server: gosigar ProcFDUsage can be expensive

[stevendanna]

Describe the problem

In a recent large scale test, I was surprised to see a non-trivial amount of CPU time being spent getting our FD usage:

One potential improvement is that the linux implementation in the underlying library is using ioutil.ReadDir which is going to stat every file:

https://github.com/elastic/gosigar/blob/d69e91c3bbdd073073eb0b8e3ba2dde0d969b892/sigar_linux.go#L93C14-L98

It appears that removing these calls would probably be rather helpful.

Using os.ReadDir for this would probably help.

Jira issue: CRDB-51271

[blathers-crl]

Hi @stevendanna, please add branch-* labels to identify which branch(es) this C-bug affects.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[stevendanna]

I've opened a potential improvement here: elastic/gosigar#189

[blathers-crl]

Hi @stevendanna, please add branch-* labels to identify which branch(es) this C-bug affects.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}