[PATCH 2/4] limit "contains" traversals based on commit timestamp
- From
Ævar Arnfjörð Bjarmason <avarab@gmail.com>
- Date
- Jun 11, 2011, 19:04 UTC
- Message-ID
- <1307819051-25748-3-git-send-email-avarab@gmail.com>
- In-Reply-To
- <1307819051-25748-1-git-send-email-avarab@gmail.com>
From: Jeff King <peff@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~200" in the linux-2.6 repository goes from:
real 0m5.302s user 0m5.116s sys 0m0.184s
to:
real 0m0.030s user 0m0.020s sys 0m0.008s
The downside is that we will no longer find some answers in the face of extreme clock skew, as we will stop the traversal early when seeing commits skewed too far into the past.
Name-rev already implements a similar optimization, using a "slop" of one day to allow for a certain amount of clock skew in commit timestamps. This patch introduces a "core.clockskew" variable, which allows specifying the allowable amount of clock skew in seconds. For safety, it defaults to "none", causing a full traversal (i.e., no change in behavior from previous versions).
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> --- builtin/tag.c | 36 +++++++++++++++++++++++++++++++++--- 1 files changed, 33 insertions(+), 3 deletions(-)
diff --git a/builtin/tag.c b/builtin/tag.c index 575a03c..0f0d784 100644 --- a/builtin/tag.c +++ b/builtin/tag.c @@ -25,6 +25,8 @@ static const char * const git_tag_usage[] = { static char signingkey[1000]; +static int core_clock_skew = -1; + struct tag_filter { const char *pattern; int lines; @@ -40,7 +42,8 @@ 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 +60,13 @@ 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 (candidate->date < 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 +77,22 @@ static int contains_recurse(struct commit *candidate, int contains(struct commit *candidate, const struct commit_list *want) { - return contains_recurse(candidate, want); + unsigned long cutoff = 0; + + if (core_clock_skew >= 0) { + const struct commit_list *c; + unsigned long min_date = ULONG_MAX; + for (c = want; c; c = c->next) { + if (parse_commit(c->item) < 0) + continue; + if (c->item->date < min_date) + min_date = c->item->date; + } + if (min_date > core_clock_skew) + cutoff = min_date - core_clock_skew; + } + + return contains_recurse(candidate, want, cutoff); } static int show_reference(const char *refname, const unsigned char *sha1, @@ -277,6 +299,14 @@ static int git_tag_config(const char *var, const char *value, void *cb) return 0; } + if (!strcmp(var, "core.clockskew")) { + if (!value || !strcmp(value, "none")) + core_clock_skew = -1; + else + core_clock_skew = git_config_int(var, value); + return 0; + } + return git_default_config(var, value, cb); }
-- 1.7.5.3