35MyCat - 分片规则（字符串hash解析）

此规则是截取字符串中的int数值hash分片

 
	
		 user_id
		  sharding-by-stringhash 
	   
  
  
  512  
	  2 0:2 
  

配置说明：
上面columns 标识将要分片的表字段，algorithm 分片函数

函数中length代表字符串hash求模基数，count分区数，hashSlice hash预算位，即根据子字符串中int值 hash运算

hashSlice ： 0 means str.length(), -1 means str.length()-1
/**

• “2” -> (0,2)
• “1:2” -> (1,2)
• “1:” -> (1,0)
• “-1:” -> (-1,0)
• “:-1” -> (0,-1)
• “:” -> (0,0)
  */
  例子：

String idVal=null;
 rule.setPartitionLength("512");
 rule.setPartitionCount("2");
 rule.init();
 rule.setHashSlice("0:2");
// idVal = "0";
// Assert.assertEquals(true, 0 == rule.calculate(idVal));
// idVal = "45a";
// Assert.assertEquals(true, 1 == rule.calculate(idVal));
 //last 4
 rule = new PartitionByString();
 rule.setPartitionLength("512");
 rule.setPartitionCount("2");
 rule.init();
 //last 4 characters
 rule.setHashSlice("-4:0");
 idVal = "aaaabbb0000";
 Assert.assertEquals(true, 0 == rule.calculate(idVal));
 idVal = "aaaabbb2359";
 Assert.assertEquals(true, 0 == rule.calculate(idVal));