High CPU and network usage when working on a network share. 10 seconds delay when pressing F12

[Raukgorth]

Environment data

• Pylance version: 2025.3.2
• OS and version:
  Version: 1.98.2 (system setup)
  Commit: ddc367ed5c8936efe395cffeec279b04ffd7db78
  Date: 2025-03-12T13:32:45.399Z
  Electron: 34.2.0
  ElectronBuildId: 11161602
  Chromium: 132.0.6834.196
  Node.js: 20.18.2
  V8: 13.2.152.36-electron.0
  OS: Windows_NT x64 10.0.19045
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.13.2

Code Snippet

init.py

main.py

import asyncio

async def main():  
  await asyncio.sleep(1)

if __name__ == "__main__":
  asyncio.run(main())
  print("Main task done.")

Repro Steps

1. Create a blank network share on a SMB
2. Start a new project in that share
3. Add a local git repo and commit a change

Expected behavior

4. Minimal CPU and network usage
5. Pylance taking less than 10 seconds when pressing F12

Actual behavior

4. BUG >>> Extensive network traffic and CPU usage
5. BUG >>> Going to declaration in another open file takes about 10 seconds
   XXX

Logs

Full log attached, about 5 megabytes, doesn't fit here
The bit at the end is me disconnecting Ethernet to stop the log as I was unable to copy it.

This is the buggy bit, repeating endlessly:

2025-03-24 13:16:39.222 [info] [Info  - 1:16:39 PM] (14668) Heap stats: total_memory_size=24312MB, total_free_size=12186MB, total_heap_size=137MB, used_heap_size=133MB, cross_worker_used_heap_size=133MB, total_physical_size=137MB, total_available_size=3962MB, heap_size_limit=4096MB
2025-03-24 13:16:39.222 [info] (14668) [BG(1)] indexing: file://bananwypelnionysmietana/bot/main.py [found 2] (0ms)
2025-03-24 13:16:39.222 [info] (14668) Workspace indexing done: file://bananwypelnionysmietana/bot/main.py
2025-03-24 13:16:39.223 [info] (14668) [BG(1)] indexing: file://bananwypelnionysmietana/bot/test.py [found 7] (0ms)
2025-03-24 13:16:39.223 [info] (14668) Workspace indexing done: file://bananwypelnionysmietana/bot/test.py
2025-03-24 13:16:39.683 [info] [Info  - 1:16:39 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\__init__.py'
2025-03-24 13:16:39.695 [info] [Info  - 1:16:39 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\main.py'
2025-03-24 13:16:39.710 [info] [Info  - 1:16:39 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\test.py'
2025-03-24 13:16:39.726 [info] (14668) [BG(1)] indexing: file://bananwypelnionysmietana/bot/__init__.py [found 0] (1ms)
2025-03-24 13:16:39.727 [info] (14668) Workspace indexing done: file://bananwypelnionysmietana/bot/__init__.py
2025-03-24 13:16:39.727 [info] (14668) [BG(1)] indexing: file://bananwypelnionysmietana/bot/main.py [found 2] (0ms)
2025-03-24 13:16:39.727 [info] (14668) Workspace indexing done: file://bananwypelnionysmietana/bot/main.py
2025-03-24 13:16:39.727 [info] (14668) [BG(1)] indexing: file://bananwypelnionysmietana/bot/test.py [found 7] (0ms)
2025-03-24 13:16:39.727 [info] (14668) Workspace indexing done: file://bananwypelnionysmietana/bot/test.py
2025-03-24 13:16:40.187 [info] [Info  - 1:16:40 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\__init__.py'
2025-03-24 13:16:40.199 [info] [Info  - 1:16:40 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\main.py'
2025-03-24 13:16:40.217 [info] [Info  - 1:16:40 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\test.py'
2025-03-24 13:16:40.228 [info] (14668) [BG(1)] indexing: file://bananwypelnionysmietana/bot/__init__.py [found 0] (0ms)
2025-03-24 13:16:40.229 [info] (14668) Workspace indexing done: file://bananwypelnionysmietana/bot/__init__.py
2025-03-24 13:16:40.229 [info] [Info  - 1:16:40 PM] (14668) Heap stats: total_memory_size=24312MB, total_free_size=12159MB, total_heap_size=137MB, used_heap_size=133MB, cross_worker_used_heap_size=133MB, total_physical_size=137MB, total_available_size=3962MB, heap_size_limit=4096MB

pylance.txt

[Raukgorth]

Additional behavior observed:
After few hours of this going on, pylance stops working completely. I have to restart it to get it working again. Please let me know if you need the trace log I will try to get one.

[rchiodo]

This sounds like the root cause of the problem:

2025-03-24 13:16:39.683 [info] [Info  - 1:16:39 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\__init__.py'
2025-03-24 13:16:39.695 [info] [Info  - 1:16:39 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\main.py'
2025-03-24 13:16:39.710 [info] [Info  - 1:16:39 PM] (14668) SourceFile: Received fs event 'change' for path '\\BananWypelnionySmietana\bot\test.py'

Something is firing change events for these files, causing a reindexing.

[Raukgorth]

Without better understanding of SMB and what pylance is doing to the files, to me it seems like scanning the files triggers a change event.

[rchiodo]

Pylance is just reading the files. Those change events are fired by VS code itself. We just listen to them.

This event here:
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#workspace_didChangeWatchedFiles

Something is firing that over and over again.

[rchiodo]

Could be this issue here:
microsoft/vscode#201103

[rchiodo]

This sounds similar as well.
microsoft/vscode#241634

I believe you can disable file change notifications in VS code with this setting:

{
    "files.watcherExclude": {
        "**/path/to/your/smb/shared/folder/**": true
    }
}

For open files, we don't need to watch for changes, so it shouldn't affect Pylance analysis unless you're modifying files on the SMB share from somewhere else.

[Raukgorth]

Hi Rich,

Thanks for looking into this.

The watcher seems to ignore the watcherExclude settings:

[rchiodo]

Ah it seems that's ignored for the workspace. At least according to the API:

https://github.com/microsoft/vscode/blob/f694c69abd029c0fb68f97b9a1e2686afbcbe5cd/src/vscode-dts/vscode.d.ts#L13794

[rchiodo]

Reading it again, not sure why I thought that. It should ignore it. I think you might want to log this bug on VS code then.

Can you turn this on first?

"python.trace.server": "compact"

That will log the LSP messages that VS code sends us. That will verify those file change events are coming from VS code.