Performance regression in `git branch` due to ref-filter usage
- Date: Wed, 17 May 2017 13:14:34 +0200
- From: Michael Haggerty <mhagger@xxxxxxxxxxxx>
- Subject: Performance regression in `git branch` due to ref-filter usage
While working on reference code, I was running `git branch` under
`strace`, when I noticed that `$GIT_DIR/HEAD` was being `lstat()`ed and
`read()` 121 times. This is in a repository with 114 branches, so
probably it is being run once per branch. The extra work makes a
measurable difference to the (admittedly, short) runtime.
As recently as 2.12.3 the file was only read 4 times when running the
same command .
The regression bisects to
949af0684c (branch: use ref-filter printing APIs, 2017-01-10)
It would be nice if these extra syscalls could be avoided.
I haven't checked whether other commands have similar regressions.
 One wonders why the file has to be read more than once, but that's a
different story and probably harder to fix.