[Bug 230491] stat(1): Improve performance with getpwuid() and getgrgid() caching

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=230491

--- Comment #12 from commit-hook at freebsd.org ---
A commit references this bug:

Author: cem
Date: Sat Aug 11 02:56:44 UTC 2018
New revision: 337600
URL: https://svnweb.freebsd.org/changeset/base/337600

Log:
  stat(1): cache id->name resolution

  When invoked on a large list of files, it is most common for a small number
of
  uids/gids to own most of the results.

  Like ls(1), use pwcache(3) to avoid repeatedly looking up the same IDs.

  Example microbenchmark and non-scientific results:

  $ time (find /usr/src -type f -print0 | xargs -0 stat >/dev/null)

  BEFORE:
  3.62s user 5.23s system 102% cpu 8.655 total
  3.47s user 5.38s system 102% cpu 8.647 total

  AFTER:
  1.23s user 1.81s system 108% cpu 2.810 total
  1.43s user 1.54s system 107% cpu 2.754 total

  Does this microbenchmark have any real-world significance?  Until a use case
  is demonstrated otherwise, I doubt it.  Ordinarily I would be resistant to
  optimizing pointless microbenchmarks in base utilities (e.g., recent totally
  gratuitous changes to yes(1)).  However, the pwcache(3) APIs actually
  simplify stat(1) logic ever so slightly compared to the raw APIs they wrap,
  so I think this is at worst harmless.

  PR:           230491
  Reported by:  Thomas Hurst <tom AT hur.st>
  Discussed with:       gad@

Changes:
  head/usr.bin/stat/stat.c

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