feb50f65e20 state=OPENING, ts=1481536776150, server=adfdn14,16020,1481536735081}
2016-12-12 17:59:36,533 INFO [AM.ZK.Worker-pool2-t2] master.RegionStates: Transition {2df9448afa2470e488b92feb50f65e20 state=OPENING, ts=1481536776150, server=adfdn14,16020,1481536735081} to {2df9448afa2470e488b92feb50f65e20 state=OPEN, ts=1481536776533, server=adfdn14,16020,1481536735081}
2016-12-12 17:59:36,533 DEBUG [AM.ZK.Worker-pool2-t2] coordination.ZkOpenRegionCoordination: Handling OPENED of 2df9448afa2470e488b92feb50f65e20 from adfnn2,16020,1481536732124; deleting unassigned node
2016-12-12 17:59:36,535 DEBUG [main-EventThread] zookeeper.ZooKeeperWatcher: master:16020-0x258dd1d8ea30c00, quorum=adfdn02:2181,adfdn04:2181,adfdn03:2181, baseZNode=/hbase Received ZooKeeper Event, type=NodeDeleted, state=SyncConnected, path=/hbase/region-in-transition/2df9448afa2470e488b92feb50f65e20
2016-12-12 17:59:36,535 DEBUG [main-EventThread] zookeeper.ZooKeeperWatcher: master:16020-0x258dd1d8ea30c00, quorum=adfdn02:2181,adfdn04:2181,adfdn03:2181, baseZNode=/hbase Received ZooKeeper Event, type=NodeChildrenChanged, state=SyncConnected, path=/hbase/region-in-transition
2016-12-12 17:59:36,535 DEBUG [AM.ZK.Worker-pool2-t2] zookeeper.ZKAssign: master:16020-0x258dd1d8ea30c00, quorum=adfdn02:2181,adfdn04:2181,adfdn03:2181, baseZNode=/hbase Deleted unassigned node 2df9448afa2470e488b92feb50f65e20 in expected state RS_ZK_REGION_OPENED
2016-12-12 17:59:36,536 DEBUG [AM.ZK.Worker-pool2-t2] master.AssignmentManager: Znode THB_GPRS_FLOW_201610,b2bb,1476080598693.2df9448afa2470e488b92feb50f65e20. deleted, state: {2df9448afa2470e488b92feb50f65e20 state=OPEN, ts=1481536776533, server=adfdn14,16020,1481536735081}
2016-12-12 17:59:36,536 INFO [AM.ZK.Worker-pool2-t2] master.RegionStates: Onlined 2df9448afa2470e488b92feb50f65e20 on adfdn14,16020,1481536735081
2016-12-12 17:59:36,536 INFO [AM.ZK.Worker-pool2-t2] master.RegionStates: Offlined 2df9448afa2470e488b92feb50f65e20 from adfdn20,16020,1481525544193
2016-12-12 17:59:36,568 DEBUG [main-EventThread] zookeeper.ZooKeeperWatcher: master:16020-0x258dd1d8ea30c00, quorum=adfdn02:2181,adfdn04:2181,adfdn03:2181, baseZNode=/hbase Received ZooKeeper Event, type=NodeDataChanged, state=SyncConnected, path=/hbase/region-in-transition/07d3e0689ce6b0f62ad9cf7084d82588
2016-12-12 17:59:36,569 DEBUG [AM.ZK.Worker-pool2-t5] master.AssignmentManager: Handling RS_ZK_REGION_OPENED, server=adfdn14,16020,1481536735081, region=07d3e0689ce6b0f62ad9cf7084d82588, current_state={07d3e0689ce6b0f62ad9cf7084d82588 state=OPENING, ts=1481536776166, server=adfdn14,16020,1481536735081}
2016-12-12 17:59:36,569 INFO [AM.ZK.Worker-pool2-t5] master.RegionStates: Transition {07d3e0689ce6b0f62ad9cf7084d82588 state=OPENING, ts=1481536776166, server=adfdn14,16020,1481536735081} to {07d3e0689ce6b0f62ad9cf7084d82588 state=OPEN, ts=1481536776569, server=adfdn14,16020,1481536735081}
2016-12-12 17:59:36,569 DEBUG [AM.ZK.Worker-pool2-t5] coordination.ZkOpenRegionCoordination: Handling OPENED of 07d3e0689ce6b0f62ad9cf7084d82588 from adfnn2,16020,1481536732124; deleting unassigned node
2016-12-12 17:59:36,571 DEBUG [main-EventThread] zookeeper.ZooKeeperWatcher: master:16020-0x258dd1d8ea30c00, quorum=adfdn02:2181,adfdn04:2181,adfdn03:2181, baseZNode=/hbase Received ZooKeeper Event, type=NodeDeleted, state=SyncConnected, path=/hbase/region-in-transition/07d3e0689ce6b0f62ad9cf7084d82588
2016-12-12 17:59:36,571 DEBUG [main-EventThread] zookeeper.ZooKeeperWatcher: master:16020-0x258dd1d8ea30c00, quorum=adfdn02:2181,adfdn04:2181,adfdn03:2181, baseZNode=/hbase Received ZooKeeper Event, type=NodeChildrenChanged, state=SyncConnected, path=/hbase/region-in-transition
2016-12-12 17:59:36,571 DEBUG [AM.ZK.Worker-pool2-t5] zookeeper.ZKAssign: master:16020-0x258dd1d8ea30c00, quorum=adfdn02:2181,adfdn04:2181,adfdn03:2181, baseZNode=/hbase Deleted unassigned node 07d3e0689ce6b0f62ad9cf7084d82588 in expected state RS_ZK_REGION_OPENED
2016-12-12 17:59:36,571 DEBUG [AM.ZK.Worker-pool2-t5] master.AssignmentManager: Znode THB_GPRS_WAP_201612,b24e,1480493880237.07d3e0689ce6b0f62ad9cf7084d82588. deleted, state: {07d3e0689ce6b0f62ad9cf7084d82588 state=OPEN, ts=1481536776569, server=adfdn14,16020,1481536735081}
2016-12-12 17:59:36,571 INFO [AM.ZK.Worker-pool2-t5] master.RegionStates: Onlined 07d3e0689ce6b0f62ad9cf7084d82588 on adfdn14,16020,1481536735081
2016-12-12 17:59:36,571 INFO [AM.ZK.Worker-pool2-t5] master.RegionStates: Offlined 07d3e0689ce6b0f62ad9cf7084d82588 from adfdn20,16020,1481525544193
2016-12-12 17:59:55,765 DEBUG [adfnn2:16020.archivedHFileCleaner] cleaner.CleanerChore: Removing: hdfs://qhcm/hbase/archive/data/default/THB_USER_FLOW_201610/00afb5e7f30354607a5433ce66c7ea94/F/93527541ef45469f98bb728470d7dc86 from archive
2016-12-12 17:59:55,831 DEBUG [adfnn2:16020.archivedHFileCleaner] cleaner.CleanerChore: Removing: hdfs://qhcm/hbase/archive/data/default/THB_USER_FLOW_201610/00afb5e7f30354607a5433ce66c7ea94/recovered.edits/8509.seqid from archive
2016-12-12 17:59:55,853 DEBUG [adfnn2:16020.archivedHFileCleaner] cleaner.CleanerChore: Removing: hdfs://qhcm/hbase/archive/data/default/THB_USER_FLOW_201610/06cc7d526ab24268202c6cf3bfd1a820/F/9a12d8109b8a44a3bebd743eacb9c071 from archive
2016-12-12 17:59:55,862 DEBUG [adfnn2:16020.archivedHFileCleaner] cleaner.CleanerChore: Removing: hdfs://qhcm/hbase/archive/data/default/THB_USER_FLOW_201610/06cc7d526ab24268202c6cf3bfd1a820/recovered.edits/8503.seqid from archive
提取region分配日志，cat hbase-ocdc-master-adfnn2.log|grep "deleted, state:"|awk ‘{print $7}‘|awk -F ‘,‘ ‘{print $1}‘|sort|uniq，看看哪些表已经被分配
SYSTEM.SEQUENCE THB_GPRS_CHARGE_201610 THB_GPRS_CHARGE_201611 THB_GPRS_CHARGE_201612 THB_GPRS_FLOW_201610 THB_GPRS_FLOW_201611 THB_GPRS_FLOW_201612 THB_GPRS_WAP_201610 THB_GPRS_WAP_201612 THB_USER_FLOW_201610 THB_USER_FLOW_201611 THB_USER_FLOW_201612 THB_USER_INFO_201609 THB_USER_INFO_201610 THB_USER_INFO_201611 THB_USER_INFO_201612 THB_USER_INFO_DAY aidata:user_phone_info_201508 aidata:user_phone_info_201511 aidata:user_phone_info_201512 hbase:meta
hbase:namespace表没有被分配？为什么没有被分配？难道是namespace表有问题导致不能分配？于是让同事把生产环境namespace表目录取下来放到自己的开发环境，namespace表目录比较乱，namespace还嵌namespace，我相信肯定不是维护人员干的，即使namespace嵌套，也不应该影响namepace的region加载。
[email protected] $ hadoop fs -lsr /namespace
lsr: DEPRECATED: Please use ‘ls -R‘ instead.
-rw-r--r-- 1 wangkai8 supergroup 6148 2016-12-12 15:33 /namespace/.DS_Store
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/.tabledesc
-rw-r--r-- 1 wangkai8 supergroup 312 2016-12-12 15:33 /namespace/.tabledesc/.tableinfo.0000000001
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/.tmp
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8
-rw-r--r-- 1 wangkai8 supergroup 6148 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/.DS_Store
-rw-r--r-- 1 wangkai8 supergroup 42 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/.regioninfo
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/info
-rw-r--r-- 1 wangkai8 supergroup 4989 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/info/5b15bf56f4ea443ba6b7e212760f8644
-rw-r--r-- 1 wangkai8 supergroup 4971 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/info/f1c4c097645344269e475ad32cf79913
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/recovered.edits
-rw-r--r-- 1 wangkai8 supergroup 341 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/recovered.edits/0000000000000000480
-rw-r--r-- 1 wangkai8 supergroup 0 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/recovered.edits/11.seqid
-rw-r--r-- 1 wangkai8 supergroup 0 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/recovered.edits/2.seqid
-rw-r--r-- 1 wangkai8 supergroup 0 2016-12-12 15:33 /namespace/83739a75edfb427d8501a43c553caad8/recovered.edits/479.seqid
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/namespace
-rw-r--r-- 1 wangkai8 supergroup 6148 2016-12-12 15:33 /namespace/namespace/.DS_Store
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/namespace/.tabledesc
-rw-r--r-- 1 wangkai8 supergroup 312 2016-12-12 15:33 /namespace/namespace/.tabledesc/.tableinfo.0000000001
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/namespace/.tmp
drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 15:33 /namespace/namespace/51c319c701fe6fdf6b77da884541a4dd
-rw-r--r-- 1 wangkai8 supergroup 42 2016-12-12 15:33 /namespace/namespace/51c319c701fe6fdf6b77da884541a4dd/.regioninfo
把生产环境/hbase1.0.0/data/hbase/namespace/namespace删掉之后再启动集群，结果还是报一样的异常错误，好吧，那就把/hbase1.0.0/data/hbase/namespace/83739a75edfb427d8501a43c553caad8/recovered*删掉再启动集群，结果还是一样。
为了看namespace表到底有哪些记录，把/hbase1.0.0/data/hbase/namespace/83739a75edfb427d8501a43c553caad8/info下两个HFile考到自己开发环境namespace目录下，然后重启hbase集群，可以看到生产环境namespace有哪些记录。
[email protected] ~$ hadoop fs -lsr /hbase1.0.0/data/hbase/namespace lsr: DEPRECATED: Please use ‘ls -R‘ instead. drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 19:16 /hbase1.0.0/data/hbase/namespace/.tabledesc -rw-r--r-- 1 wangkai8 supergroup 312 2016-12-12 19:16 /hbase1.0.0/data/hbase/namespace/.tabledesc/.tableinfo.0000000001 drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 19:16 /hbase1.0.0/data/hbase/namespace/.tmp drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 20:30 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79 -rw-r--r-- 1 wangkai8 supergroup 42 2016-12-12 19:16 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/.regioninfo drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 20:30 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/info -rw-r--r-- 3 wangkai8 supergroup 5041 2016-12-12 20:30 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/info/89830776b101405e9cb2e13d8a770ca6 drwxr-xr-x - wangkai8 supergroup 0 2016-12-15 15:58 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/recovered.edits -rw-r--r-- 3 wangkai8 supergroup 0 2016-12-15 15:58 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/recovered.edits/22.seqid [email protected] ~$ cd Downloads/ [email protected] Downloads$ cd namespace [email protected] namespace$ cd 83739a75edfb427d8501a43c553caad8/ [email protected] 83739a75edfb427d8501a43c553caad8$ ls info recovered.edits [email protected] 83739a75edfb427d8501a43c553caad8$ hadoop fs -put info/* /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/info/ [email protected] 83739a75edfb427d8501a43c553caad8$ hadoop fs -lsr /hbase1.0.0/data/hbase/namespace lsr: DEPRECATED: Please use ‘ls -R‘ instead. drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 19:16 /hbase1.0.0/data/hbase/namespace/.tabledesc -rw-r--r-- 1 wangkai8 supergroup 312 2016-12-12 19:16 /hbase1.0.0/data/hbase/namespace/.tabledesc/.tableinfo.0000000001 drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 19:16 /hbase1.0.0/data/hbase/namespace/.tmp drwxr-xr-x - wangkai8 supergroup 0 2016-12-12 20:30 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79 -rw-r--r-- 1 wangkai8 supergroup 42 2016-12-12 19:16 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/.regioninfo drwxr-xr-x - wangkai8 supergroup 0 2016-12-15 16:01 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/info -rw-r--r-- 1 wangkai8 supergroup 4989 2016-12-15 16:01 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/info/5b15bf56f4ea443ba6b7e212760f8644 -rw-r--r-- 3 wangkai8 supergroup 5041 2016-12-12 20:30 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/info/89830776b101405e9cb2e13d8a770ca6 -rw-r--r-- 1 wangkai8 supergroup 4971 2016-12-15 16:01 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/info/f1c4c097645344269e475ad32cf79913 drwxr-xr-x - wangkai8 supergroup 0 2016-12-15 15:58 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/recovered.edits -rw-r--r-- 3 wangkai8 supergroup 0 2016-12-15 15:58 /hbase1.0.0/data/hbase/namespace/be6712b3ac638d312c7a4544514a6f79/recovered.edits/22.seqid
hbase(main):002:0> scan ‘hbase:namespace‘ ROW COLUMN+CELL default column=info:d, timestamp=1481541361405, value=\x0A\x07default hbase column=info:d, timestamp=1481541361412, value=\x0A\x05hbase ocnosql column=info:d, timestamp=1481541506852, value=\x0A\x07ocnosql 3 row(s) in 0.0980 seconds hbase(main):003:0> scan ‘hbase:namespace‘ ROW COLUMN+CELL aidata column=info:d, timestamp=1441764317452, value=\x0A\x06aidata default column=info:d, timestamp=1481541361405, value=\x0A\x07default hbase column=info:d, timestamp=1481541361412, value=\x0A\x05hbase ocnosql column=info:d, timestamp=1481541506852, value=\x0A\x07ocnosql 4 row(s) in 0.0180 seconds
可以看到namespace多了一条记录，说明namespace hfile也有没问题，那么问题到底在哪？难道hbase:meta表有问题，又让维护同事把meta目录取下来，meta表的HFile就不能直接放到hbase meta目录下了，否则生产环境的region在开发环境肯定找不到导致启动失败。可以通过HFile工具查看HFile里面的数据：
[email protected] info$ hbase org.apache.hadoop.hbase.io.hfile.HFile -e -p -f /meta/1588230740/info/8e498a36f195450d91e07eb8ad4208c1|grep ‘hbase:namespace‘K: hbase:namespace,,1481192140855.83739a75edfb427d8501a43c553caad8./info:regioninfo/1481247939963/Put/vlen=41/seqid=10742 V: PBUF\x08\xB7\xE0\xB9\xEF\x8D+\x12\x12\x0A\x05hbase\x12\x09namespace\x1A\x00"\x00(\x000\x008\x00 [email protected] info$ hbase org.apache.hadoop.hbase.io.hfile.HFile -e -p -f /meta/1588230740/info/bc669ae58e5142d69b6fb38979fcd20c|grep ‘hbase:namespace‘ [email protected] info$
可以看到只有一条记录，且只有一个列，正常namespace表如下
[email protected] ~$ echo ‘scan "hbase:meta"‘|hbase shell|grep "hbase:namespace"
hbase:namespace,,1481791022097.bd5c5e4af06be7540ce00e24c8949399. column=info:regioninfo, timestamp=1481791022263, value={ENCODED => bd5c5e4af06be7540ce00e24c8949399, NAME => ‘hbase:namespace,,1481791022097.bd5c5e4af06be7540ce00e24c8949399.‘, STARTKEY => ‘‘, ENDKEY => ‘‘}
hbase:namespace,,1481791022097.bd5c5e4af06be7540ce00e24c8949399. column=info:seqnumDuringOpen, timestamp=1481791022325, value=\x00\x00\x00\x00\x00\x00\x00\x02
hbase:namespace,,1481791022097.bd5c5e4af06be7540ce00e24c8949399. column=info:server, timestamp=1481791022325, value=wangkai8dembp:61020
hbase:namespace,,1481791022097.bd5c5e4af06be7540ce00e24c8949399. column=info:serverstartcode, timestamp=1481791022325, value=1481791009329
也就是说生产环境namespace表缺少重要的info:server信息，这将导致namespace region在被AssignmentManager分配时跳过。再次查看hbase源码，region分配过程大致如下：
org.apache.hadoop.hbase.master.HMaster#finishActiveMasterInitialization->
org.apache.hadoop.hbase.master.AssignmentManager#joinCluster->
org.apache.hadoop.hbase.master.AssignmentManager#rebuildUserRegions->
org.apache.hadoop.hbase.master.AssignmentManager#processDeadServersAndRegionsInTransition->
org.apache.hadoop.hbase.master.AssignmentManager#assignAllUserRegions->
org.apache.hadoop.hbase.master.AssignmentManager#assign(java.util.Map<org.apache.hadoop.hbase.HRegionInfo,org.apache.hadoop.hbase.ServerName>)->
#创建region bulk plan分配计划
org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer#retainAssignment->
#根据region plan开始真正执行region assign
org.apache.hadoop.hbase.master.AssignmentManager#assign(int, int, String, Map<ServerName,List<HRegionInfo>>)->
org.apache.hadoop.hbase.master.AssignmentManager#assign(ServerName, List<HRegionInfo>)->
//在zookeeper /hbase1.0.0/region-in-transition下创建待分配region信息
org.apache.hadoop.hbase.master.AssignmentManager#asyncSetOfflineInZooKeeper->
org.apache.hadoop.hbase.zookeeper.ZKAssign#asyncCreateNodeOffline->
org.apache.hadoop.hbase.zookeeper.ZKUtil#asyncCreate
生产环境这个异常问题在org.apache.hadoop.hbase.master.AssignmentManager#rebuildUserRegions这个方法，先来看看这个方法里面有什么内容
/**
* Rebuild the list of user regions and assignment information.
* <p>
* Returns a set of servers that are not found to be online that hosted
* some regions.
* @return set of servers not online that hosted some regions per meta
* @throws IOException
*/
Set<ServerName> rebuildUserRegions() throws
IOException, KeeperException, CoordinatedStateException {
Set<TableName> disabledOrEnablingTables = tableStateManager.getTablesInStates(
ZooKeeperProtos.Table.State.DISABLED, ZooKeeperProtos.Table.State.ENABLING);
Set<TableName> disabledOrDisablingOrEnabling = tableStateManager.getTablesInStates(
ZooKeeperProtos.Table.State.DISABLED,
ZooKeeperProtos.Table.State.DISABLING,
ZooKeeperProtos.Table.State.ENABLING);
// Region assignment from META
List<Result> results = MetaTableAccessor.fullScanOfMeta(server.getConnection());
// Get any new but slow to checkin region server that joined the cluster
Set<ServerName> onlineServers = serverManager.getOnlineServers().keySet();
// Set of offline servers to be returned
Set<ServerName> offlineServers = new HashSet<ServerName>();
// Iterate regions in META
for (Result result : results) {
if (result == null && LOG.isDebugEnabled()){
LOG.debug("null result from meta - ignoring but this is strange.");
continue;
}
RegionLocations rl = MetaTableAccessor.getRegionLocations(result);
if (rl == null) continue;
HRegionLocation[] locations = rl.getRegionLocations();
if (locations == null) continue;
for (HRegionLocation hrl : locations) {
HRegionInfo regionInfo = hrl.getRegionInfo();
if (regionInfo == null) continue;
int replicaId = regionInfo.getReplicaId();
State state = RegionStateStore.getRegionState(result, replicaId);
ServerName lastHost = hrl.getServerName(); //由于namespace表info:server为null，导致lastHost也为null
ServerName regionLocation = RegionStateStore.getRegionServer(result, replicaId);
regionStates.createRegionState(regionInfo, state, regionLocation, lastHost); //进而导致namespace region的状态为State.OFFLINE，master不分配此region
if (!regionStates.isRegionInState(regionInfo, State.OPEN)) {
// Region is not open (either offline or in transition), skip
continue;
}
TableName tableName = regionInfo.getTable();
if (!onlineServers.contains(regionLocation)) {
// Region is located on a server that isn‘t online
offlineServers.add(regionLocation);
if (useZKForAssignment) {
regionStates.regionOffline(regionInfo);
}
} else if (!disabledOrEnablingTables.contains(tableName)) {
// Region is being served and on an active server
// add only if region not in disabled or enabling table
regionStates.regionOnline(regionInfo, regionLocation);
balancer.regionOnline(regionInfo, regionLocation);
} else if (useZKForAssignment) {
regionStates.regionOffline(regionInfo);
}
// need to enable the table if not disabled or disabling or enabling
// this will be used in rolling restarts
if (!disabledOrDisablingOrEnabling.contains(tableName)
&& !getTableStateManager().isTableState(tableName,
ZooKeeperProtos.Table.State.ENABLED)) {
setEnabledTable(tableName);
}
}
}
return offlineServers;
}
/**
* Add a region to RegionStates with the specified state.
* If the region is already in RegionStates, this call has
* no effect, and the original state is returned.
*
* @param hri the region info to create a state for
* @param newState the state to the region in set to
* @param serverName the server the region is transitioning on
* @param lastHost the last server that hosts the region
* @return the current state
*/
public synchronized RegionState createRegionState(final HRegionInfo hri,
State newState, ServerName serverName, ServerName lastHost) {
if (newState == null || (newState == State.OPEN && serverName == null)) { //如果region lastHost为null，这个region直接被指定为State.OFFLINE
newState = State.OFFLINE;
}
if (hri.isOffline() && hri.isSplit()) {
newState = State.SPLIT;
serverName = null;
}
String encodedName = hri.getEncodedName();
RegionState regionState = regionStates.get(encodedName);
if (regionState != null) {
LOG.warn("Tried to create a state for a region already in RegionStates, "
+ "used existing: " + regionState + ", ignored new: " + newState);
} else {
regionState = new RegionState(hri, newState, serverName);
regionStates.put(encodedName, regionState);
if (newState == State.OPEN) {
if (!serverName.equals(lastHost)) {
LOG.warn("Open region‘s last host " + lastHost
+ " should be the same as the current one " + serverName
+ ", ignored the last and used the current one");
lastHost = serverName;
}
lastAssignments.put(encodedName, lastHost);
regionAssignments.put(hri, lastHost);
} else if (!regionState.isUnassignable()) {
regionsInTransition.put(encodedName, regionState);
}
if (lastHost != null && newState != State.SPLIT) {
addToServerHoldings(lastHost, hri);
if (newState != State.OPEN) {
oldAssignments.put(encodedName, lastHost);
}
}
}
return regionState;
}
到此根本问题已经定位，meta表数据丢失，原因可能是hbase集群在split操作时维护人员强行kill hbase造成，不管是什么原因导致这个问题，肯定跟hbase自身健壮性有关，不管维护人员在何种状态下stop或kill hbase，也不应该出现meta有问题。meta表本身可以通过hbase hbck -repair来修复，很尴尬的是在集群没启动的情况下hbase hbck用不了。
既然找到了问题，那就想办法解决。麻烦的是集群起不来，meta表没法修复，解决思想有两种：
方案1）修改hbase源码，如果region所属namespace，且server信息为空，人为指定一台regionserver给这个region，使其能被master分配出去，集群能起来，集群起来之后就好办，可以hbck repair meta，也可以进到hbase shell操作meta表。meta表修复之后stop集群，把hbase原来的jar包换回来，启动集群就ok了。
方案2）在开发环境meta表中put一条namespace info:server记录，指定一个regionserver地址，强制执行flush ‘hbase:meta‘，生成包含namespace server信息的HFile，然后把HFile放到生产环境meta目录下，重启之后就可以恢复namespace server信息。
这次采用的解决方案是修改hbase源码，方案二没去验证，根据理论，应该是没问题。
/** * org.apache.hadoop.hbase.MetaTableAccessor#getServerName * 修改此方法，给namespace region指定一个regionserver地址
* Returns a {@link ServerName} from catalog table {@link Result}.
* @param r Result to pull from
* @return A ServerName instance or null if necessary fields not found or empty.
*/
private static ServerName getServerName(final Result r, final int replicaId) {
byte[] serverColumn = getServerColumn(replicaId);
Cell cell = r.getColumnLatestCell(getFamily(), serverColumn);
//---------------------------------------------------------------------------
HRegionInfo regionInfo = getHRegionInfo(r, getRegionInfoColumn());
String tableName = regionInfo.getTable().getNameAsString();
if((cell == null || cell.getValueLength() == 0) && tableName.equals("hbase:namespace")) {
return ServerName.valueOf("adfdn14:16020", 1481534251178L);
}
//---------------------------------------------------------------------------
if (cell == null || cell.getValueLength() == 0) return null;
String hostAndPort = Bytes.toString(
cell.getValueArray(), cell.getValueOffset(), cell.getValueLength());
byte[] startcodeColumn = getStartCodeColumn(replicaId);
cell = r.getColumnLatestCell(getFamily(), startcodeColumn);
if (cell == null || cell.getValueLength() == 0) return null;
return ServerName.valueOf(hostAndPort,
Bytes.toLong(cell.getValueArray(), cell.getValueOffset(), cell.getValueLength()));
}
至此集群已经能正常启动，花了一天时间解决故障。
再来谈谈hbase的设计，master启动时首先分配meta表，然后再分配其它表，但是hbase:namespace系统表和其它用户表分配时同等对待，并没有先分配系统表再分配用户表，如果一个集群region非常多，默认5分钟可能还分配不到namespace表，还得修改hbase.master.namespace.init.timeout超时时间，总感觉有点不合理。
hbase hbck工具是很好用，但是在集群启动不了的情况下，meta表数据没法通过工具来修改，是否可以提供一个离线工具来方便生成HFile，或者提供一个miniCluster在集群瘫痪下能启动起来管理meta、namespace表。
最后想说的是，在生产环境最好不要直接kill掉master和regionserver，否则可能出现意想不到的问题，够你头疼一整子，哈哈