[RFC/PATCHv2 6/6] limit "contains" traversals based on commit generation
- From
Jeff King <peff@peff.net>
- Date
- Jul 13, 2011, 07:06 UTC
- Message-ID
- <20110713070644.GF18566@sigill.intra.peff.net>
- In-Reply-To
- <20110713064709.GA18499@sigill.intra.peff.net>
When looking for commits that contain other commits (e.g., via "git tag --contains"), we can end up traversing useless portions of the graph. For example, if I am looking for a tag that contains a commit made last week, there is not much point in traversing portions of the history graph made five years ago.
This optimization can provide massive speedups. For example, doing "git tag --contains HEAD~1000" in the linux-2.6 repository goes from:
real 0m3.139s user 0m3.044s sys 0m0.092s
to:
real 0m0.035s user 0m0.028s sys 0m0.004s
We could use commit timestamps to know when we are going too far back in history, but they are sometimes not trustworthy. Extreme clock skew on committers' machines (or bugs in commit-generating software) mean that we may stop the traversal too early when seeing commits skewed into the past.
Instead, we use the calculated commit generation, which is a propery of the graph itself (but since we cache it, it's still cheap to consult).
Signed-off-by: Jeff King <peff@peff.net> --- Same as previous version.
builtin/tag.c | 20 +++++++++++++++++--- 1 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/builtin/tag.c b/builtin/tag.c index 63bce6e..df6de47 100644 --- a/builtin/tag.c +++ b/builtin/tag.c @@ -40,7 +40,8 @@ static int in_commit_list(const struct commit_list *want, struct commit *c) } static int contains_recurse(struct commit *candidate, - const struct commit_list *want) + const struct commit_list *want, + unsigned long cutoff) { struct commit_list *p; @@ -57,9 +58,13 @@ static int contains_recurse(struct commit *candidate, if (parse_commit(candidate) < 0) return 0; + /* stop searching if we go too far back in time */ + if (commit_generation(candidate) < cutoff) + return 0; + /* Otherwise recurse and mark ourselves for future traversals. */ for (p = candidate->parents; p; p = p->next) { - if (contains_recurse(p->item, want)) { + if (contains_recurse(p->item, want, cutoff)) { candidate->object.flags |= TMP_MARK; return 1; } @@ -70,7 +75,16 @@ static int contains_recurse(struct commit *candidate, static int contains(struct commit *candidate, const struct commit_list *want) { - return contains_recurse(candidate, want); + unsigned long cutoff = ULONG_MAX; + const struct commit_list *c; + + for (c = want; c; c = c->next) { + unsigned long g = commit_generation(c->item); + if (g < cutoff) + cutoff = g; + } + + return contains_recurse(candidate, want, cutoff); } static int show_reference(const char *refname, const unsigned char *sha1,
-- 1.7.6.37.g989c6