一、什么是namespace

在RDBMS中有database的概念，用来对table进行分组，那么在HBase中当表比较多的时候如何对表分组呢，就是namespace，可以简单的把namespace理解为RDBMS中的database。

二、namespace相关操作

内置的namespace

HBase有两个内置的namespace：

hbase(main):009:0> list_namespace

NAMESPACE

default

hbase

2 row(s)

Took 0.0683 seconds

hbase：用来存放系统相关的一些元数据等，相当于mysql中的mysql数据库：

hbase(main):025:0> list_namespace_tables "hbase""

TABLE

meta

namespace

2 row(s)

Took 0.0174 seconds

=> ["meta", "namespace"]

default：创建表时未指定命名空间的话默认挂在default下。

创建namespace

创建namespace：

hbase(main):010:0> create_namespace "test"

Took 0.2781 seconds

在创建namespace的时候还可以添加一些说明信息：

hbase(main):018:0> create_namespace "test002", {"author"=>"CC11001100", "create_time"=>"2018-11-4 17:51:53"}

Took 0.2262 seconds

查看namespace信息

上面创建namespace时添加了一些附加信息，如何查看这些附加信息呢：

hbase(main):019:0> describe_namespace "test002""

DESCRIPTION

{NAME => 'test002', author => 'CC11001100', create_time => '2018-11-4 17:51:53'}

Took 0.0042 seconds

=> 1

修改namespace

查看附加信息发现作者写错了，需要修改：

hbase(main):014:0> alter_namespace "test002", {METHOD=>"set", "author"=>"ChenEr"}

Took 0.2458 seconds

hbase(main):015:0> describe_namespace "test002"

DESCRIPTION

{NAME => 'test002', author => 'ChenEr', create_time => '2018-11-4 17:51:53'}

Took 0.0056 seconds

=> 1

改完发现还漏了一项，需要追加自己的联系方式：

hbase(main):016:0> alter_namespace "test002", {METHOD=>"set", "email"=>"CC11001100@qq.com"}

Took 0.2313 seconds

hbase(main):017:0> describe_namespace "test002"

DESCRIPTION

{NAME => 'test002', author => 'ChenEr', create_time => '2018-11-4 17:51:53', email => 'CC11001100@qq.com'}

Took 0.0038 seconds

=> 1

想了下放上去自己的联系方式搞不好会被不断骚扰，还是去掉此项属性：

hbase(main):010:0> alter_namespace "test002", {METHOD=>"unset", NAME=>"email"}

Took 0.2419 seconds

hbase(main):011:0> describe_namespace "test002"

DESCRIPTION

{NAME => 'test002', author => 'ChenEr', create_time => '2018-11-4 17:51:53'}

Took 0.0056 seconds

=> 1

总结：

添加或修改属性：

alter_namespace 'ns1', {METHOD => 'set', 'PROPERTY_NAME' => 'PROPERTY_VALUE'}

删除属性：

alter_namespace 'ns1', {METHOD => 'unset', NAME=>'PROPERTY_NAME'}

查看已创建的所有namespace

查看当前已经创建的namespace，相当于RDBMS中的show databases：

hbase(main):019:0> list_namespace

NAMESPACE

default

hbase

test

test002

4 row(s)

Took 0.0122 seconds

删除namespace

删除namespace：

hbase(main):019:0> list_namespace

NAMESPACE

default

hbase

test

test002

4 row(s)

Took 0.0122 seconds

hbase(main):020:0> drop_namespace "test002"

Took 0.2321 seconds

hbase(main):021:0> list_namespace

NAMESPACE

default

hbase

test

3 row(s)

Took 0.0111 seconds

注意要删除的namespace必须是空的，其下没有表，否则会删除失败：

hbase(main):051:0> create_namespace "test_drop_namespace"

Took 0.2376 seconds

hbase(main):052:0> create "test_drop_namespace:t1", "cf1"

Created table test_drop_namespace:t1

Took 2.2312 seconds

=> Hbase::Table - test_drop_namespace:t1

hbase(main):053:0> drop_namespace "test_drop_namespace"

ERROR: org.apache.hadoop.hbase.constraint.ConstraintException: Only empty namespaces can be removed. Namespace test_drop_namespace has 1 tables

    at org.apache.hadoop.hbase.master.procedure.DeleteNamespaceProcedure.prepareDelete(DeleteNamespaceProcedure.java:217)

    at org.apache.hadoop.hbase.master.procedure.DeleteNamespaceProcedure.executeFromState(DeleteNamespaceProcedure.java:78)

    at org.apache.hadoop.hbase.master.procedure.DeleteNamespaceProcedure.executeFromState(DeleteNamespaceProcedure.java:45)

    at org.apache.hadoop.hbase.procedure2.StateMachineProcedure.execute(StateMachineProcedure.java:189)

    at org.apache.hadoop.hbase.procedure2.Procedure.doExecute(Procedure.java:850)

    at org.apache.hadoop.hbase.procedure2.ProcedureExecutor.execProcedure(ProcedureExecutor.java:1473)

    at org.apache.hadoop.hbase.procedure2.ProcedureExecutor.executeProcedure(ProcedureExecutor.java:1241)

    at org.apache.hadoop.hbase.procedure2.ProcedureExecutor.access$800(ProcedureExecutor.java:75)

    at org.apache.hadoop.hbase.procedure2.ProcedureExecutor$WorkerThread.run(ProcedureExecutor.java:1761)

For usage try 'help "drop_namespace"'

Took 0.1217 seconds

hbase(main):054:0> disable "test_drop_namespace:t1"

Took 0.4357 seconds

hbase(main):055:0> drop "test_drop_namespace:t1"

Took 0.2351 seconds

hbase(main):056:0> drop_namespace "test_drop_namespace"

Took 0.2172 seconds

创建表时指定namespace

创建表时指定表所在的namespace，使用namespace-name:tale-name的格式指定：

hbase(main):022:0> create "test:user", "userInfo"

Created table test:user

Took 2.3992 seconds

=> Hbase::Table - test:user

查看namespace下的表

查看namespace下都有哪些表：

hbase(main):024:0> list_namespace_tables "test"

TABLE

user

1 row(s)

Took 0.0252 seconds

=> ["user"]

巴特西

Hbase的namespace命令操作