HBase如何在内部分析＆＃34; hbase shell命令＆＃34;？

Question

假设我在hbase shell中运行get 't1','r1'命令， HBase内部如何分析并执行此命令？

Answer 1

这是一个犹豫不决的剧本。这是在shell命令集下定义的。

  

我在这里引用java HashMap作为更好的例子   理解..

• 插入时，你的rowkey就像java HashMap中的键一样，它将存储在一个区域服务器中（在哈希映射的情况下，这些是均匀分布的桶..）
• 在返回行时，它使用rowkey，它将找到特定的区域服务器，并从您提到的表中为其带来值。

  

这就是为什么处理hbase rowkey设计应该是完美的（使用salting技术，使用散列算法，例如mumur hash），它应该均匀分布在区域服务器上以防止热点...   

有关详细信息，请查看get.rb

module Shell
  module Commands
    class Get < Command
      def help
        return <<-EOF
Get row or cell contents; pass table name, row, and optionally
a dictionary of column(s), timestamp, timerange and versions. Examples:
  hbase> get 'ns1:t1', 'r1'
  hbase> get 't1', 'r1'
  hbase> get 't1', 'r1', {TIMERANGE => [ts1, ts2]}
  hbase> get 't1', 'r1', {COLUMN => 'c1'}
  hbase> get 't1', 'r1', {COLUMN => ['c1', 'c2', 'c3']}
  hbase> get 't1', 'r1', {COLUMN => 'c1', TIMESTAMP => ts1}
  hbase> get 't1', 'r1', {COLUMN => 'c1', TIMERANGE => [ts1, ts2], VERSIONS => 4}
  hbase> get 't1', 'r1', {COLUMN => 'c1', TIMESTAMP => ts1, VERSIONS => 4}
  hbase> get 't1', 'r1', {FILTER => "ValueFilter(=, 'binary:abc')"}
  hbase> get 't1', 'r1', 'c1'
  hbase> get 't1', 'r1', 'c1', 'c2'
  hbase> get 't1', 'r1', ['c1', 'c2']
  hbase> get 't1', 'r1', {COLUMN => 'c1', ATTRIBUTES => {'mykey'=>'myvalue'}}
  hbase> get 't1', 'r1', {COLUMN => 'c1', AUTHORIZATIONS => ['PRIVATE','SECRET']}
  hbase> get 't1', 'r1', {CONSISTENCY => 'TIMELINE'}
  hbase> get 't1', 'r1', {CONSISTENCY => 'TIMELINE', REGION_REPLICA_ID => 1}
Besides the default 'toStringBinary' format, 'get' also supports custom formatting by
column.  A user can define a FORMATTER by adding it to the column name in the get
specification.  The FORMATTER can be stipulated: 
 1. either as a org.apache.hadoop.hbase.util.Bytes method name (e.g, toInt, toString)
 2. or as a custom class followed by method name: e.g. 'c(MyFormatterClass).format'.
Example formatting cf:qualifier1 and cf:qualifier2 both as Integers: 
  hbase> get 't1', 'r1' {COLUMN => ['cf:qualifier1:toInt',
    'cf:qualifier2:c(org.apache.hadoop.hbase.util.Bytes).toInt'] } 
Note that you can specify a FORMATTER by column only (cf:qualifier).  You cannot specify
a FORMATTER for all columns of a column family.

The same commands also can be run on a reference to a table (obtained via get_table or
create_table). Suppose you had a reference t to table 't1', the corresponding commands
would be:
  hbase> t.get 'r1'
  hbase> t.get 'r1', {TIMERANGE => [ts1, ts2]}
  hbase> t.get 'r1', {COLUMN => 'c1'}
  hbase> t.get 'r1', {COLUMN => ['c1', 'c2', 'c3']}
  hbase> t.get 'r1', {COLUMN => 'c1', TIMESTAMP => ts1}
  hbase> t.get 'r1', {COLUMN => 'c1', TIMERANGE => [ts1, ts2], VERSIONS => 4}
  hbase> t.get 'r1', {COLUMN => 'c1', TIMESTAMP => ts1, VERSIONS => 4}
  hbase> t.get 'r1', {FILTER => "ValueFilter(=, 'binary:abc')"}
  hbase> t.get 'r1', 'c1'
  hbase> t.get 'r1', 'c1', 'c2'
  hbase> t.get 'r1', ['c1', 'c2']
  hbase> t.get 'r1', {CONSISTENCY => 'TIMELINE'}
  hbase> t.get 'r1', {CONSISTENCY => 'TIMELINE', REGION_REPLICA_ID => 1}
EOF
      end

      def command(table, row, *args)
        get(table(table), row, *args)
      end

      def get(table, row, *args)
        @start_time = Time.now
        formatter.header(["COLUMN", "CELL"])

        count, is_stale = table._get_internal(row, *args) do |column, value|
          formatter.row([ column, value ])
        end

        formatter.footer(count, is_stale)
      end
    end
  end
end

#add get command to table
::Hbase::Table.add_shell_command('get')

如果您想要像hbase shell命令一样获得一条记录，可以按照以下代码段进行操作。

根据您的评论进行更新：如果您想在java中使用相同的功能

 /**
     * Get a row
     */
    @Override
    public void getOneRecord(final String tableName, final String rowKey) throws IOException {
        final HTable table = new HTable(HBaseConn.getHBaseConfig(), getTable(tableName));
        final Get get = new Get(rowKey.getBytes());
        final Result rs = table.get(get);
        for (final KeyValue kv : rs.raw()) {
            LOG.info(kv.getRow() + " " + kv.getFamily() + ":" + kv.getQualifier() + " " + +kv.getTimestamp());
            LOG.info(new String(kv.getValue()));
        }
    }

注意：有java方法和shell方法是2个不同的东西。请。不要混合两者，为I have seen your other questions as well，我觉得你对它们有点困惑。如果你想像我解释的那样写jruby，你也可以这样做。但那不是常用的做法。

希望有所帮助。