Tarfile is unnecessarily slow

[jforberg]

Bug report

Bug description:

There is room for improvement in tarfile write performance. In a simple benchmark I find that tarfile spends most of its time doing repeated user name/group name queries.
https://gist.github.com/jforberg/86af759c796199740c31547ae828aef2

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-121267: Improve performance of tarfile (#121267) #121269

[gaogaotiantian]

Could you paste your cProfile output? I was a bit surprised that most of the time is spent on reading the pwd and grp.

[jforberg]

@gaogaotiantian Here is the output:

cprofile.txt

[picnixz]

Recategorizing this issue as per #121269 (comment).