On Fri, Sep 30, 2016 at 05:19:37PM -0700, Junio C Hamano wrote:
> Introduce a mechanism, where we estimate the number of objects in
> the repository upon the first request to abbreviate an object name
> with the default setting and come up with a sane default for the
> repository. Based on the expectation that we would see collision in
> a repository with 2^(2N) objects when using object names shortened
> to first N bits, use sufficient number of hexdigits to cover the
> number of objects in the repository. Each hexdigit (4-bits) we add
> to the shortened name allows us to have four times (2-bits) as many
> objects in the repository.
>
> ---
> cache.h | 1 +
> environment.c | 2 +-
> sha1_name.c | 28 +++++++++++++++++++++++++++-
> 3 files changed, 29 insertions(+), 2 deletions(-)
For reference, here's a working version that just uses a separate
counting function (no commit message, because I would just steal the one
from Linus ;) ).
---
cache.h | 6 ++++++
environment.c | 2 +-
sha1_file.c | 27 +++++++++++++++++++++++++++
sha1_name.c | 20 ++++++++++++++++++++
4 files changed, 54 insertions(+), 1 deletion(-)
diff --git a/cache.h b/cache.h
index 5a651b8..f22ace5 100644
--- a/cache.h
+++ b/cache.h
@@ -1455,6 +1455,12 @@ extern void prepare_packed_git(void);
extern void reprepare_packed_git(void);
extern void install_packed_git(struct packed_git *pack);
+/*
+ * Give a rough count of objects in the repository. This sacrifices accuracy
+ * for speed.
+ */
+unsigned long approximate_object_count(void);
+
extern struct packed_git *find_sha1_pack(const unsigned char *sha1,
struct packed_git *packs);
diff --git a/environment.c b/environment.c
index 44fb107..6f9d290 100644
--- a/environment.c
+++ b/environment.c
@@ -16,7 +16,7 @@ int trust_executable_bit = 1;
int trust_ctime = 1;
int check_stat = 1;
int has_symlinks = 1;
-int minimum_abbrev = 4, default_abbrev = FALLBACK_DEFAULT_ABBREV;
+int minimum_abbrev = 4, default_abbrev = -1;
int ignore_case;
int assume_unchanged;
int prefer_symlink_refs;
diff --git a/sha1_file.c b/sha1_file.c
index b9c1fa3..4882440 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1381,6 +1381,32 @@ static void prepare_packed_git_one(char *objdir, int local)
strbuf_release(&path);
}
+static int approximate_object_count_valid;
+
+/*
+ * Give a fast, rough count of the number of objects in the repository. This
+ * ignores loose objects completely. If you have a lot of them, then either
+ * you should repack because your performance will be awful, or they are
+ * all unreachable objects about to be pruned, in which case they're not really
+ * interesting as a measure of repo size in the first place.
+ */
+unsigned long approximate_object_count(void)
+{
+ static unsigned long count;
+ if (!approximate_object_count_valid) {
+ struct packed_git *p;
+
+ prepare_packed_git();
+ count = 0;
+ for (p = packed_git; p; p = p->next) {
+ if (open_pack_index(p))
+ continue;
+ count += p->num_objects;
+ }
+ }
+ return count;
+}
+
static void *get_next_packed_git(const void *p)
{
return ((const struct packed_git *)p)->next;
@@ -1455,6 +1481,7 @@ void prepare_packed_git(void)
void reprepare_packed_git(void)
{
+ approximate_object_count_valid = 0;
prepare_packed_git_run_once = 0;
prepare_packed_git();
}
diff --git a/sha1_name.c b/sha1_name.c
index 3b647fd..ecc4b54 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -455,10 +455,30 @@ int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
return ret;
}
+/*
+ * Return the slot of the most-significant bit set in "val". There are various
+ * ways to do this quickly with fls() or __builtin_clzl(), but speed is
+ * probably not a big deal here.
+ */
+unsigned msb(unsigned long val)
+{
+ unsigned r = 0;
+ while (val >>= 1)
+ r++;
+ return r;
+}
+
int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
{
int status, exists;
+ if (len < 0) {
+ unsigned long count = approximate_object_count();
+ len = (msb(count) + 1) / 2;
+ if (len < 0)
+ len = FALLBACK_DEFAULT_ABBREV;
+ }
+
sha1_to_hex_r(hex, sha1);
if (len == 40 || !len)
return 40;
--
2.10.0.618.g82cc264