mirror of https://github.com/apache/druid.git
40 lines
1.8 KiB
Markdown
40 lines
1.8 KiB
Markdown
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---
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id: schema-changes
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title: "Schema changes"
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---
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<!--
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~ Licensed to the Apache Software Foundation (ASF) under one
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~ or more contributor license agreements. See the NOTICE file
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~ distributed with this work for additional information
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~ regarding copyright ownership. The ASF licenses this file
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~ to you under the Apache License, Version 2.0 (the
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~ "License"); you may not use this file except in compliance
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~ with the License. You may obtain a copy of the License at
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~
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~ http://www.apache.org/licenses/LICENSE-2.0
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~
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~ Unless required by applicable law or agreed to in writing,
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~ software distributed under the License is distributed on an
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~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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~ KIND, either express or implied. See the License for the
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~ specific language governing permissions and limitations
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~ under the License.
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-->
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## For new data
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Apache Druid allows you to provide a new schema for new data without the need to update the schema of any existing data.
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It is sufficient to update your supervisor spec, if using [streaming ingestion](../ingestion/index.md#streaming), or to
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provide the new schema the next time you do a [batch ingestion](../ingestion/index.md#batch). This is made possible by
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the fact that each [segment](../design/architecture.md#datasources-and-segments), at the time it is created, stores a
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copy of its own schema. Druid reconciles all of these individual segment schemas automatically at query time.
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## For existing data
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Schema changes are sometimes necessary for existing data. For example, you may want to change the type of a column in
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previously-ingested data, or drop a column entirely. Druid handles this using [reindexing](update.md), the same method
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it uses to handle updates of existing data. Reindexing involves rewriting all affected segments and can be a
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time-consuming operation.
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