Learn everything about HBase

What is HBase?

HBase is non-relational NoSQL distributed and column-oriented database. Here we will have tables and tables have multiple rows and column.HBase provide random real-time read/write access to data.
Here the tables are sorted by row. A table can have multiple columns families. Each column family can have multiple columns.

We can say that in HBase, table is a collection of rows-->row is a collection of multiple column family-->column family is a collection of multiple columns--> column is a collection of multiple key:value pair.

HBase Architecture

HBase has three main parts:
1. HMaster:
HMaster helps to assign region to region servers. The load balancing is done in HBase by assigning regions. Region means vertical cross section of our HBase table. It means that it consists of multiple column family. It also manage the hadoop clusters, create modify and delete tables.
2. Region Server:
Region server means working nodes. So we can say that region servers are the main working nodes. It is used to handle client read, write and modify request. Region server runs on every node. Region server stores actual data on a disk. In region server there is a parts named read cache or block cache. Client read data is stored in read cache or block cache and when the cache is full it removes t the recently used data. There is another cache name memstore. This cache is for perform write operations. Column families has different memstore and this memstore stored the new data which is not stored in the disk.
3. Zookeeper
This is a open source server. Zookeeper maintains the configuration information and distributed synchronization, etc. Zookeeper track HBase all region servers.

Difference between RDBMS and HBase

RDBMS	HBase
This row oriented	This is column oriented
Need to upgrade server to add more processing power, space	Don't need to upgrade the machine to add more processing power, space.
Can't easily add columns	Can easily add columns
Data size depends on disk size of server.	Data size depends on machine numbers.
Only structure data is supported	structure and unstructured data is supported.

HBase shell command

To work with HBase, HBase has a shell.
Let's see some HBase commands:
To start HBase shell type: hbase shell

Command	Description
version	Shows the current version of HBase
status	Used to see the status of HBase
version	Shows the current version of HBase
list	Used to see all the tables
create	Used to create table
list	Used to see all the tables
disable	Used to disable table
enable	Used to enable table
disable	Used to disable table
drop	Used to delete a table from HBase
describe	Used to see description of a table
alter	Used to update a table
drop	Used to delete a table from HBase
drop_all	Used to drop a table by matching condition
put	Used to put a cell value
deleteall	Used to delete all the cells in a given row
get	Used to fetches content from a row or cell
delete	Used to delete a cell value in a table
count	Used to count the number of rows in a table
deleteall	Used to delete all the cells in a given row
scan	Used to show the table data
count	Used to count the number of rows in a table
table_help	Used to see the table related command

How to create table and insert data in table?

To create table, create command is used and here we have to specify the table name and the column family name.
Syntax:
create create '<table_name>',<column_family_name>

Suppose you want to create a student table with student information data and school data column family.
Code:
create 'student','student_information','school_data'

Let's insert data:
To insert put command is used.
Syntax:
put'<table_name>','<row_number>','<column_family:column_name>', '<value>'
Now suppose you want to insert student name in row 2.
Syntax:
put 'student','1','student_information:name','Rafsun'

How to view and read table data?

To view or get table data scan command is used.
Syntax:
scan '<table>'
Suppose you want to view student table.
Syntax:
scan 'student'

Let's read To read get command is used and using get command you can get data of a single row at a time.
Syntax:
get '<table_name>','<row_number>'
You can also get single column.
Syntax:
get '<table_name>','<row_number>',{COLUMN =>'column_family_name:column_name'}

How to disable and enable a table?

How to disable?
If you want to delete a table or want to change a table settings, at first you need to disable the table. To do this disable command is used. If the table is disabled you can't perform scan or insert operation on that table.
Syntax:
disable '<table_name>'
If you want to check a table is disable or not use is_disabled command.
Syntax:
is_disabled '<table_name>'

How enable a table?
To enable a disable table enable command is used.
Syntax:
enable '<table_name>'
If you want to check that is a table is enable or not use is_enable command.
Syntax:
is_enable '<table_name>'

How to do delete operation in HBase table?

To delete a specific cell from a table delete command is used.
Syntax:
delete '<table_name>','<row_number>','<column_family:column_name>','<time_stamp>'
Here time_stamp command is optional

Let's delete a entire row,
Syntax:
deleteall'<table_name>','<row_number>'

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