取Cassandra行的钥匙

Question

假设一个卡桑德拉的数据存储20排，与行键名 "r1" .. "r20".

问题：

• 我怎么取的行键的第十行(r1 要 r10)?

• 我怎么取的行键的下一个十行(r11 要 r20)?

我在找卡桑德拉比喻：

SELECT row_key FROM table LIMIT 0, 10;
SELECT row_key FROM table LIMIT 10, 10;

Answer 1

看看:

list<KeySlice> get_range_slices(keyspace, column_parent, predicate, range, consistency_level)

你KeyRange元组(start_key,end_key)==(r1,r10)

Answer 2

根据我的测试有没有顺序的行(不同于列)。CQL为3.0.0可以检索的行键，但不是不同的(应该有一种方式，我不知道)。我我我不知道我是什么关键的范围，所以我想来检索所有的钥匙都Hector和节俭，并排序的钥匙后。性能测试与CQL为3.0.0为100000列200行大约是500毫秒，赫克托约100和节俭约50毫秒。我的行关键在这里是整数。赫克托的代码如下：

public void qureyRowkeys(){
    myCluster = HFactory.getOrCreateCluster(CLUSTER_NAME, "127.0.0.1:9160");
    ConfigurableConsistencyLevel ccl = new ConfigurableConsistencyLevel();
    ccl.setDefaultReadConsistencyLevel(HConsistencyLevel.ONE);
    myKeyspace = HFactory.createKeyspace(KEYSPACE_NAME, myCluster, ccl);
    RangeSlicesQuery<Integer, Composite, String> rangeSlicesQuery = HFactory.createRangeSlicesQuery(myKeyspace, IntegerSerializer.get(), 
            CompositeSerializer.get(), StringSerializer.get());
    long start = System.currentTimeMillis();
    QueryResult<OrderedRows<Integer, Composite, String>> result =
      rangeSlicesQuery.setColumnFamily(CF).setKeys(0, -1).setReturnKeysOnly().execute();
    OrderedRows<Integer, Composite, String> orderedRows = result.get();
    ArrayList<Integer> list = new ArrayList<Integer>();
    for(Row<Integer, Composite, String> row: orderedRows){
        list.add(row.getKey());
    }

    System.out.println((System.currentTimeMillis()-start));
    Collections.sort(list);
    for(Integer i: list){
        System.out.println(i);
    }
}

这是节俭码：

public void retreiveRows(){
    try {
        transport = new TFramedTransport(new TSocket("localhost", 9160));
        TProtocol protocol = new TBinaryProtocol(transport);
        client = new Cassandra.Client(protocol);
        transport.open();
        client.set_keyspace("prefdb");
        ColumnParent columnParent = new ColumnParent("events"); 
        SlicePredicate predicate = new SlicePredicate();
        predicate.setSlice_range(new SliceRange(ByteBuffer.wrap(new byte[0]), ByteBuffer.wrap(new byte[0]), false, 1));              
        KeyRange keyRange = new KeyRange();  //Get all keys
        keyRange.setStart_key(new byte[0]);
        keyRange.setEnd_key(new byte[0]);
        long start = System.currentTimeMillis();
        List<KeySlice> keySlices = client.get_range_slices(columnParent, predicate, keyRange, ConsistencyLevel.ONE);
        ArrayList<Integer> list = new ArrayList<Integer>();
        for (KeySlice ks : keySlices) {
                 list.add(ByteBuffer.wrap(ks.getKey()).getInt());
        }    
        Collections.sort(list);
        System.out.println((System.currentTimeMillis()-start));
        for(Integer i: list){
            System.out.println(i);
        }

        transport.close();
    } catch (Exception e) {
        e.printStackTrace();

    }
}

Answer 3

你应该先修改 cassandra.yaml 在该版本的cassandra1.1.噢，你应该设置如下：

partitioner: org.apache.cassandra.dht.ByteOrderedPartitioner

其次，应该定义如下：

create keyspace DEMO with placement_strategy =
  'org.apache.cassandra.locator.SimpleStrategy' and
  strategy_options = [{replication_factor:1}];

use DEMO;

create column family Users with comparator = AsciiType and
  key_validation_class = LongType and
  column_metadata = [
    {
      column_name: aaa,
      validation_class: BytesType
    },{
      column_name: bbb,
      validation_class: BytesType
    },{
      column_name: ccc,
      validation_class: BytesType
    }
  ];

最后，可以插入数据卡桑德拉和可实现的范围内查询。