Hbase获取前几条记录

Hbase中hbse shell操作如下：

scan 'Test',{LIMIT=>10}

在java的api中可以通过过滤器来实现操，作如下：

Configuration HBASE_CONFIG = new Configuration();
HBASE_CONFIG.set("hbase.zookeeper.quorum", "XX.XX.XX.XX");
HBASE_CONFIG.set("hbase.zookeeper.property.clientPort", "2181");
hbaseConfig = new HBaseConfiguration(HBASE_CONFIG);
HBaseAdmin hAdmin = new HBaseAdmin(hbaseConfig);
System.out.println(hAdmin.tableExists(TABLE));
HTable table = new HTable(hbaseConfig, TABLE);
Scan scan = new Scan();
scan.setCaching(1);
Filter filter = new PageFilter(20); // 
scan.setFilter(filter);
ResultScanner scanner = table.getScanner(scan);// 执行扫描查找 
int num = 0;
Iterator<Result> res = scanner.iterator();// 返回查询遍历器
	while (res.hasNext()) {
		Result result = res.next();
		num++;
		System.out.println("key:" + new String(result.getRow()));
	}
}

 获取了前20条记录

评论

3 楼 xchd 2013-07-19  

scan.setCaching(20);    
Filter filter = new PageFilter(20); 

和

Filter filter = new PageFilter(20); 
scan.setCaching(20);    

结果是一样的吗？
如果我把scan.setCaching(20); 设置为2000会不会造成影响
谢谢

2 楼 小网客 2013-04-01  

greatwqs 写道

scan.setCaching(20);  
Filter filter = new PageFilter(20);

既然是获取20条数据, 那么就一次从HBase服务器取20条回来; 不20次去取, 每次取一条;

  /**
   * Set the number of rows for caching that will be passed to scanners.
   * If not set, the default setting from {@link HTable#getScannerCaching()} will apply.
   * Higher caching values will enable faster scanners but will use more memory.
   * @param caching the number of rows for caching
   */
  public void setCaching(int caching) {
    this.caching = caching;
  }

嗯 是的 这个code只是个demo

1 楼 greatwqs 2013-03-31  

scan.setCaching(20);  
Filter filter = new PageFilter(20);

既然是获取20条数据, 那么就一次从HBase服务器取20条回来; 不20次去取, 每次取一条;

  /**
   * Set the number of rows for caching that will be passed to scanners.
   * If not set, the default setting from {@link HTable#getScannerCaching()} will apply.
   * Higher caching values will enable faster scanners but will use more memory.
   * @param caching the number of rows for caching
   */
  public void setCaching(int caching) {
    this.caching = caching;
  }