Overview of Tajo Tables¶

Overview¶

Tablespaces¶

Tablespaces is a physical location where files or data objects representing data rows can be stored. Once defined, a tablespace can be referred to by a name when creating a database or a table. Especially, it is very useful when a Tajo cluster instance should use heterogeneous storage systems such as HDFS, MySQL, and Oracle because each tablespace can be specified to use a different storage system.

Please refer to Tablespaces if you want to know more information about tablespaces.

Managed Table¶

CREATE TABLE statement lets you create a table located in the warehouse directory specified by the configuration property tajo.warehouse.directory or ${tajo.root}/warehouse by default. For example:

CREATE TABLE employee (
 id int,
 name text,
 age
);

External Table¶

CREATE EXTERNAL TABLE statement lets you create a table located in a specify location so that Tajo does not use a default data warehouse location for the table. External tables are in common used if you already have data generated. LOCATION clause must be required for an external table.

CREATE EXTERNAL TABLE employee (
 id int,
 name text,
 age
) LOCATION 'hdfs://table/path';

The location can be a directory located in HDFS, Amazon S3, HBase, or local file system (if a Tajo cluster runs in a single machine). URI examples are as follows:

• HDFS - hdfs://hostname:8020/table1
• Amazon S3 - s3://bucket-name/table1
• local file system - file:///dir/table1
• Openstack Swift - swift://bucket-name/table1

Table Properties¶

All table formats provide parameters for enabling or disabling features and adjusting physical parameters. The WITH clause in the CREATE TABLE statement allows users to set those properties.

The following example is to set a custom field delimiter, NULL character, and compression codec:

CREATE TABLE table1 (
 id int,
 name text,
 score float,
 type text
) USING TEXT WITH('text.delimiter'='\u0001',
                  'text.null'='\\N',
                  'compression.codec'='org.apache.hadoop.io.compress.SnappyCodec');

Each physical table layout has its own specialized properties. They will be addressed in File Formats.

Common Table Properties¶

There are some common table properties which are used in most tables.

CREATE EXTERNAL TABLE table1 (
 t_timestamp  TIMESTAMP,
 t_date    DATE
) USING TEXT WITH('timezone'='ASIA/Seoul') LOCATION '/path-to-table/'