BIGDATA

Checking XML Validity When you edit XML, it is a good idea to use an XML-aware editor to be sure that your syntax is correct and your XML is well-formed. You can also use the xmllint utility to check that your XML is well-formed. By default, xmllint re-flows and prints the XML to standard output. To check for well-formedness and only print output if errors exist, use the command xmllint -noout filename.xml .

The HQuorumPeer process is a ZooKeeper instance which is controlled and started by HBase. If you use ZooKeeper this way, it is limited to one instance per cluster node, , and is appropriate for testing only. If ZooKeeper is run outside of HBase, the process is called QuorumPeer 

Seq No Deprecated API NEW API 1 Release 0.20 Release 1.X and 2.X 2 Interfaces (means you can add a method with default implementation to an abstract class without breaking old implementations of class Abstract classes For Example Mapper and Reducer interfaces in Old API are abstract classes in new API 3 Package org.apache.hadoop.mapred org.apache.hadoop.mapreduce 4 JobConf,the OutputCollector and the Reporter Context Object   (allows the user code to communicate with MapReduce System) 5 Both API’s, Key-Value record pairs are pushed to mapper and reducer In addition execution flow can be controlled by run() method 6 Job Control by JobClient class Job class 7 Output file are named as Part-nnnnn Part-m-nnnnn( mapper) , part-r-nnnnn(reducer) 8 ...