漫談Cassandra客戶端的使用
作者：逖靖寒
本文將介紹的是關于NoSQL數(shù)據(jù)庫Cassandra客戶端的使用，希望本文能對大家有所幫助。
51CTO數(shù)據(jù)庫頻道之前也曾有過《NoSOL:關系型數(shù)據(jù)庫終結(jié)者？》專題，希望大家能更深入的了解NoSQL。
最近試用了一段時間Cassandra，將Oracle中的數(shù)據(jù)導入進來，遇到了問題然后解決問題，收獲挺大。在這個過程中，除了設計一個合理的數(shù)據(jù)模型，再就是使用Cassandra API進行交互了。
Cassandra在設計的時候，就是支持Thrift的，這意味著我們可以使用多種語言開發(fā)。
對于Cassandra的開發(fā)本身而言，這是使用Thrift的好處：支持多語言。壞處也是顯而易見的：Thrift API功能過于簡單，不具備在生產(chǎn)環(huán)境使用的條件。
在Cassandra Wiki頁面上，也有基于Thrift API開發(fā)的更加高級的API，各個語言都有，具體信息可以參考：http://wiki.apache.org/cassandra/ClientExamples。
這次只談談下面兩類Java的客戶端：
1 Thrift Java API
2 hector
Thrift Java API
這個是Cassandra自帶的最簡單的一類API，這個文件在apache-cassandra-0.5.1.jar中包含了?？梢灾苯邮褂?。我們也可以自己安裝一個Thrift，然后通過cassandra.thrift文件自動生成。
如果你要使用Cassandra，那么我們必須要了解Thrift API，畢竟所有的其他更加高級的API都是基于這個來包裝的。
提供的功能
插入數(shù)據(jù)
插入數(shù)據(jù)需要指定keyspace，ColumnFamily， Column，Key，Value，timestamp和數(shù)據(jù)同步級別。（如何需要了Cassandra的解數(shù)據(jù)模型，可以參考《大話Cassandra數(shù)據(jù)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
讀取數(shù)據(jù)
獲取一個查詢條件精確的值。
- /** * 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
獲取某一個keyspace，Key，ColumnFamily，SuperColumn（如果有的話需要指定）下面的相關數(shù)據(jù)：只查詢Column的name符合條件的相關數(shù)據(jù)（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;
查詢Key的取值范圍（使用這個功能需要使用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
查詢系統(tǒng)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;
通過這些操作，我們可以了解到系統(tǒng)的信息。
其中一個比較有意思的查詢信息是：token map，通過這個我們可以知道哪些Cassandra Service是可以提供服務的。
刪除數(shù)據(jù)
- /**
- * 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
這里需要注意的是，由于一致性的問題。這里的刪除操作不會立即刪除所有機器上的該數(shù)據(jù)，但是最終會一致。
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, "網(wǎng)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();
- }}
優(yōu)點與缺點
優(yōu)點：簡單高效
缺點：功能簡單，無法提供連接池，錯誤處理等功能，不適合直接在生產(chǎn)環(huán)境使用。
Hector
Hector是基于Thrift Java API包裝的一個Java客戶端，提供一個更加高級的一個抽象。
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("網(wǎng)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);
- } }}
優(yōu)點
1 提供連接池。
2 提供錯誤處理：當操作失敗的時候，Hector會根據(jù)系統(tǒng)信息（token map）自動連接另一個Cassandra Service。
3 編程接口容易使用。
4 支持JMX。
缺點
1 不支持多線程的環(huán)境。
2 keyspace封裝過多（數(shù)據(jù)校驗和數(shù)據(jù)重新封裝），如果進行大量的數(shù)據(jù)操作，這里的消耗需要考慮。
3 錯誤處理不夠人性化：如果所有的Cassandra Service都非常繁忙，那么經(jīng)過多次操作失敗后，最終的結(jié)果失敗。
總結(jié)
Hector已經(jīng)是一個基本足夠使用的Java客戶端了，但是還是缺乏一些相關的功能，比如：
1 線程安全。
2 支持自動的多線程查詢和插入，提高操作效率。
3 人性化的錯誤處理機制。
4 避免過多的封裝。
原文標題：談談Cassandra的客戶端
鏈接： http://www.cnblogs.com/gpcuster/archive/2010/03/23/1692794.html
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責任編輯：彭凡
來源：
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