pack-objects: use bitmaps when packing objects
In this patch, we use the bitmap API to perform the `Counting Objects`
phase in pack-objects, rather than a traditional walk through the object
graph. For a reasonably-packed large repo, the time to fetch and clone
is often dominated by the full-object revision walk during the Counting
Objects phase. Using bitmaps can reduce the CPU time required on the
server (and therefore start sending the actual pack data with less
delay).
For bitmaps to be used, the following must be true:
1. We must be packing to stdout (as a normal `pack-objects` from
`upload-pack` would do).
2. There must be a .bitmap index containing at least one of the
"have" objects that the client is asking for.
3. Bitmaps must be enabled (they are enabled by default, but can be
disabled by setting `pack.usebitmaps` to false, or by using
`--no-use-bitmap-index` on the command-line).
If any of these is not true, we fall back to doing a normal walk of the
object graph.
Here are some sample timings from a full pack of `torvalds/linux` (i.e.
something very similar to what would be generated for a clone of the
repository) that show the speedup produced by various
methods:
[existing graph traversal]
$ time git pack-objects --all --stdout --no-use-bitmap-index \
</dev/null >/dev/null
Counting objects: 3237103, done.
Compressing objects: 100% (508752/508752), done.
Total 3237103 (delta 2699584), reused 3237103 (delta 2699584)
real 0m44.111s
user 0m42.396s
sys 0m3.544s
[bitmaps only, without partial pack reuse; note that
pack reuse is automatic, so timing this required a
patch to disable it]
$ time git pack-objects --all --stdout </dev/null >/dev/null
Counting objects: 3237103, done.
Compressing objects: 100% (508752/508752), done.
Total 3237103 (delta 2699584), reused 3237103 (delta 2699584)
real 0m5.413s
user 0m5.604s
sys 0m1.804s
[bitmaps with pack reuse (what you get with this patch)]
$ time git pack-objects --all --stdout </dev/null >/dev/null
Reusing existing pack: 3237103, done.
Total 3237103 (delta 0), reused 0 (delta 0)
real 0m1.636s
user 0m1.460s
sys 0m0.172s
Signed-off-by: Vicent Marti <tanoku@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 13b171d..030d894 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -19,6 +19,7 @@
#include "refs.h"
#include "streaming.h"
#include "thread-utils.h"
+#include "pack-bitmap.h"
static const char *pack_usage[] = {
N_("git pack-objects --stdout [options...] [< ref-list | < object-list]"),
@@ -57,6 +58,12 @@
static int pack_compression_level = Z_DEFAULT_COMPRESSION;
static int pack_compression_seen;
+static struct packed_git *reuse_packfile;
+static uint32_t reuse_packfile_objects;
+static off_t reuse_packfile_offset;
+
+static int use_bitmap_index = 1;
+
static unsigned long delta_cache_size = 0;
static unsigned long max_delta_cache_size = 256 * 1024 * 1024;
static unsigned long cache_max_small_delta_size = 1000;
@@ -678,6 +685,46 @@
return wo;
}
+static off_t write_reused_pack(struct sha1file *f)
+{
+ unsigned char buffer[8192];
+ off_t to_write;
+ int fd;
+
+ if (!is_pack_valid(reuse_packfile))
+ die("packfile is invalid: %s", reuse_packfile->pack_name);
+
+ fd = git_open_noatime(reuse_packfile->pack_name);
+ if (fd < 0)
+ die_errno("unable to open packfile for reuse: %s",
+ reuse_packfile->pack_name);
+
+ if (lseek(fd, sizeof(struct pack_header), SEEK_SET) == -1)
+ die_errno("unable to seek in reused packfile");
+
+ if (reuse_packfile_offset < 0)
+ reuse_packfile_offset = reuse_packfile->pack_size - 20;
+
+ to_write = reuse_packfile_offset - sizeof(struct pack_header);
+
+ while (to_write) {
+ int read_pack = xread(fd, buffer, sizeof(buffer));
+
+ if (read_pack <= 0)
+ die_errno("unable to read from reused packfile");
+
+ if (read_pack > to_write)
+ read_pack = to_write;
+
+ sha1write(f, buffer, read_pack);
+ to_write -= read_pack;
+ }
+
+ close(fd);
+ written += reuse_packfile_objects;
+ return reuse_packfile_offset - sizeof(struct pack_header);
+}
+
static void write_pack_file(void)
{
uint32_t i = 0, j;
@@ -704,6 +751,15 @@
offset = write_pack_header(f, nr_remaining);
if (!offset)
die_errno("unable to write pack header");
+
+ if (reuse_packfile) {
+ off_t packfile_size;
+ assert(pack_to_stdout);
+
+ packfile_size = write_reused_pack(f);
+ offset += packfile_size;
+ }
+
nr_written = 0;
for (; i < to_pack.nr_objects; i++) {
struct object_entry *e = write_order[i];
@@ -923,6 +979,22 @@
return 1;
}
+static int add_object_entry_from_bitmap(const unsigned char *sha1,
+ enum object_type type,
+ int flags, uint32_t name_hash,
+ struct packed_git *pack, off_t offset)
+{
+ uint32_t index_pos;
+
+ if (have_duplicate_entry(sha1, 0, &index_pos))
+ return 0;
+
+ create_object_entry(sha1, type, name_hash, 0, 0, index_pos, pack, offset);
+
+ display_progress(progress_state, to_pack.nr_objects);
+ return 1;
+}
+
struct pbase_tree_cache {
unsigned char sha1[20];
int ref;
@@ -2085,6 +2157,10 @@
cache_max_small_delta_size = git_config_int(k, v);
return 0;
}
+ if (!strcmp(k, "pack.usebitmaps")) {
+ use_bitmap_index = git_config_bool(k, v);
+ return 0;
+ }
if (!strcmp(k, "pack.threads")) {
delta_search_threads = git_config_int(k, v);
if (delta_search_threads < 0)
@@ -2293,6 +2369,29 @@
}
}
+static int get_object_list_from_bitmap(struct rev_info *revs)
+{
+ if (prepare_bitmap_walk(revs) < 0)
+ return -1;
+
+ if (!reuse_partial_packfile_from_bitmap(
+ &reuse_packfile,
+ &reuse_packfile_objects,
+ &reuse_packfile_offset)) {
+ assert(reuse_packfile_objects);
+ nr_result += reuse_packfile_objects;
+
+ if (progress) {
+ fprintf(stderr, "Reusing existing pack: %d, done.\n",
+ reuse_packfile_objects);
+ fflush(stderr);
+ }
+ }
+
+ traverse_bitmap_commit_list(&add_object_entry_from_bitmap);
+ return 0;
+}
+
static void get_object_list(int ac, const char **av)
{
struct rev_info revs;
@@ -2320,6 +2419,9 @@
die("bad revision '%s'", line);
}
+ if (use_bitmap_index && !get_object_list_from_bitmap(&revs))
+ return;
+
if (prepare_revision_walk(&revs))
die("revision walk setup failed");
mark_edges_uninteresting(&revs, show_edge);
@@ -2449,6 +2551,8 @@
N_("pack compression level")),
OPT_SET_INT(0, "keep-true-parents", &grafts_replace_parents,
N_("do not hide commits by grafts"), 0),
+ OPT_BOOL(0, "use-bitmap-index", &use_bitmap_index,
+ N_("use a bitmap index if available to speed up counting objects")),
OPT_END(),
};
@@ -2515,6 +2619,9 @@
if (keep_unreachable && unpack_unreachable)
die("--keep-unreachable and --unpack-unreachable are incompatible.");
+ if (!use_internal_rev_list || !pack_to_stdout || is_repository_shallow())
+ use_bitmap_index = 0;
+
if (progress && all_progress_implied)
progress = 2;
