druid/docs/multi-stage-query/index.md

id	title	sidebar_label	description
index	SQL-based ingestion	Overview	Introduces multi-stage query architecture and its task engine

This page describes SQL-based batch ingestion using the druid-multi-stage-query extension, new in Druid 24.0. Refer to the ingestion methods table to determine which ingestion method is right for you.

Apache Druid supports SQL-based ingestion using the bundled druid-multi-stage-query extension. This extension adds a multi-stage query task engine for SQL that allows running SQL INSERT and REPLACE statements as batch tasks. As an experimental feature, the task engine also supports running SELECT queries as batch tasks.

Nearly all SELECT capabilities are available in the multi-stage query (MSQ) task engine, with certain exceptions listed on the Known issues page. This allows great flexibility to apply transformations, filters, JOINs, aggregations, and so on as part of INSERT ... SELECT and REPLACE ... SELECT statements. This also allows in-database transformation: creating new tables based on queries of other tables.

Vocabulary

• Controller: An indexing service task of type query_controller that manages the execution of a query. There is one controller task per query.

• Worker: Indexing service tasks of type query_worker that execute a query. There can be multiple worker tasks per query. Internally, the tasks process items in parallel using their processing pools (up to druid.processing.numThreads of execution parallelism within a worker task).

• Stage: A stage of query execution that is parallelized across worker tasks. Workers exchange data with each other between stages.

• Partition: A slice of data output by worker tasks. In INSERT or REPLACE queries, the partitions of the final stage become Druid segments.

• Shuffle: Workers exchange data between themselves on a per-partition basis in a process called shuffling. During a shuffle, each output partition is sorted by a clustering key.

Load the extension

To add the extension to an existing cluster, add druid-multi-stage-query to druid.extensions.loadlist in your common.runtime.properties file.

For more information about how to load an extension, see Loading extensions.

To use EXTERN, you need READ permission on the resource named "EXTERNAL" of the resource type "EXTERNAL". If you encounter a 403 error when trying to use EXTERN, verify that you have the correct permissions.

Next steps

• Read about key concepts to learn more about how SQL-based ingestion and multi-stage queries work.
• Check out the examples to see SQL-based ingestion in action.
• Explore the Query view to get started in the web console.