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

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

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> This page describes SQL-based batch ingestion using the [`druid-multi-stage-query`](../multi-stage-query/index.md)
> extension, new in Druid 24.0. Refer to the [ingestion methods](../ingestion/index.md#batch) table to determine which
> ingestion method is right for you.

Apache Druid supports SQL-based ingestion using the bundled [`druid-multi-stage-query` extension](#load-the-extension).
This extension adds a [multi-stage query task engine for SQL](concepts.md#sql-task-engine) that allows running SQL
[INSERT](concepts.md#insert) and [REPLACE](concepts.md#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 SQL task engine, with certain exceptions listed on the [Known
issues](./known-issues.md#select) 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](../development/extensions.md#loading-extensions).

To use [EXTERN](reference.md#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](./concepts.md) to learn more about how SQL-based ingestion and multi-stage queries work.
* [Check out the examples](./examples.md) to see SQL-based ingestion in action.
* [Explore the Query view](../operations/web-console.md) to get started in the web console.