假设一个具有20行的Cassandra数据存储,行键名为"r1"
.. "r20"
。获取Cassandra行键
问题:
如何取前十行的行键(
r1
到r10
)?如何获取下10行的行密钥(
r11
至r20
)?
我在寻找卡桑德拉比喻:
SELECT row_key FROM table LIMIT 0, 10;
SELECT row_key FROM table LIMIT 10, 10;
假设一个具有20行的Cassandra数据存储,行键名为"r1"
.. "r20"
。获取Cassandra行键
问题:
如何取前十行的行键(r1
到r10
)?
如何获取下10行的行密钥(r11
至r20
)?
我在寻找卡桑德拉比喻:
SELECT row_key FROM table LIMIT 0, 10;
SELECT row_key FROM table LIMIT 10, 10;
看看:
list<KeySlice> get_range_slices(keyspace, column_parent, predicate, range, consistency_level)
如果您KeyRange的元组是(start_key,end_key)==(R1 ,r10)
您应该首先在cassandra1.1.o版本中修改cassandra.yaml
,您应该在其中设置如下:
partitioner: org.apache.cassandra.dht.ByteOrderedPartitioner
其次,你应该定义如下:
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,您可以将数据插入到卡桑德拉和可实现范围查询。
根据我的测试,行没有顺序(与列不同)。 CQL 3.0.0可以检索行密钥,但不能区分(应该有一种我不知道的方式)。我的情况我不知道我的密钥范围是什么,所以我尝试使用Hector和Thrift检索所有密钥并在稍后对键进行排序。使用CQL 3.0.0进行的100000列200行性能测试大约为500毫秒,Hector大约为100,节约大约50毫秒。我的行键在这里是整数。赫克托代码如下:
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);
}
}
这是节俭代码:
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();
}
}