Hive

 

About Hive

• Hive is introduced by Facebook.
• It's a data warehouse (data collected from various sources).
• It's functionality is based on SQL.
• It's basically a Query Engine it can also called as database.
• It's an open source framework.
• It's a vehicle than runs on engine(MR).
• It's replacing Java not Map Reduce.
• Basically we are using java in MR to replace the use of that we are using hive.
• The hive has metadata which stores information but not data.
• The hive metadata stores only in RDBMS(Oracle, MySQL) but not the data you insert.
• The data you insert is stored in HDFS.
• In the absence of RDBMS for metadata hive will create an embedded RDBMS called derby.
• The combinations in hive are:
• MYSQL + Hive=Remote Metastore
• Derby + Hive=Embedded Metastore
• The drawback of embedded metastore is data concurrency in clustered system as multiple nodes maybe present.
• By default all hive tables are stored in bin/hadoop fs -ls /user/hive/warehouse
• Without load command also we can move data to hive using put command.
• For load there is MapReduce job but for insert it is.
• HQL(Hive Query Language) which is used for distributed system which provides parallelism.

Few Hive Commands

• create table(sno int,name string) row format delimited fields terminated by ',' lines terminated by '\n' stored as textfile;
• load data local inpath '/user/test.txt' into table test1.table1;
• load data inpath '/user/test.txt' into table test1.table1;
• drop table table1;
• desc table1;
• desc extended table1;