org.apache.hadoop.mapreduce.lib.db
Class TextSplitter

java.lang.Object
  extended by org.apache.hadoop.mapreduce.lib.db.BigDecimalSplitter
      extended by org.apache.hadoop.mapreduce.lib.db.TextSplitter
All Implemented Interfaces:
DBSplitter

@InterfaceAudience.Public
@InterfaceStability.Evolving
public class TextSplitter
extends BigDecimalSplitter

Implement DBSplitter over text strings.


Constructor Summary
TextSplitter()
           
 
Method Summary
 List<InputSplit> split(Configuration conf, ResultSet results, String colName)
          This method needs to determine the splits between two user-provided strings.
 
Methods inherited from class org.apache.hadoop.mapreduce.lib.db.BigDecimalSplitter
tryDivide
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

TextSplitter

public TextSplitter()
Method Detail

split

public List<InputSplit> split(Configuration conf,
                              ResultSet results,
                              String colName)
                       throws SQLException
This method needs to determine the splits between two user-provided strings. In the case where the user's strings are 'A' and 'Z', this is not hard; we could create two splits from ['A', 'M') and ['M', 'Z'], 26 splits for strings beginning with each letter, etc. If a user has provided us with the strings "Ham" and "Haze", however, we need to create splits that differ in the third letter. The algorithm used is as follows: Since there are 2**16 unicode characters, we interpret characters as digits in base 65536. Given a string 's' containing characters s_0, s_1 .. s_n, we interpret the string as the number: 0.s_0 s_1 s_2.. s_n in base 65536. Having mapped the low and high strings into floating-point values, we then use the BigDecimalSplitter to establish the even split points, then map the resulting floating point values back into strings.

Specified by:
split in interface DBSplitter
Overrides:
split in class BigDecimalSplitter
Throws:
SQLException


Copyright © 2012 Apache Software Foundation. All Rights Reserved.