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51 lines
3.4 KiB
Markdown
51 lines
3.4 KiB
Markdown
---
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title: Indexing and PSI Stubs
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---
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<!-- 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. -->
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## Indices
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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.
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Plugin developers can use the existing indexes built by the IDE itself and build and use their own indexes.
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It supports two main types of indexes:
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* [File-based indices](/basics/indexing_and_psi_stubs/file_based_indexes.md)
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* [Stub indices](/basics/indexing_and_psi_stubs/stub_indexes.md)
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File-based indexes are built directly over the content of files.
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Stub indexes are built over serialized *stub trees*.
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A stub tree for a source file is a subset of its PSI tree, which contains only externally visible declarations and is serialized in a compact binary format.
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Querying a file-based index gets you the set of files matching a specific condition.
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Querying a stub index gets you the set of matching PSI elements.
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Therefore, custom language plugin developers should typically use stub indexes in their plugin implementations.
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> **TIP** [Indices Viewer](https://plugins.jetbrains.com/plugin/13029-indices-viewer/) is a plugin that helps to inspect indices' contents and properties.
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Please see also [Improving indexing performance](/reference_guide/performance/performance.md#improving-indexing-performance).
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## Dumb Mode
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Indexing is a potentially lengthy process.
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It's performed in the background, and during this time, IDE's features are restricted to the ones that don't require index: basic text editing, version control, etc.
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This restriction is managed by [`DumbService`](upsource:///platform/core-api/src/com/intellij/openapi/project/DumbService.java).
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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.
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`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).
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It also provides ways of delaying code execution until indices are ready.
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Please see its JavaDoc for more details.
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## Gists
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Sometimes, the following conditions hold:
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* the aggregation functionality of file-based indices is not needed.
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One just needs to calculate some data based on a particular file's contents and cache it on disk.
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* 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).
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* the data can be recalculated lazily on request without significant performance penalties.
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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.
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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.
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**Example:**
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- [`ImageInfoIndex`](upsource:///images/src/org/intellij/images/index/ImageInfoIndex.java) calculating image dimensions/bit depth needed to be displayed in specific parts of UI. |