51CTO数据库频道之前也曾有过《NoSOL:关系型数据库终结者?》专题,希望大家能更深入的了解NoSQL。
最近试用了一段时间Cassandra,将Oracle中的数据导入进来,遇到了问题然后解决问题,收获挺大。在这个过程中,除了设计一个合理的数据模型,再就是使用Cassandra API进行交互了。
Cassandra在设计的时候,就是支持Thrift的,这意味着我们可以使用多种语言开发。
对于Cassandra的开发本身而言,这是使用Thrift的好处:支持多语言。坏处也是显而易见的:Thrift API功能过于简单,不具备在生产环境使用的条件。
在Cassandra Wiki页面上,也有基于Thrift API开发的更加高级的API,各个语言都有,具体信息可以参考:http://wiki.apache.org/cassandra/ClientExamples。
这次只谈谈下面两类Java的客户端:
1 Thrift Java API
2 hector
Thrift Java API
这个是Cassandra自带的最简单的一类API,这个文件在apache-cassandra-0.5.1.jar中包含了。可以直接使用。我们也可以自己安装一个Thrift,然后通过cassandra.thrift文件自动生成。
如果你要使用Cassandra,那么我们必须要了解Thrift API,毕竟所有的其他更加高级的API都是基于这个来包装的。
提供的功能
插入数据
插入数据需要指定keyspace,ColumnFamily, Column,Key,Value,timestamp和数据同步级别。(如何需要了Cassandra的解数据模型,可以参考《大话Cassandra数据模型》)
- /** * Insert a Column consisting of (column_path.column, value, timestamp)
- at the given column_path.column_family and optional
- * column_path.super_column. Note that column_path.column is here required,
- since a SuperColumn cannot directly contain binary
- * values -- it can only contain sub-Columns.
- *
- * @param keyspace
- * @param key
- * @param column_path
- * @param value
- * @param timestamp
- * @param consistency_level
- */public void insert(String keyspace, String key, ColumnPath column_path, byte[] value, long timestamp, int consistency_level) throws InvalidRequestException, UnavailableException, TimedOutException, TException;
- /** * Insert Columns or SuperColumns across different Column Families for the same row key. batch_mutation is a
- * map<string, list<ColumnOrSuperColumn>> -- a map which pairs column family names with the relevant ColumnOrSuperColumn
- * objects to insert.
- *
- * @param keyspace
- * @param key
- * @param cfmap
- * @param consistency_level
- */public void batch_insert(String keyspace, String key, Map<String,List<ColumnOrSuperColumn>> cfmap, int consistency_level) throws InvalidRequestException, UnavailableException
读取数据
获取一个查询条件精确的值。
- /** * Get the Column or SuperColumn at the given column_path. If no value is present, NotFoundException is thrown. (This is
- * the only method that can throw an exception under non-failure conditions.)
- * * @param keyspace
- * @param key
- * @param column_path
- * @param consistency_level
- */public ColumnOrSuperColumn get(String keyspace, String key, ColumnPath column_path,
- int consistency_level) throws InvalidRequestException, NotFoundException, UnavailableException, TimedOutException, TException;
- /** * Perform a get for column_path in parallel on the given list<string> keys. The return value maps keys to the
- * ColumnOrSuperColumn found. If no value corresponding to a key is present, the key will still be in the map, but both
- * the column and super_column references of the ColumnOrSuperColumn object it maps to will be null.
- * * @param keyspace
- * @param keys * @param column_path
- * @param consistency_level
- */public Map<String,ColumnOrSuperColumn> multiget(String keyspace, List<String> keys,
- ColumnPath column_path, int consistency_level) throws InvalidRequestException
获取某一个keyspace,Key,ColumnFamily,SuperColumn(如果有的话需要指定)下面的相关数据:只查询Column的name符合条件的相关数据(SlicePredicate)。
- /** * Get the group of columns contained by column_parent (either a ColumnFamily name or a ColumnFamily/SuperColumn name
- * pair) specified by the given SlicePredicate. If no matching values are found, an empty list is returned.
- * * @param keyspace
- * @param key
- * @param column_parent
- * @param predicate
- * @param consistency_level
- */public List<ColumnOrSuperColumn> get_slice(String keyspace, String key, ColumnParent column_parent, SlicePredicate predicate,
- int consistency_level) throws InvalidRequestException, UnavailableException, TimedOutException, TException; /*
- * * Performs a get_slice for column_parent and predicate for the given keys in parallel.
- *
- * @param keyspace
- * @param keys
- * @param column_parent
- * @param predicate
- * @param consistency_level
- */public Map<String,List<ColumnOrSuperColumn>> multiget_slice(String keyspace, List<String> keys, ColumnParent column_parent,
- SlicePredicate predicate, int consistency_level) throws InvalidRequestException, UnavailableException, TimedOutException, TException;
查询Key的取值范围(使用这个功能需要使用order-preserving partitioner)。
- /** * @deprecated; use get_range_slice instead
- *
- * @param keyspace
- * @param column_family
- * @param start
- * @param finish
- * @param count
- * @param consistency_level
- */public List<String> get_key_range(String keyspace, String column_family,
- String start, String finish, int count, int consistency_level)
- throws InvalidRequestException, UnavailableException, TimedOutException, TException; /*
- *
- * returns a subset of columns for a range of keys.
- *
- * @param keyspace
- * @param column_parent
- * @param predicate
- * @param start_key
- * @param finish_key
- * @param row_count
- * @param consistency_level
- */public List<KeySlice> get_range_slice(String keyspace, ColumnParent column_parent,
- SlicePredicate predicate, String start_key, String finish_key, int row_count
查询系统的信息。
- /**
- * get property whose value is of type string.
- *
- * @param property
- */public String get_string_property(String property) throws TException; /*
- *
- * get property whose value is list of strings.
- *
- * @param property */public List<String> get_string_list_property(String property) throws TException; /*
- *
- * describe specified keyspace
- *
- * @param keyspace
- */public Map<String,Map<String,String>> describe_keyspace(String keyspace)
- throws NotFoundException, TException;
通过这些操作,我们可以了解到系统的信息。
其中一个比较有意思的查询信息是:token map,通过这个我们可以知道哪些Cassandra Service是可以提供服务的。
删除数据
- /**
- * Remove data from the row specified by key at the granularity specified by column_path,
- and the given timestamp. Note
- * that all the values in column_path besides column_path.column_family are truly optional: you can remove the entire
- * row by just specifying the ColumnFamily, or you can remove a SuperColumn
- or a single Column by specifying those levels too.
- *
- * @param keyspace
- * @param key
- * @param column_path
- * @param timestamp
- * @param consistency_level
- */public void remove(String keyspace, String key, ColumnPath column_path,
- long timestamp, int consistency_level) throws InvalidRequestException, UnavailableException
这里需要注意的是,由于一致性的问题。这里的删除操作不会立即删除所有机器上的该数据,但是最终会一致。
程序范例
- import java.util.List;
- import java.io.UnsupportedEncodingException;
- import org.apache.thrift.transport.TTransport;
- import org.apache.thrift.transport.TSocket;
- import org.apache.thrift.protocol.TProtocol;
- import org.apache.thrift.protocol.TBinaryProtocol;
- import org.apache.thrift.TException;
- import org.apache.cassandra.service.*;
- public class CClient{
- public static void main(String[] args)
- throws TException, InvalidRequestException,
- UnavailableException, UnsupportedEncodingException, NotFoundException
- {
- TTransport tr = new TSocket("localhost", 9160);
- TProtocol proto = new TBinaryProtocol(tr);
- Cassandra.Client client = new Cassandra.Client(proto);
- tr.open();
- String key_user_id = "逖靖寒的世界";
- // insert data
- long timestamp = System.currentTimeMillis();
- client.insert("Keyspace1", key_user_id,
- new ColumnPath("Standard1", null, "网址".getBytes("UTF-8")),
- "http://gpcuster.cnblogs.com".getBytes("UTF-8"), timestamp,ConsistencyLevel.ONE);
- client.insert("Keyspace1", key_user_id,
- new ColumnPath("Standard1", null, "作者".getBytes("UTF-8")),
- "逖靖寒".getBytes("UTF-8"), timestamp, ConsistencyLevel.ONE);
- // read single column
- ColumnPath path = new ColumnPath("Standard1", null, "name".getBytes("UTF-8"));
- System.out.println(client.get("Keyspace1", key_user_id, path, ConsistencyLevel.ONE));
- // read entire row
- SlicePredicate predicate = new SlicePredicate(null, new SliceRange(new byte[0], new byte[0], false, 10));
- ColumnParent parent = new ColumnParent("Standard1", null);
- List<ColumnOrSuperColumn> results = client.get_slice("Keyspace1", key_user_id, parent, predicate, ConsistencyLevel.ONE);
- for (ColumnOrSuperColumn result : results) {
- Column column = result.column;
- System.out.println(new String(column.name, "UTF-8") + " -> " + new String(column.value, "UTF-8"));
- }
- tr.close();
- }}
优点与缺点
优点:简单高效
缺点:功能简单,无法提供连接池,错误处理等功能,不适合直接在生产环境使用。
Hector
Hector是基于Thrift Java API包装的一个Java客户端,提供一个更加高级的一个抽象。
程序范例
- package me.prettyprint.cassandra.service;
- import static me.prettyprint.cassandra.utils.StringUtils.bytes;
- import static me.prettyprint.cassandra.utils.StringUtils.string;
- import org.apache.cassandra.service.Column;
- import org.apache.cassandra.service.ColumnPath;
- public class ExampleClient {
- public static void main(String[] args) throws IllegalStateException, PoolExhaustedException,
- Exception {
- CassandraClientPool pool = CassandraClientPoolFactory.INSTANCE.get(); CassandraClient client = pool.borrowClient("localhost", 9160);
- // A load balanced version would look like this:
- // CassandraClient client = pool.borrowClient(new String[] {"cas1:9160", "cas2:9160", "cas3:9160"});
- try {
- Keyspace keyspace = client.getKeyspace("Keyspace1");
- ColumnPath columnPath = new ColumnPath("Standard1", null, bytes("网址"));
- // insert
- keyspace.insert("逖靖寒的世界", columnPath, bytes("http://gpcuster.cnblogs.com"));
- // read
- Column col = keyspace.getColumn("逖靖寒的世界", columnPath); System.out.println("Read from cassandra: " + string(col.getValue()));
- } finally {
- // return client to pool. do it in a finally block to make sure it's executed
- pool.releaseClient(client);
- } }}
优点
1 提供连接池。
2 提供错误处理:当操作失败的时候,Hector会根据系统信息(token map)自动连接另一个Cassandra Service。
3 编程接口容易使用。
4 支持JMX。
缺点
1 不支持多线程的环境。
2 keyspace封装过多(数据校验和数据重新封装),如果进行大量的数据操作,这里的消耗需要考虑。
3 错误处理不够人性化:如果所有的Cassandra Service都非常繁忙,那么经过多次操作失败后,最终的结果失败。
总结
Hector已经是一个基本足够使用的Java客户端了,但是还是缺乏一些相关的功能,比如:
1 线程安全。
2 支持自动的多线程查询和插入,提高操作效率。
3 人性化的错误处理机制。
4 避免过多的封装。
原文标题:谈谈Cassandra的客户端
链接: http://www.cnblogs.com/gpcuster/archive/2010/03/23/1692794.html