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indexing_and_psi_stubs.md: minor

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topics/basics/indexing_and_psi_stubs.md
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[//]: # (title: Indexing and PSI Stubs)
<!-- Copyright 2000-2020 JetBrains s.r.o. and other contributors. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file. -->
<!-- Copyright 2000-2021 JetBrains s.r.o. and other contributors. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file. -->
## Indices
## Indexes
The indexing framework provides a quick way to locate specific elements, e.g., files containing a certain word or methods with a particular name, in large codebases.
Plugin developers can use the existing indexes built by the IDE itself and build and use their own indexes.
It supports two main types of indexes:
* [File-based indices](file_based_indexes.md)
* [Stub indices](stub_indexes.md)
* [File-based indexes](file_based_indexes.md)
* [Stub indexes](stub_indexes.md)
File-based indexes are built directly over the content of files.
Stub indexes are built over serialized *stub trees*.
@ -20,7 +20,7 @@ Querying a file-based index gets you the set of files matching a specific condit
Querying a stub index gets you the set of matching PSI elements.
Therefore, custom language plugin developers should typically use stub indexes in their plugin implementations.
> [Indices Viewer](https://plugins.jetbrains.com/plugin/13029-indices-viewer/) is a plugin that helps to inspect indices' contents and properties.
> [Index Viewer](https://plugins.jetbrains.com/plugin/13029-index-viewer/) is a plugin that helps to inspect indexes' contents and properties.
Please see also [Improving indexing performance](performance.md#improving-indexing-performance).
>
{type="tip"}
@ -33,19 +33,19 @@ This restriction is managed by [`DumbService`](upsource:///platform/core-api/src
Violations are reported via [`IndexNotReadyException`](upsource:///platform/core-api/src/com/intellij/openapi/project/IndexNotReadyException.java), please see its javadoc on how to adapt callers.
`DumbService` provides API to query whether the IDE is currently in "dumb" mode (where index access is not allowed) or "smart" mode (with all index built and ready to use).
It also provides ways of delaying code execution until indices are ready.
It also provides ways of delaying code execution until indexes are ready.
Please see its JavaDoc for more details.
## Gists
Sometimes, the following conditions hold:
* the aggregation functionality of file-based indices is not needed.
* the aggregation functionality of file-based indexes is not needed.
One just needs to calculate some data based on a particular file's contents and cache it on disk.
* eagerly calculating the data for the entire project during indexing isn't needed (e.g., it slows down the indexing, and/or this data probably will ever be required for a minor subset of all project files).
* the data can be recalculated lazily on request without significant performance penalties.
A file-based index can be used in such cases, but file gists provide a way to perform data calculation lazily, caching on disk, and a more lightweight API.
A [file-based index](file_based_indexes.md) can be used in such cases, but file gists provide a way to perform data calculation lazily, caching on disk, and a more lightweight API.
Please see [`VirtualFileGist`](upsource:///platform/indexing-api/src/com/intellij/util/gist/VirtualFileGist.java) and [`PsiFileGist`](upsource:///platform/indexing-api/src/com/intellij/util/gist/PsiFileGist.java) documentation.
**Example:**