Significant delay in initialization for completion/navigation on open file

[ljpsevenc]

I use vscode with clangd extension for code completion and navigation, but when I open or reopen a file, it takes a very long time, about 30~60s, for clangd to initialize. The log of the clangd extension is like below:
I[11:32:54.655] <-- textDocument/hover(2699)
I[11:32:54.782] <-- $/cancelRequest
I[11:33:26.077] --> workspace/semanticTokens/refresh(53)
I[11:33:26.077] --> textDocument/clangd.fileStatus
I[11:33:26.080] <-- reply(53)
I[11:33:28.536] --> textDocument/publishDiagnostics
I[11:33:28.556] --> reply:textDocument/documentSymbol(2688) 56891 ms
I[11:33:28.562] --> reply:textDocument/documentHighlight(2689) 56896 ms
I[11:33:28.572] --> reply:textDocument/semanticTokens/full(2690) 56907 ms
I[11:33:28.574] --> reply:textDocument/codeAction(2691) 56909 ms, error: Task was cancelled.
I[11:33:28.574] --> reply:textDocument/documentLink(2692) 56907 ms
I[11:33:28.575] --> reply:textDocument/codeAction(2693) 56731 ms
I[11:33:28.578] --> reply:textDocument/inlayHint(2694) 56378 ms
I[11:33:28.578] --> reply:textDocument/hover(2695) 52978 ms, error: Task was cancelled.
I[11:33:28.578] --> reply:textDocument/hover(2696) 52579 ms, error: Task was cancelled.
I[11:33:28.578] --> reply:textDocument/hover(2697) 51494 ms, error: Task was cancelled.
I[11:33:28.578] --> reply:textDocument/definition(2698) 51394 ms
I[11:33:28.578] --> reply:textDocument/hover(2699) 33923 ms, error: Task was cancelled.
The extension arguments are:
"clangd.arguments": [
"--background-index",
"--clang-tidy",
"--completion-style=detailed",
"--header-insertion=never",
"-j=40",
"--pch-storage=memory"
],
additionally, CPU usage show in htop is low and seems like parallel setting has no effect.

Output of clangd --version:
clangd version 15.0.6
Features: linux
Platform: x86_64-unknown-linux-gnu

Editor/LSP plugin:
vscode/clangd extension

Operating system:
centos7 kernel 3.10.0-1160.el7.x86_64

[HighCommander4]

A few questions to try to narrow the issue down:

• Does this happen with all files? Or all files in a particular project? Or a specific file / files in a project?
• How big (lnes of code) is the affected file? How long does it take to recompile the file when rebuilding after making a change to it?
• Do you see one CPU core being used heavily during those 30-60 seconds? (It's expected that the -j setting does not make a difference when opening a single file. It mostly has an effect on background indexing which processes multiple files in parallel.)

[ljpsevenc]

1. It happens with almost all .cpp files and some headers in a particular project.
2. Affected files vary from 500 lines to 3000 lines, in the case of .cpp files, the recompile after making change takes about 2~3secs.
3. Yes.

[HighCommander4]

the recompile after making change takes about 2~3secs

Are you using clang as your compiler, or something else?

A possible diagnostic step that might produce some interesting information would be to attach the debugger to the clangd process, interrupt it a few times during the 30-60s pause, and get stack traces to see what clangd is doing at that time.