Detect slow loading of barrel modules #17
Conversation
|
I'm dissatisfied with the output this produces for real traces. |
| @@ -32,6 +32,7 @@ const thresholdDuration = argv.forceMillis * 1000; // microseconds | |||
| const minDuration = argv.skipMillis * 1000; // microseconds | |||
| const minPercentage = 0.6; | |||
| const importExpressionThreshold = 10; | |||
| const sourceFileFanoutThreshold = 5; | |||
There was a problem hiding this comment.
This was for local testing - the real value would be 50+.
| @@ -52,6 +53,7 @@ interface EventSpan { | |||
| start: number; | |||
| end: number; | |||
| children: EventSpan[]; | |||
| droppedChildCount: number; | |||
There was a problem hiding this comment.
Events under minDuration are dropped entirely, making it hard to approximate how many children a findSourceFiles event actually has. This fix was incomplete because the compiler uses sampling to drop short events from the trace before we even get it.
| @@ -157,10 +160,13 @@ async function main(): Promise<void> { | |||
|
|
|||
| const parent = stack[i]; | |||
| const duration = span.end - span.start; | |||
| if (duration >= thresholdDuration || duration >= minPercentage * (parent.end - parent.start)) { | |||
| if (duration >= minDuration && (duration >= thresholdDuration || (span.event?.cat !== "program" && duration >= minPercentage * (parent.end - parent.start)))) { | |||
There was a problem hiding this comment.
I was trying to exclude findSourceFile events from being included simply because they were large percentages of their parents. The parent-child relationship is less important for findSourceFile since eliminating the parent just moves the child to the next event that requires it (think about trying to eliminate a @types/node dependency by cleaning up the first file that pulls it in).
| case "findSourceFile": | ||
| const sourcePath = event.args!.fileName; | ||
| const childCount = curr.children.length + curr.droppedChildCount; | ||
| if (childCount < sourceFileFanoutThreshold || !/node_modules/.test(sourcePath) || /@types\/node/.test(sourcePath)) { |
There was a problem hiding this comment.
In user code, it's definitely uninteresting. @types/node seemed special enough to get an exception too, but it turns out that there are many exceptions - more than true positives, probably.
We've seen some projects slowed down by pulling in a huge number of files from a library when they really only wanted a small portion of the functionality. Ideally, the compiler itself would recognize this but, until then, flagging them could help people make spot fixes. Unfortunately, this seems to have a lot of false positive, esp in monorepos where node_modules might actually be user code.
Part of #2.