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# QueryEngine

<img style="width:100%; max-width:800px; max-height:600px; margin-left:auto; margin-right:auto; display:block;" src="https://user-images.githubusercontent.com/19167280/73625242-f648a100-467e-11ea-921c-b954a3ecae7a.png">

## Design ideas

The query engine is responsible for parsing all user commands, generating plans, delivering them to the corresponding executors, and returning result sets.

## Related classes

* org.apache.iotdb.db.service.TSServiceImpl

  IoTDB server-side RPC implementation, which directly interacts with the client.

* org.apache.iotdb.db.qp.Planner

  Parse SQL, generate logical plans, optimize logical plans, and generate physical plans.

* org.apache.iotdb.db.qp.executor.PlanExecutor

  Distribute the physical plan to the corresponding actuators, including the following four specific actuators.

  * MManager: Metadata operations
  * StorageEngine: Data write
  * QueryRouter: Data query
  * LocalFileAuthorizer: Permission operation

* org.apache.iotdb.db.query.dataset.*

  The batch result set is returned to the client and contains part of the query logic.

## Query process

* SQL parsing
* Generate logical plans
* Generate physical plans
* Constructing a result set generator
* Returning result sets in batches

## Related documents

* [Query Plan Generator](/SystemDesign/QueryEngine/Planner.html)
* [PlanExecutor](/SystemDesign/QueryEngine/PlanExecutor.html)
