[v2,0/5] Speed up git-notes show

Message

Maarten Bosmans Feb. 18, 2024, 7:59 p.m. UTC

First time contributor here, trying my first git.git patch series.

BACKGROUND
  We have a script that runs a range of build tests for all new commits in the
  repository and adds a line to the commit note with the result from the test.
  Something along the lines of:
      occa-build-jit-gnu-cuda-develop: PASSED (<hostname>, 2024-01-01 00:00:00+01:00)
  Pretty useful to quickly check that all commits at least build, not only for
  master, but also in progress feature branches.  (a passing test suite is
  generally only required at the merge point)

PROBLEM
  The bash script loops over all remote refs and lists the commits newer than
  <N> days ago.  For each commit its note is read and grep'ed for an existing
  test name to see whether the build test needs to run again.  The `git note show`
  command that is in this loop nest only takes 14ms to execute, but as it is in
  a loop, those times add up.

ANALYSIS
  When asked to show a note for a specific commit, git looks up the blob hash
  for the note and executes `git show` with that hash.  That of course adds
  the child process overhead, but also causes the initialization of a lot of
  log related configuration, such as for decorations or the mailmap.  Simply
  outputting the blob directly in the main process reduces the run time by
  almost halve.

When looking through the git show implementation for useful stuff that command
does that should also be done when showing a note, I could only find the
`setup_pager()` call and some optional textconv stuff.

The second commit is the main one fixing performance. The others are just
eliminating some overhead I noticed when going through the git notes code.


CHANGES WRT V1
  Sharing of the show_blob_object() function from log.c. The intention here is
  to have `git notes show` behave the same as `git show` when in the future the
  latter might be changed to have more sophisticated behaviour for some blobs,
  e.g. launching an image viewer for PNG blobs.  Non-blob notes are still not
  handled, just like in V1.  Current master does handle that, but that is not
  deemed a case worth handling.


Maarten Bosmans (5):
  log: Move show_blob_object() to log.c
  notes: avoid launching a child process to show a note blob
  notes: use existing function stream_blob_to_fd
  notes: do not clean up right before calling die()
  notes: use strbuf_attach to take ownership of the object contents

 Makefile        |  1 +
 builtin/log.c   | 39 +++++----------------------------------
 builtin/notes.c | 38 +++++++++++---------------------------
 log.c           | 41 +++++++++++++++++++++++++++++++++++++++++
 log.h           | 11 +++++++++++
 5 files changed, 69 insertions(+), 61 deletions(-)
 create mode 100644 log.c
 create mode 100644 log.h