docs(cpp/faq): Add RAM disk usage instructions for IntelliSense cache (ipch) - #8859

@microsoft-github-policy-service agree

Alexandra Kemper (@AlexandraKemperMS) Can you review this PR?

The issue microsoft/vscode-cpptools#13890 also mentions the browse database, e.g. C_Cpp.default.browse.databaseFilename.

This doesn't seem like a good use of memory to me. I think it would be a better to use the memory for the IntelliSense processes themselves (which memory map the ipch files, so by having the ipch files in memory you're essentially using twice as much memory). Users who are concerned with ipch writing should set C_Cpp.intelliSenseCacheSize to 0. If the cache is using memory, then it'll cause few IntelliSense processes to be available in memory.

Do you have any data or performance data for scenarios where this actually improves performance?

...well, it would improve performance if you had a set of files that were frequently opened/closed causing the IntelliSense process to shutdown/restart frequently...but the user might be better off just keeping the files open (keep the cpptools-srv process running).

The comment Improves IntelliSense responsiveness for large projects. is not valid because the IntelliSense cache only stores information on a single TU's headers which is not directly related to the size of a project -- the comment would be valid if applied to the browse database (C_Cpp.default.browse.databaseFilename), which is larger for larger projects. A small project could still use large ipch files (i.e. including data on system/external headers).

Thanks for the feedback, Sean McManus (@sean-mcmanus) . I’ve updated the FAQ:

• Removed the performance claim and clarified that a RAM disk does not generally improve IntelliSense performance and may increase memory usage because ipch files are memory-mapped.
• Emphasized the primary use case as minimizing SSD writes.
• Added a tip to set "C_Cpp.intelliSenseCacheSize": 0 to disable the cache entirely if avoiding disk writes is the goal.
• Added a Related note pointing to C_Cpp.default.browse.databaseFilename as the location of the browse database (larger for bigger projects), without recommending RAM disk for it.

can you review my PR??

can you review my PR??

I think our team might be busy right now. I might be able to review it later.

can you now review my PR??

Sean McManus (@sean-mcmanus) I discussed this with Alexandra Kemper (@AlexandraKemperMS) and because this is a very specific use case, she suggested to include this in the wiki over here: https://github.com/microsoft/vscode-cpptools/wiki/Optimizing-your-configuration

WDYT?

Sean McManus (@sean-mcmanus) can you check??

The wiki seems good to me.

Nick Trogh (@ntrogh) can you merge my PR now??

Devank Gupta (@Devankguptaa) The decision was to include this guidance in the wiki (https://github.com/microsoft/vscode-cpptools/wiki/Optimizing-your-configuration) and not in the C++ docs.

I'll close this PR - can you create a request in the microsoft/vscode-cpptools repo?

Hi Nick Trogh (@ntrogh) 👋
I’m not able to fork the microsoft/vscode-cpptools.wiki repository on GitHub.
Could you please guide me on how to proceed with contributing the changes?

Sean McManus (@sean-mcmanus) Can you provide guidance on how to best proceed? Should Devank Gupta (@Devankguptaa) file an issue with the wiki updates?

Alexandra Kemper (@AlexandraKemperMS) Nick Trogh (@ntrogh) I don't think users can create a PR to update the Wiki? Or I could be mistaken...it might be possible via git clone https://github.com/microsoft/vscode-cpptools.wiki.git? I haven't tried.

Sean McManus (@sean-mcmanus) I suggest creating an issue and providing the details for updating the wiki in there.

Sean McManus (@sean-mcmanus) can you raise the issue?

Devank Gupta (@Devankguptaa) microsoft/vscode-cpptools#13991

Sean McManus (@sean-mcmanus) should I have to raise the PR again or it will be automatically merged?

Sean McManus (@sean-mcmanus) should I have to raise the PR again or it will be automatically merged?

Devank Gupta (@Devankguptaa) Merged where? To the wiki?

Sean McManus (@sean-mcmanus) Yes to the wiki

Devank Gupta (@Devankguptaa) We can add it to the wiki page after someone reviews it.