[PATCH 0/1] send-pack: set core.warnAmbiguousRefs=false

I've been looking into the performance of git push for very large repos. Our users are reporting that 60-80% of git push time is spent during the "Enumerating objects" phase of git pack-objects.

A git push process runs several processes during its run, but one includes git send-pack which calls git pack-objects and passes the known have/wants into stdin using object ids. However, the default setting for core.warnAmbiguousRefs requires git pack-objects to check for ref names matching the ref_rev_parse_rules array in refs.c. This means that every object is triggering at least six "file exists?" queries.

When there are a lot of refs, this can add up significantly! My PerfView trace for a simple push measured 3 seconds spent checking these paths.

The fix for this is simple: set core.warnAmbiguousRefs to false for this specific call of git pack-objects coming from git send-pack. We don't want to default it to false for all calls to git pack-objects, as it is valid to pass ref names instead of object ids. This helps regain these seconds during a push.

In addition to this patch submission, we are looking into merging it into our fork sooner [1].

[1] https://github.com/Microsoft/git/pull/67

Derrick Stolee (1):
  send-pack: set core.warnAmbiguousRefs=false

 send-pack.c | 2 ++
 1 file changed, 2 insertions(+)

base-commit: cae598d9980661a978e2df4fb338518f7bf09572
Published-As: https://github.com/gitgitgadget/git/releases/tags/pr-68%2Fderrickstolee%2Fsend-pack-config-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-68/derrickstolee/send-pack-config-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/68