mirror of https://github.com/apache/druid.git
77 lines
3.8 KiB
Markdown
77 lines
3.8 KiB
Markdown
---
|
|
id: update
|
|
title: "Data updates"
|
|
---
|
|
|
|
<!--
|
|
~ 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.
|
|
-->
|
|
|
|
## Overwrite
|
|
|
|
Apache Druid stores data [partitioned by time chunk](../design/architecture.md#datasources-and-segments) and supports
|
|
overwriting existing data using time ranges. Data outside the replacement time range is not touched. Overwriting of
|
|
existing data is done using the same mechanisms as [batch ingestion](../ingestion/index.md#batch).
|
|
|
|
For example:
|
|
|
|
- [Native batch](../ingestion/native-batch.md) with `appendToExisting: false`, and `intervals` set to a specific
|
|
time range, overwrites data for that time range.
|
|
- [SQL `REPLACE <table> OVERWRITE [ALL | WHERE ...]`](../multi-stage-query/reference.md#replace) overwrites data for
|
|
the entire table or for a specified time range.
|
|
|
|
In both cases, Druid's atomic update mechanism ensures that queries will flip seamlessly from the old data to the new
|
|
data on a time-chunk-by-time-chunk basis.
|
|
|
|
Ingestion and overwriting cannot run concurrently for the same time range of the same datasource. While an overwrite job
|
|
is ongoing for a particular time range of a datasource, new ingestions for that time range are queued up. Ingestions for
|
|
other time ranges proceed as normal. Read-only queries also proceed as normal, using the pre-existing version of the
|
|
data.
|
|
|
|
Druid does not support single-record updates by primary key.
|
|
|
|
## Reindex
|
|
|
|
Reindexing is an [overwrite of existing data](#overwrite) where the source of new data is the existing data itself. It
|
|
is used to perform schema changes, repartition data, filter out unwanted data, enrich existing data, and so on. This
|
|
behaves just like any other [overwrite](#overwrite) with regard to atomic updates and locking.
|
|
|
|
With [native batch](../ingestion/native-batch.md), use the [`druid` input
|
|
source](../ingestion/native-batch-input-source.md#druid-input-source). If needed,
|
|
[`transformSpec`](../ingestion/ingestion-spec.md#transformspec) can be used to filter or modify data during the
|
|
reindexing job.
|
|
|
|
With SQL, use [`REPLACE <table> OVERWRITE`](../multi-stage-query/reference.md#replace) with `SELECT ... FROM <table>`.
|
|
(Druid does not have `UPDATE` or `ALTER TABLE` statements.) Any SQL SELECT query can be used to filter,
|
|
modify, or enrich the data during the reindexing job.
|
|
|
|
## Rolled-up datasources
|
|
|
|
Rolled-up datasources can be effectively updated using appends, without rewrites. When you append a row that has an
|
|
identical set of dimensions to an existing row, queries that use aggregation operators automatically combine those two
|
|
rows together at query time.
|
|
|
|
[Compaction](compaction.md) or [automatic compaction](automatic-compaction.md) can be used to physically combine these
|
|
matching rows together later on, by rewriting segments in the background.
|
|
|
|
## Lookups
|
|
|
|
If you have a dimension where values need to be updated frequently, try first using [lookups](../querying/lookups.md). A
|
|
classic use case of lookups is when you have an ID dimension stored in a Druid segment, and want to map the ID dimension to a
|
|
human-readable string that may need to be updated periodically.
|