CSE 6250 Big Data for Healthcare

Hadoop HBase

TIP

  • Know HBase interactive shell.
  • Being able to conduct CRUD operations.

Apache HBase is a distributed column-oriented database built on top of the Hadoop file system. Use HBase when you need random, realtime read/write access to your Big Data. It provides a convenient interactive shell as well as a Java API.

Interactive Shell

You can start the HBase interactive shell using the command hbase shell. After entering this command, you will see the following output:

HBase Shell; enter 'help<RETURN>' for list of supported commands.
Type "exit<RETURN>" to leave the HBase Shell
Version 0.94.18, rb149f3f0d25c5cd2f195b39fe05d42507fdeabfc, Sat May 23 00:09:16 GMT 2015

hbase(main):001:0>

To exit the interactive shell, type exit or <ctrl+c>.

Create

The syntax to create a table from an HBase shell is shown below.

create 'table name', 'column family'

Note that in the HBase data model columns are grouped into "column families", which must be defined up front during table creation. These column families are stored together on disk. Because of this HBase is consided a column-oriented data store.

Let's create a table called hospital with two column families: id and value.

hbase(main):002:0> create 'hospital', 'id', 'value'

And it will give you the following output.

0 row(s) in 1.9850 seconds

=> Hbase::Table - hospital

Update

List table(s)

hbase(main):003:0> list
TABLE
hospital
1 row(s) in 0.0180 seconds

Describe and alter table

The describe command returns the description of the table.

hbase(main):004:0> describe 'hospital'
'hospital', {NAME => 'id', DATA_BLOCK_ENCODING => 'NONE', BLOOMFILTER => 'NONE', REPLICATION_SCOPE => true
  '0', VERSIONS => '3', COMPRESSION => 'NONE', MIN_VERSIONS => '0', TTL => '2147483647', KEEP_DELETED_
 CELLS => 'false', BLOCKSIZE => '65536', IN_MEMORY => 'false', ENCODE_ON_DISK => 'true', BLOCKCACHE =>
  'true'}, {NAME => 'value', DATA_BLOCK_ENCODING => 'NONE', BLOOMFILTER => 'NONE', REPLICATION_SCOPE =
 > '0', VERSIONS => '3', COMPRESSION => 'NONE', MIN_VERSIONS => '0', TTL => '2147483647', KEEP_DELETED
 _CELLS => 'false', BLOCKSIZE => '65536', IN_MEMORY => 'false', ENCODE_ON_DISK => 'true', BLOCKCACHE =
 > 'true'}
1 row(s) in 0.0350 seconds

This shows some basic information for each column family. For example, the id column family has block size of 65536 and keeps at most 3 versions for each cell (distinguishable by timestamp).

We can alter the the table settings by using alter. But first we must disable the table.

hbase(main):005:0> disable 'hospital'
hbase(main):006:0> alter 'hospital', {NAME => 'id', VERSIONS => 5}

Don't forget to re-enable after changing the setting.

hbase(main):007:0> enable 'hospital'

Put data

Using the put command, you can insert rows into a table. The syntax is as follows:

put 'table name', 'row key', 'colfamily:colname', 'value'

For example, let's put a patient-id record.

hbase(main):008:0> put 'hospital', 'row1', 'id:patient', 'patient-id-1'
0 row(s) in 0.0140 seconds

This puts the value patient-id-1 in row row1 and column patient (within the column family id). Let's put some more records.

hbase(main):009:0> put 'hospital', 'row1', 'id:event', 'event-id-1'
hbase(main):010:0> put 'hospital', 'row1', 'value:value', '1'
hbase(main):011:0> put 'hospital', 'row2', 'id:event', 'event-id-2'

Read

Cluster status

To check the status of the cluster use the status command:

hbase(main):001:0> status
(may have some debug messages)
2 servers, 0 dead, 1.0000 average load

Table data

Using the scan command, you can view the table data.

hbase(main):012:0> scan 'hospital'
ROW            COLUMN+CELL
 row1          column=id:event, timestamp=1436623001980, value=event-id-1
 row1          column=id:patient, timestamp=1436622532169, value=patient-id-1
 row1          column=value:value, timestamp=1436622642925, value=1
 row2          column=id:event, timestamp=1436623003694, value=event-id-2
2 row(s) in 0.0130 seconds

If you only want to know the number of rows in a table, you can use:

hbase(main):013:0> count 'hospital'
2 row(s) in 0.0130 seconds

The get command can be used to retrieve a single row of data at a time.

hbase(main):014:0> get 'hospital', 'row1' 
COLUMN                                   CELL
 id:event           timestamp=1436623001980, value=event-id-1
 id:patient         timestamp=1436622532169, value=patient-id-1
 value:value        timestamp=1436622642925, value=1
3 row(s) in 0.0270 seconds

To retrieve the data in a particular column within a row we can use the following syntax:

hbase(main):015:0> get 'hospital', 'row1', {COLUMN => 'id:patient'}
 id:patient       timestamp=1436622532169, value=patient-id-1
 1 row(s) in 0.9730 seconds

Delete

Delete cell

You can delete a specific cell in a table by using the delete command

hbase(main):016:0> delete 'hospital', 'row1', 'id:event'
0 row(s) in 0.0100 seconds

To delete all the cells in a row, use the deleteall command

hbase(main):017:0> deleteall 'hospital', 'row1'
0 row(s) in 0.0110 seconds

Drop table

Using the drop command, you can delete a table. Before dropping a table, you must disable it.

hbase(main):018:0> disable 'hospital'
0 row(s) in 1.1000 seconds

hbase(main):019:0> drop 'hospital'

← Hadoop Streaming →