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HDFS

       Hadoop Introduction

       Getting Started with HDFS

       Features of HDFS

       How exactly Data is Stored on HDFS Cluster?

       Hadoop Architecture

       Replication 

       SafeMode

       Configuration Files

       Namenode, Secondary Namenode and Datanodes

       Heart Beat Mechanism

       Hadoop CLI Commands 

 

MapReduce

       MapReduce Introduction

       Phases of MapReduce

 

Apache PIG

       PIG Introduction

       Execution Modes of PIG 

       Differences between MapReduce and PIG

HIVE

        Hive Introduction

        Hive Tables

        Hive Metastore

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Hive Metastore

Metastore is the internal database for Hive, it is the central repository of Hive Metadata. In this Metastore all the tables information, tables schema, column information, partitioning information will get stored. By default Hive will come up with Derby database as its Metastore. As the default Metastore is Derby, we need not to configure the same, if we want to change the database then we must configure explicitly. 

If we want to configure the Hive Metastore explicitly(other than Derby), we can do so in "hive-site.xml". As part of Metastore configuration there are two parts: 

• Setting of Connection Url
• Setting of Driver name for the same 

The following figure shows you the configuration details. 
 

Configuration of HIVE Metastore

           

Hive Tables

As of now we have seen Hive Introduction. We know that HIVE is used to pose queries on the processed data. Generally in RDBMS we pose queries on Tables. Hive also stores the data in the form of Tables, these tables are stored on HDFS. The following are the two types of tables in HIVE.

• Managed Tables
• External Tables

Hive also stores the metadata of these tables in Hive Metastore. In this post let us see in detail about how to create a table, and how to import data into them.

Managed Tables: 

As the name implies, these tables are managed by Hive Warehouse system. All the Managed tables will be stored in the sub-directories of Hive Warehouse directory. The following is the command tothe Managed Tables.

Managed Table Creation

The following is the example of Managed tables:

Managed table example

External Tables:

As the name implies these are not managed by Warehouse. All the external tabular data is stored in the location specified in the at the time of creation. The following is the syntax to create the External tables. 

External Table Syntax

If we don't specify the HDFS location or external keyword in the command, it will create a Managed table instead of External table. The following is the example of external table. 

External Table Example