Working with PSI Efficiently
Avoid Expensive Methods in PsiElement
PsiElement methods which are expensive with deep trees.
getText() traverses the whole tree under the given element and concatenates strings, consider
getProject() traverse the tree up to the file, which can be long in very nested trees. If you only need PSI element length, use
File and project often can be computed once per some analysis and then stored in fields or passed via parameters.
getTextRange(), etc., all need AST, which can be quite an expensive operation. See below.
Avoid Using Many PSI Trees/Documents
Avoid loading too many parsed trees or documents into memory at the same time. Ideally, only AST nodes from files open in the editor should be present in the memory. Everything else, even if it's needed for resolve/highlighting purposes, can be accessed via PSI interfaces, but its implementations should use stubs underneath, which are less CPU- and memory-expensive.
If stubs don't suit your case well (e.g., the information you need is large and/or very rarely needed, or you're developing a plugin for a language whose PSI you don't control), you can create a custom index or gist.
You can use
AstLoadingFilter in production and
PsiManagerEx.setAssertOnFileLoadingFilter() in tests to ensure you're not loading AST accidentally.
The same applies to documents: only the ones opened in editors should be loaded. Usually, you shouldn't need document contents (as most information can be retrieved from PSI). If you nevertheless need documents, consider saving the information you need to provide in a custom index or gist to get it more cheaply later. If you still need documents, then at least ensure you load them one by one and don't hold them on strong references to let GC free the memory as quickly as possible.
Cache Results of Heavy Computations
multiResolve() and other equivalents), expression types, type inference results, control flow graphs, etc.
CachedValue works well.
If the information you cache depends only on a subtree of the current PSI element (and nothing else: no resolve results or other files), you can cache it in a field in that
PsiElement and drop the cache in an override of
Improving Indexing Performance
Indexing performance metrics in JSON format are generated in logs directory (see sandbox directory for development instance) in 2020.2 and later. These are additionally available in HTML format starting with 2020.1.
Avoid Using AST
Use lexer information instead of parsed trees if possible.
If impossible, use light AST which doesn't create memory-hungry AST nodes inside, so traversing it might be faster. Make sure to traverse only the nodes you need to.
For indexing XML, also consider using
For stub index, implement
LightStubBuilder. For other indexes, you can obtain the light AST manually via
If a custom language contains lazy-parseable elements that never or rarely contain any stubs, consider implementing
StubBuilder.skipChildProcessingWhenBuildingStubs() (preferably using Lexer/node text).
Consider Prebuilt Stubs
If your language has a massive standard library, which is mostly the same for all users, you can avoid stub-indexing it in each installation by providing prebuilt stubs with your distribution. See
Avoiding UI Freezes
Do not Perform Long Operations in UI Thread
In particular, don't traverse VFS, parse PSI, resolve references or query
There are cases when the platform itself invokes such expensive code (e.g., resolve in
AnAction.update()). We're trying to eliminate them. Meanwhile, you can try to speed up what you can in your plugin, it'll be beneficial anyway, as it'll also improve background highlighting performance.
WriteAction s currently have to happen on UI thread, so to speed them up, you can try moving as much as possible out of write action into a preparation step which can be then invoked in background (e.g., using
Don't do anything expensive in event listeners. Ideally, you should only clear some caches. You can also schedule background processing of events, but be prepared that some new events might be delivered before your background processing starts, and thus the world might have changed by that moment or even in the middle of background processing. Consider using
ReadAction.nonBlocking() to mitigate these issues.
Massive batches of VFS events can be pre-processed in background, see
AsyncFileListener (2019.2 or later).