What is the best tool for creating workflow or chaining jobs in hadoop ?

Sometimes we require some tools to chain mapreduce jobs, hive jobs, pig jobs etc. We can chain these jobs using our own way either by using programs or using some scripts. But the best way to chain jobs in hadoop ecosystem is by using oozie.

Oozie is a workflow and orchestration framework in hadoop ecosystem. We don't need to worry about the complexities of handling various scenarios that may have to be considered while developing a chaining tool. Oozie is a very simple tool and the workflows can be achieved by using an xml file. For more details refer oozie website

How to pass small number of configuration parameters to a mapper and reducer ?

Hadoop is having several configurable properties that will be present in several xml and properties files. The main configuration files in hadoop are core-site.xml, mapred-site.xml, hdfs-site.xml, yarn-site.xml. The parameters in these configuration files are set while installing the cluster. This will be done by the administrator.

If a developer while developing the mapreduce programs want to modify some of the configuration parameter, he can do it from the program itself. The way to modify these values from the program is by instantiating the configuration class and setting the configuration values by passing the parameter and value as key-value pairs to the program.

The syntax is as shown below
Configuration conf = new Configuration();
conf.set("key1","value1");
conf.set("key2","value2");