ContextQMD
Back to Druid

SQL-based ingestion

docs/multi-stage-query/index.md

latest3.5 KB
Original Source
<!-- ~ Licensed to the Apache Software Foundation (ASF) under one ~ or more contributor license agreements. See the NOTICE file ~ distributed with this work for additional information ~ regarding copyright ownership. The ASF licenses this file ~ to you under the Apache License, Version 2.0 (the ~ "License"); you may not use this file except in compliance ~ with the License. You may obtain a copy of the License at ~ ~ http://www.apache.org/licenses/LICENSE-2.0 ~ ~ Unless required by applicable law or agreed to in writing, ~ software distributed under the License is distributed on an ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY ~ KIND, either express or implied. See the License for the ~ specific language governing permissions and limitations ~ under the License. -->

This page describes SQL-based batch ingestion using the multi-stage query (MSQ) task engine. Refer to the ingestion methods table to determine which ingestion method is right for you.

Apache® Druid supports SQL-based ingestion using MSQ task engine 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.

External resource types

The MSQ task engine supports reading and writing data from external sources through the EXTERN function.

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. The same is true of any of the input-source specific table function such as S3 or LOCALFILES.

Next steps