程序包 org.apache.hadoop.mapred.lib.db

org.apache.hadoop.mapred.lib.db Package This package contains a library to read records from a database as an input to a mapreduce job, and write the output records to the database.

请参阅: 说明

接口概要

接口	说明
DBWritable	Objects that are read from/written to a database should implement DBWritable.

类概要

类	说明
DBConfiguration	A container for configuration property names for jobs with DB input/output.
DBInputFormat<T extends DBWritable>	A InputFormat that reads input data from an SQL table.
DBInputFormat.DBInputSplit	A InputSplit that spans a set of rows
DBInputFormat.NullDBWritable	A Class that does nothing, implementing DBWritable
DBOutputFormat<K extends DBWritable,V>	A OutputFormat that sends the reduce output to a SQL table.

程序包org.apache.hadoop.mapred.lib.db的说明

org.apache.hadoop.mapred.lib.db Package

This package contains a library to read records from a database as an input to a mapreduce job, and write the output records to the database.

The Database to access can be configured using the static methods in the DBConfiguration class. Jobs reading input from a database should use DBInputFormat#setInput() to set the configuration. And jobs writing its output to the database should use DBOutputFormat#setOutput().

Tuples from/to the database are converted to/from Java objects using DBWritable methods. Typically, for each table in the db, a class extending DBWritable is defined, which holds the fields of the tuple. The fields of a record are read from the database using DBWritable#readFields(ResultSet), and written to the database using DBWritable#write(PreparedStatament statement).

An example program using both DBInputFormat and DBOutputFormat can be found at src/examples/org/apache/hadoop/examples/DBCountPageview.java.