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module Shell
  module Commands
    class Alter < Command
      def help
        <<-EOF
Alter a table. Tables can be altered without disabling them first.
Altering enabled tables has caused problems
in the past, so use caution and test it before using in production.

You can use the alter command to add,
modify or delete column families or change table configuration options.
Column families work in a similar way as the 'create' command. The column family
specification can either be a name string, or a dictionary with the NAME attribute.
Dictionaries are described in the output of the 'help' command, with no arguments.

For example, to change or add the 'f1' column family in table 't1' from
current value to keep a maximum of 5 cell VERSIONS, do:

  hbase> alter 't1', NAME => 'f1', VERSIONS => 5

You can operate on several column families:

  hbase> alter 't1', 'f1', {NAME => 'f2', IN_MEMORY => true}, {NAME => 'f3', VERSIONS => 5}

To delete the 'f1' column family in table 'ns1:t1', use one of:

  hbase> alter 'ns1:t1', NAME => 'f1', METHOD => 'delete'
  hbase> alter 'ns1:t1', 'delete' => 'f1'

You can also change table-scope attributes like MAX_FILESIZE, READONLY,
MEMSTORE_FLUSHSIZE, NORMALIZATION_ENABLED, NORMALIZER_TARGET_REGION_COUNT,
NORMALIZER_TARGET_REGION_SIZE_MB, DURABILITY, etc. These can be put at the end;
for example, to change the max size of a region to 128MB, do:

  hbase> alter 't1', MAX_FILESIZE => '134217728'

You can add a table coprocessor by setting a table coprocessor attribute. Only the CLASSNAME is
required in the coprocessor specification.

  hbase> alter 't1', COPROCESSOR => {
           CLASSNAME => 'org.apache.hadoop.hbase.coprocessor.SimpleRegionObserver',
           JAR_PATH => 'hdfs:///foo.jar',
           PRIORITY => 12,
           PROPERTIES => {'a' => '17' }
         }

Since you can have multiple coprocessors configured for a table, a
sequence number will be automatically appended to the attribute name
to uniquely identify it. For example, the attribute name might be "coprocessor$1".

You can also set configuration settings specific to this table or column family:

  hbase> alter 't1', CONFIGURATION => {'hbase.hregion.scan.loadColumnFamiliesOnDemand' => 'true'}
  hbase> alter 't1', {NAME => 'f2', CONFIGURATION => {'hbase.hstore.blockingStoreFiles' => '10'}}

You can also set configuration setting with REOPEN_REGIONS=>'false' to avoid regions RIT, which
let the modification take effect after regions was reopened (Be careful, the regions of the table
may be configured inconsistently If regions are not reopened after the modification)

  hbase> alter 't1', REOPEN_REGIONS => 'false', MAX_FILESIZE => '134217728'
  hbase> alter 't1', REOPEN_REGIONS => 'false', CONFIGURATION => {'hbase.hregion.scan
    .loadColumnFamiliesOnDemand' => 'true'}

However, be aware that:
1. Inconsistency Risks: If the regions are not reopened after the modification, the table's regions
may become inconsistently configured. Ensure that you manually reopen the regions as soon as
possible to apply the changes consistently across the entire table.
2. If changes are made to the table without reopening the regions, we currently only allow
lightweight operations. The following types of changes, which may lead to unknown situations,
will throw an exception:
    a. Adding or removing CFs, coprocessors.
    b. Modifying the table name.
    c. Changing region replica related configurations such as 'REGION_REPLICATION'
       and 'REGION_MEMSTORE_REPLICATION'.
    d. Changing the rsgroup.

You can also unset configuration settings specific to this table:

  hbase> alter 't1', METHOD => 'table_conf_unset', NAME => 'hbase.hregion.majorcompaction'

You can also remove a table-scope attribute:

  hbase> alter 't1', METHOD => 'table_att_unset', NAME => 'MAX_FILESIZE'

  hbase> alter 't1', METHOD => 'table_att_unset', NAME => 'coprocessor$1'

Other than removing coprocessor from the table-scope attribute via 'table_att_unset', you can also
use 'table_remove_coprocessor' by specifying the class name:

  hbase> alter 't1', METHOD => 'table_remove_coprocessor', CLASSNAME =>
           'org.apache.hadoop.hbase.coprocessor.SimpleRegionObserver'

You can also remove multiple coprocessors at once:

  hbase> alter 't1', METHOD => 'table_remove_coprocessor', CLASSNAME =>
           ['org.apache.hadoop.hbase.coprocessor.SimpleRegionObserver',
            'org.apache.hadoop.hbase.coprocessor.Export']

You can also set REGION_REPLICATION:

  hbase> alter 't1', {REGION_REPLICATION => 2}

You can disable/enable table split and/or merge:

  hbase> alter 't1', {SPLIT_ENABLED => false}
  hbase> alter 't1', {MERGE_ENABLED => false}

There could be more than one alteration in one command:

  hbase> alter 't1', { NAME => 'f1', VERSIONS => 3 },
   { MAX_FILESIZE => '134217728' }, { METHOD => 'delete', NAME => 'f2' },
   METADATA => { 'mykey' => 'myvalue' }
EOF
      end

      def command(table, *args)
        admin.alter(table, true, *args)
      end
    end
  end
end
