Client

Client submits the SQL statements to the Tajo Master to get the result.

Master

Master is the main daemon. It is responsible for query planning and is the coordinator for workers.

Catalog server

Maintains the table and index descriptions. It is embedded in the Master daemon. The catalog server uses Apache Derby as the storage layer and connects via JDBC client.

Worker

Master node assigns task to worker nodes. TajoWorker processes data. As the number of TajoWorkers increases, the processing capacity also increases linearly.

Query Master

Tajo master assigns query to the Query Master. The Query Master is responsible for controlling a distributed execution plan. It launches the TaskRunner and schedules tasks to TaskRunner. The main role of the Query Master is to monitor the running tasks and report them to the Master node.

Node Managers

Manages the resource of the worker node. It decides on allocating requests to the node.

TaskRunner

Acts as a local query execution engine. It is used to run and monitor query process. The TaskRunner processes one task at a time.

It has the following three main attributes −

• Logical plan − An execution block which created the task.
• A fragment − an input path, an offset range, and schema.
• Fetches URIs

Query Executor

It is used to execute a query.

Storage service

Connects the underlying data storage to Tajo.