August 12, 2022 · 14 min · 2926 words · Jeffrey Ochoa
Table of Contents
We can interact with HBase in two ways,
HBase interactive shell mode and
Through Java API
In HBase, interactive shell mode is used to interact with HBase for table operations, table management, and data modeling. By using Java API model, we can perform all type of table and data operations in HBase. We can interact with HBase using this both methods.
The only difference between these two is Java API use java code to connect with HBase and shell mode use shell commands to connect with HBase.
Quick overcap of HBase before we proceed-
HBase uses Hadoop files as storage system to store the large amounts of data. Hbase consists of Master Servers and Regions Servers
The data that is going to store in HBase will be in the form of regions. Further, these regions will be split up and stored in multiple region servers
This shell commands allows the programmer to define table schemas and data operations using complete shell mode interaction
Whichever command we use, it’s going to reflect in HBase data model
We use HBase shell commands in operating system script interpreters like Bash shell
Bash shell is the default command interpreters for most of Linux and Unix operating distributions
HBase advanced versions provides shell commands jruby-style object oriented references for tables
Table reference variables can be used to perform data operations in HBase shell mode
For examples,
In this tutorial, we have created a table in which ‘education’ represents table name and corresponds to column name “guru99”.
In some commands “guru99,” itself represents a table name.
In this tutorial- you will learn,
General commands
Tables Managements commands
Data manipulation commands
Cluster Replication Commands
In Hbase, general commands are categorized into following commands
Status
Version
Table_help ( scan, drop, get, put, disable, etc.)
Whoami
To get enter into HBase shell command, first of all, we have to execute the code as mentioned below
hbase Shell
Once we get to enter into HBase shell, we can execute all shell commands mentioned below. With the help of these commands, we can perform all type of table operations in the HBase shell mode.
Let us look into all of these commands and their usage one by one with an example.
This command will give details about the system status like a number of servers present in the cluster, active server count, and average load value. You can also pass any particular parameters depending on how detailed status you want to know about the system. The parameters can be ‘summary’, ‘simple’, or ‘detailed’, the default parameter provided is “summary”.
Below we have shown how you can pass different parameters to the status command.
If we observe the below screen shot, we will get a better idea.
hbase(main):001:0>status
hbase(main):002:0>status ‘simple’
hbase(main):003:0>status ‘summary’
hbase(main):004:0> status ‘detailed’
When we execute this command status, it will give information about number of server’s present, dead servers and average load of server, here in screenshot it shows the information like- 1 live server, 1 dead servers, and 7.0000 average load.
What and how to use table-referenced commands
It will provide different HBase shell command usages and its syntaxes
Here in the screen shot above, its shows the syntax to “create” and “get_table” command with its usage. We can manipulate the table via these commands once the table gets created in HBase.
It will give table manipulations commands like put, get and all other commands information.
In HBase, Column families can be set to time values in seconds using TTL. HBase will automatically delete rows once the expiration time is reached. This attribute applies to all versions of a row – even the current version too.
The TTL time encoded in the HBase for the row is specified in UTC. This attribute used with table management commands.
Important differences between TTL handling and Column family TTLs are below
Cell TTLs are expressed in units of milliseconds instead of seconds.
A cell TTLs cannot extend the effective lifetime of a cell beyond a Column Family level TTL setting.
The above example explains how to create a table in HBase with the specified name given according to the dictionary or specifications as per column family. In addition to this we can also pass some table-scope attributes as well into it.
In order to check whether the table ‘education’ is created or not, we have to use the “list” command as mentioned below.
“List” command will display all the tables that are present or created in HBase
The output showing in above screen shot is currently showing the existing tables in HBase
Here in this screenshot, it shows that there are total 8 tables present inside HBase
We can filter output values from tables by passing optional regular expression parameters
It will give more information about column families present in the mentioned table
In our case, it gives the description about table “education.”
It will give information about table name with column families, associated filters, versions and some more details.
This command will disable all the tables matching the given regex.
The implementation is same as delete command (Except adding regex for matching)
Once the table gets disable the user can able to delete the table from HBase
Before delete or dropping table, it should be disabled first
This command will start enabling the named table
Whichever table is disabled, to retrieve back to its previous state we use this command
If a table is disabled in the first instance and not deleted or dropped, and if we want to re-use the disabled table then we have to enable it by using this command.
Here in the above screenshot we are enabling the table “education.”
To delete the table present in HBase, first we have to disable it
To drop the table present in HBase, first we have to disable it
So either table to drop or delete first the table should be disable using disable command
Here in above screenshot we are dropping table “education.”
Before execution of this command, it is necessary that you disable table “education.”
This command will drop all the tables matching the given regex
Tables have to disable first before executing this command using disable_all
Tables with regex matching expressions are going to drop from HBase
This command will verify whether the named table is enabled or not. Usually, there is a little confusion between “enable” and “is_enabled” command action, which we clear here
Suppose a table is disabled, to use that table we have to enable it by using enable command
is_enabled command will check either the table is enabled or not
This command alters the column family schema. To understand what exactly it does, we have explained it here with an example.
Examples:
In these examples, we are going to perform alter command operations on tables and on its columns. We will perform operations like
Altering single, multiple column family names
Deleting column family names from table
Several other operations using scope attributes with table
To change or add the ‘guru99_1’ column family in table ‘education’ from current value to keep a maximum of 5 cell VERSIONS,
“education” is table name created with column name “guru99” previously
Here with the help of an alter command we are trying to change the column family schema to guru99_1 from guru99
hbase> alter ’education’, NAME=‘guru99_1’, VERSIONS=>5
You can also operate the alter command on several column families as well. For example, we will define two new column to our existing table “education”.
We can change more than one column schemas at a time using this command
guru99_2 and guru99_3 as shown in above screenshot are the two new column names that we have defined for the table education
We can see the way of using this command in the previous screen shot
In this step, we will see how to delete column family from the table. To delete the ‘f1’ column family in table ‘education’.
Use one ofthese commands below,
hbase> alter ’education’, NAME => ‘f1’, METHOD => ‘delete’
hbase> alter ’education’, ‘delete’ =>’ guru99_1’
In this command, we are trying to delete the column space name guru99_1 that we previously created in the first step
As shown in the below screen shots, it shows two steps – how to change table scope attribute and how to remove the table scope attribute.
Syntax: alter <‘tablename’>, MAX_FILESIZE=>‘132545224’
Step 1) You can change table-scope attributes like MAX_FILESIZE, READONLY, MEMSTORE_FLUSHSIZE, DEFERRED_LOG_FLUSH, etc. These can be put at the end;for example, to change the max size of a region to 128MB or any other memory value we use this command.
Usage:
We can use MAX_FILESIZE with the table as scope attribute as above
The number represent in MAX_FILESIZE is in term of memory in bytes
NOTE: MAX_FILESIZE Attribute Table scope will be determined by some attributes present in the HBase. MAX_FILESIZE also come under table scope attributes.
Step 2) You can also remove a table-scope attribute using table_att_unset method. If you see the command
alter ’education’, METHOD => ’table_att_unset’, NAME => ‘MAX_FILESIZE’
The above screen shot shows altered table name with scope attributes
Method table_att_unset is used to unset attributes present in the table
The second instance we are unsetting attribute MAX_FILESIZE
After execution of the command, it will simply unset MAX_FILESIZE attribute from”education” table.
Through this command, you can get the status of the alter command
Which indicates the number of regions of the table that have received the updated schema pass table name
Here in above screen shot it shows 1/1 regions updated. It means that it has updated one region. After that if it successful it will display comment done.
These commands will work on the table related to data manipulations such as putting data into a table, retrieving data from a table and deleting schema, etc.
The commands come under these are
Count
Put
Get
Delete
Delete all
Truncate
Scan
Let look into these commands usage with an example.
The command will retrieve the count of a number of rows in a table. The value returned by this one is the number of rows.
Current count is shown per every 1000 rows by default.
Count interval may be optionally specified.
Default cache size is 10 rows.
Count command will work fast when it is configured with right Cache.
Example:
hbase> count ‘guru99’, CACHE=>1000
This example count fetches 1000 rows at a time from “Guru99” table.
We can make cache to some lower value if the table consists of more rows.
But by default it will fetch one row at a time.
Syntax: put <‘tablename’>,<‘rowname’>,<‘columnvalue’>,<‘value’>
This command is used for following things
It will put a cell ‘value’ at defined or specified table or row or column.
It will optionally coordinate time stamp.
Example:
Here we are placing values into table “guru99” under row r1 and column c1
hbase> put ‘guru99’, ‘r1’, ‘c1’, ‘value’, 10
We have placed three values, 10,15 and 30 in table “guru99” as shown in screenshot below
Suppose if the table “Guru99” having some table reference like say g. We can also run the command on table reference also like
hbase> g.put ‘guru99’, ‘r1’, ‘c1’, ‘value’, 10
The output will be as shown in the above screen shot after placing values into “guru99”.
To check whether the input value is correctly inserted into the table, we use “scan” command. In the below screen shot, we can see the values are inserted correctly
Code Snippet: For Practice
create ‘guru99’, {NAME=>‘Edu’, VERSIONS=>213423443}
put ‘guru99’, ‘r1’, ‘Edu:c1’, ‘value’, 10
put ‘guru99’, ‘r1’, ‘Edu:c1’, ‘value’, 15
put ‘guru99’, ‘r1’, ‘Edu:c1’, ‘value’, 30
From the code snippet, we are doing these things
Here we are creating a table named ‘guru99’ with the column name as “Edu.”
By using “put” command, we are placing values into row name r1 in column “Edu” into table “guru99.”
Syntax: get <‘tablename’>, <‘rowname’>, {< Additional parameters>}
Here include TIMERANGE, TIMESTAMP, VERSIONS and FILTERS.
By using this command, you will get a row or cell contents present in the table. In addition to that you can also add additional parameters to it like TIMESTAMP, TIMERANGE,VERSIONS, FILTERS, etc. to get a particular row or cell content.
Examples:-
hbase> get ‘guru99’, ‘r1’, {COLUMN => ‘c1’}
For table “guru99′ row r1 and column c1 values will display using this command as shown in the above screen shot
hbase> get ‘guru99’, ‘r1’
For table “guru99″row r1 values will be displayed using this command
hbase> get ‘guru99’, ‘r1’, {TIMERANGE => [ts1, ts2]}
For table “guru99″row 1 values in the time range ts1 and ts2 will be displayed using this command
hbase> get ‘guru99’, ‘r1’, {COLUMN => [‘c1’, ‘c2’, ‘c3’]}
For table “guru99” row r1 and column families’ c1, c2, c3 values will be displayed using this command
This command will delete cell value at defined table of row or column.
Delete must and should match the deleted cells coordinates exactly.
When scanning, delete cell suppresses older versions of values.
Example:
hbase(main):)020:0> delete ‘guru99’, ‘r1’, ‘c1’’.
The above execution will delete row r1 from column family c1 in table “guru99.”
Suppose if the table “guru99” having some table reference like say g.
We can run the command on table reference also like hbase> g.delete ‘guru99’, ‘r1’, ‘c1′”.
This command scans entire table and displays the table contents.
We can pass several optional specifications to this scan command to get more information about the tables present in the system.
Scanner specifications may include one or more of the following attributes.
These are TIMERANGE, FILTER, TIMESTAMP, LIMIT, MAXLENGTH, COLUMNS, CACHE, STARTROW and STOPROW.
scan ‘guru99’
The output as below shown in screen shot
In the above screen shot
It shows “guru99” table with column name and values
It consists of three row values r1, r2, r3 for single column value c1
It displays the values associated with rows
Examples:-
The different usages of scan command
Code Example: First create table and place values into table
create ‘guru99’, {NAME=>‘e’, VERSIONS=>2147483647}
put ‘guru99’, ‘r1’, ’e:c1’, ‘value’, 10
put ‘guru99’, ‘r1’, ’e:c1’, ‘value’, 12
put ‘guru99’, ‘r1’, ’e:c1’, ‘value’, 14
delete ‘guru99’, ‘r1’, ’e:c1’, 11
Input Screenshot:
If we run scan command
Query: scan ‘guru99’, {RAW=>true, VERSIONS=>1000}
It will display output shown in below.
Output screen shot:
The output shown in above screen shot gives the following information
Scanning guru99 table with attributes RAW=>true, VERSIONS=>1000
Displaying rows with column families and values
In the third row, the values displayed shows deleted value present in the column
The output displayed by it is random; it cannot be same order as the values that we inserted in the table
These commands work on cluster set up mode of HBase.
For adding and removing peers to cluster and to start and stop replication these commands are used in general.
HBase shell and general commands give complete information about different type of data manipulation, table management, and cluster replication commands. We can perform various functions using these commands on tables present in HBase.
hbase> remove_peer ‘1’
