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gluxonamcasey
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Set stackTraceLimit to 0 in fileSystemEntryExists
The exception thrown by Node.js's fs.statSync function contains a stack trace that can be expensive to compute. Since this exception isn't used by fileSystemEntryExists, we can safely set Error.stackTraceLimit to 0 without a change in behavior. --- A significant performance improvement was noticed with this change while profiling tsserver on packages within a proprietary monorepo. Specifically, my team saw high self time percentages for Node.js's uvException and handleErrorFromBinding internal functions. These functions are executed within fs.statSync when it fails to find the given path. https://user-images.githubusercontent.com/906558/90183227-220cb800-dd81-11ea-8d61-f41f89481f46.png fs.statSync: https://github.com/nodejs/node/blob/v14.4.0/lib/fs.js#L1030-L1037 handleErrorFromBinding: https://github.com/nodejs/node/blob/v14.4.0/lib/internal/fs/utils.js#L254-L269 uvException: https://github.com/nodejs/node/blob/v14.4.0/lib/internal/errors.js#L390-L443 ## Measurements After adding Error.stackTraceLimit = 0, we saw: - For a large configured project with 12,565 files, tsserver reached the projectLoadingFinish event 48.78% faster. (~46.786s vs ~31.447s) - For a medium project with 7,064 files, tsserver was 25.75% faster. (~20.897s vs ~16.618s) - For a small project with 796 files, tsserver was only a negligible 3.00% faster. (~3.545s vs ~3.442) Measurements were taken on macOS 10.15.6, Node.js 14.4.0, and a recent master commit of TypeScript (610fa28). The average of 3 runs before and after this change were taken. I would normally include .cpuprofile and isolate-*-*-*.log files, but can't post them publicly in this case. If there's any other summaries the TypeScript team would be curious about I can report them. ## fs.statSync Misses Within our monorepo, the fs.statSync misses were mostly searches for alternative file extensions of module imports. - For node_modules imports, a lot of .ts/.tsx lookups failed until the .d.ts file was found. - Within projects with a lot of JSX files, .ts files were looked for before finding the .tsx version. - In the medium scale project mentioned above, a total of 38,515 non-existent files were queried during createProgram.
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src/compiler/sys.ts

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@@ -1662,6 +1662,11 @@ namespace ts {
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}
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function fileSystemEntryExists(path: string, entryKind: FileSystemEntryKind): boolean {
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// Since the error thrown by fs.statSync isn't used, we can avoid collecting a stack trace to improve
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// the CPU time performance.
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const originalStackTraceLimit = Error.stackTraceLimit;
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Error.stackTraceLimit = 0;
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try {
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const stat = _fs.statSync(path);
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switch (entryKind) {
@@ -1673,6 +1678,9 @@ namespace ts {
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catch (e) {
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return false;
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}
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finally {
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Error.stackTraceLimit = originalStackTraceLimit;
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}
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}
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function fileExists(path: string): boolean {

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