git/pack-bitmap-write.c
Vicent Marti ae4f07fbcc pack-bitmap: implement optional name_hash cache
When we use pack bitmaps rather than walking the object
graph, we end up with the list of objects to include in the
packfile, but we do not know the path at which any tree or
blob objects would be found.

In a recently packed repository, this is fine. A fetch would
use the paths only as a heuristic in the delta compression
phase, and a fully packed repository should not need to do
much delta compression.

As time passes, though, we may acquire more objects on top
of our large bitmapped pack. If clients fetch frequently,
then they never even look at the bitmapped history, and all
works as usual. However, a client who has not fetched since
the last bitmap repack will have "have" tips in the
bitmapped history, but "want" newer objects.

The bitmaps themselves degrade gracefully in this
circumstance. We manually walk the more recent bits of
history, and then use bitmaps when we hit them.

But we would also like to perform delta compression between
the newer objects and the bitmapped objects (both to delta
against what we know the user already has, but also between
"new" and "old" objects that the user is fetching). The lack
of pathnames makes our delta heuristics much less effective.

This patch adds an optional cache of the 32-bit name_hash
values to the end of the bitmap file. If present, a reader
can use it to match bitmapped and non-bitmapped names during
delta compression.

Here are perf results for p5310:

Test                      origin/master       HEAD^                      HEAD
-------------------------------------------------------------------------------------------------
5310.2: repack to disk    36.81(37.82+1.43)   47.70(48.74+1.41) +29.6%   47.75(48.70+1.51) +29.7%
5310.3: simulated clone   30.78(29.70+2.14)   1.08(0.97+0.10) -96.5%     1.07(0.94+0.12) -96.5%
5310.4: simulated fetch   3.16(6.10+0.08)     3.54(10.65+0.06) +12.0%    1.70(3.07+0.06) -46.2%
5310.6: partial bitmap    36.76(43.19+1.81)   6.71(11.25+0.76) -81.7%    4.08(6.26+0.46) -88.9%

You can see that the time spent on an incremental fetch goes
down, as our delta heuristics are able to do their work.
And we save time on the partial bitmap clone for the same
reason.

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>
2013-12-30 12:19:23 -08:00

553 lines
12 KiB
C

#include "cache.h"
#include "commit.h"
#include "tag.h"
#include "diff.h"
#include "revision.h"
#include "list-objects.h"
#include "progress.h"
#include "pack-revindex.h"
#include "pack.h"
#include "pack-bitmap.h"
#include "sha1-lookup.h"
#include "pack-objects.h"
struct bitmapped_commit {
struct commit *commit;
struct ewah_bitmap *bitmap;
struct ewah_bitmap *write_as;
int flags;
int xor_offset;
uint32_t commit_pos;
};
struct bitmap_writer {
struct ewah_bitmap *commits;
struct ewah_bitmap *trees;
struct ewah_bitmap *blobs;
struct ewah_bitmap *tags;
khash_sha1 *bitmaps;
khash_sha1 *reused;
struct packing_data *to_pack;
struct bitmapped_commit *selected;
unsigned int selected_nr, selected_alloc;
struct progress *progress;
int show_progress;
unsigned char pack_checksum[20];
};
static struct bitmap_writer writer;
void bitmap_writer_show_progress(int show)
{
writer.show_progress = show;
}
/**
* Build the initial type index for the packfile
*/
void bitmap_writer_build_type_index(struct pack_idx_entry **index,
uint32_t index_nr)
{
uint32_t i;
writer.commits = ewah_new();
writer.trees = ewah_new();
writer.blobs = ewah_new();
writer.tags = ewah_new();
for (i = 0; i < index_nr; ++i) {
struct object_entry *entry = (struct object_entry *)index[i];
enum object_type real_type;
entry->in_pack_pos = i;
switch (entry->type) {
case OBJ_COMMIT:
case OBJ_TREE:
case OBJ_BLOB:
case OBJ_TAG:
real_type = entry->type;
break;
default:
real_type = sha1_object_info(entry->idx.sha1, NULL);
break;
}
switch (real_type) {
case OBJ_COMMIT:
ewah_set(writer.commits, i);
break;
case OBJ_TREE:
ewah_set(writer.trees, i);
break;
case OBJ_BLOB:
ewah_set(writer.blobs, i);
break;
case OBJ_TAG:
ewah_set(writer.tags, i);
break;
default:
die("Missing type information for %s (%d/%d)",
sha1_to_hex(entry->idx.sha1), real_type, entry->type);
}
}
}
/**
* Compute the actual bitmaps
*/
static struct object **seen_objects;
static unsigned int seen_objects_nr, seen_objects_alloc;
static inline void push_bitmapped_commit(struct commit *commit, struct ewah_bitmap *reused)
{
if (writer.selected_nr >= writer.selected_alloc) {
writer.selected_alloc = (writer.selected_alloc + 32) * 2;
writer.selected = xrealloc(writer.selected,
writer.selected_alloc * sizeof(struct bitmapped_commit));
}
writer.selected[writer.selected_nr].commit = commit;
writer.selected[writer.selected_nr].bitmap = reused;
writer.selected[writer.selected_nr].flags = 0;
writer.selected_nr++;
}
static inline void mark_as_seen(struct object *object)
{
ALLOC_GROW(seen_objects, seen_objects_nr + 1, seen_objects_alloc);
seen_objects[seen_objects_nr++] = object;
}
static inline void reset_all_seen(void)
{
unsigned int i;
for (i = 0; i < seen_objects_nr; ++i) {
seen_objects[i]->flags &= ~(SEEN | ADDED | SHOWN);
}
seen_objects_nr = 0;
}
static uint32_t find_object_pos(const unsigned char *sha1)
{
struct object_entry *entry = packlist_find(writer.to_pack, sha1, NULL);
if (!entry) {
die("Failed to write bitmap index. Packfile doesn't have full closure "
"(object %s is missing)", sha1_to_hex(sha1));
}
return entry->in_pack_pos;
}
static void show_object(struct object *object, const struct name_path *path,
const char *last, void *data)
{
struct bitmap *base = data;
bitmap_set(base, find_object_pos(object->sha1));
mark_as_seen(object);
}
static void show_commit(struct commit *commit, void *data)
{
mark_as_seen((struct object *)commit);
}
static int
add_to_include_set(struct bitmap *base, struct commit *commit)
{
khiter_t hash_pos;
uint32_t bitmap_pos = find_object_pos(commit->object.sha1);
if (bitmap_get(base, bitmap_pos))
return 0;
hash_pos = kh_get_sha1(writer.bitmaps, commit->object.sha1);
if (hash_pos < kh_end(writer.bitmaps)) {
struct bitmapped_commit *bc = kh_value(writer.bitmaps, hash_pos);
bitmap_or_ewah(base, bc->bitmap);
return 0;
}
bitmap_set(base, bitmap_pos);
return 1;
}
static int
should_include(struct commit *commit, void *_data)
{
struct bitmap *base = _data;
if (!add_to_include_set(base, commit)) {
struct commit_list *parent = commit->parents;
mark_as_seen((struct object *)commit);
while (parent) {
parent->item->object.flags |= SEEN;
mark_as_seen((struct object *)parent->item);
parent = parent->next;
}
return 0;
}
return 1;
}
static void compute_xor_offsets(void)
{
static const int MAX_XOR_OFFSET_SEARCH = 10;
int i, next = 0;
while (next < writer.selected_nr) {
struct bitmapped_commit *stored = &writer.selected[next];
int best_offset = 0;
struct ewah_bitmap *best_bitmap = stored->bitmap;
struct ewah_bitmap *test_xor;
for (i = 1; i <= MAX_XOR_OFFSET_SEARCH; ++i) {
int curr = next - i;
if (curr < 0)
break;
test_xor = ewah_pool_new();
ewah_xor(writer.selected[curr].bitmap, stored->bitmap, test_xor);
if (test_xor->buffer_size < best_bitmap->buffer_size) {
if (best_bitmap != stored->bitmap)
ewah_pool_free(best_bitmap);
best_bitmap = test_xor;
best_offset = i;
} else {
ewah_pool_free(test_xor);
}
}
stored->xor_offset = best_offset;
stored->write_as = best_bitmap;
next++;
}
}
void bitmap_writer_build(struct packing_data *to_pack)
{
static const double REUSE_BITMAP_THRESHOLD = 0.2;
int i, reuse_after, need_reset;
struct bitmap *base = bitmap_new();
struct rev_info revs;
writer.bitmaps = kh_init_sha1();
writer.to_pack = to_pack;
if (writer.show_progress)
writer.progress = start_progress("Building bitmaps", writer.selected_nr);
init_revisions(&revs, NULL);
revs.tag_objects = 1;
revs.tree_objects = 1;
revs.blob_objects = 1;
revs.no_walk = 0;
revs.include_check = should_include;
reset_revision_walk();
reuse_after = writer.selected_nr * REUSE_BITMAP_THRESHOLD;
need_reset = 0;
for (i = writer.selected_nr - 1; i >= 0; --i) {
struct bitmapped_commit *stored;
struct object *object;
khiter_t hash_pos;
int hash_ret;
stored = &writer.selected[i];
object = (struct object *)stored->commit;
if (stored->bitmap == NULL) {
if (i < writer.selected_nr - 1 &&
(need_reset ||
!in_merge_bases(writer.selected[i + 1].commit,
stored->commit))) {
bitmap_reset(base);
reset_all_seen();
}
add_pending_object(&revs, object, "");
revs.include_check_data = base;
if (prepare_revision_walk(&revs))
die("revision walk setup failed");
traverse_commit_list(&revs, show_commit, show_object, base);
revs.pending.nr = 0;
revs.pending.alloc = 0;
revs.pending.objects = NULL;
stored->bitmap = bitmap_to_ewah(base);
need_reset = 0;
} else
need_reset = 1;
if (i >= reuse_after)
stored->flags |= BITMAP_FLAG_REUSE;
hash_pos = kh_put_sha1(writer.bitmaps, object->sha1, &hash_ret);
if (hash_ret == 0)
die("Duplicate entry when writing index: %s",
sha1_to_hex(object->sha1));
kh_value(writer.bitmaps, hash_pos) = stored;
display_progress(writer.progress, writer.selected_nr - i);
}
bitmap_free(base);
stop_progress(&writer.progress);
compute_xor_offsets();
}
/**
* Select the commits that will be bitmapped
*/
static inline unsigned int next_commit_index(unsigned int idx)
{
static const unsigned int MIN_COMMITS = 100;
static const unsigned int MAX_COMMITS = 5000;
static const unsigned int MUST_REGION = 100;
static const unsigned int MIN_REGION = 20000;
unsigned int offset, next;
if (idx <= MUST_REGION)
return 0;
if (idx <= MIN_REGION) {
offset = idx - MUST_REGION;
return (offset < MIN_COMMITS) ? offset : MIN_COMMITS;
}
offset = idx - MIN_REGION;
next = (offset < MAX_COMMITS) ? offset : MAX_COMMITS;
return (next > MIN_COMMITS) ? next : MIN_COMMITS;
}
static int date_compare(const void *_a, const void *_b)
{
struct commit *a = *(struct commit **)_a;
struct commit *b = *(struct commit **)_b;
return (long)b->date - (long)a->date;
}
void bitmap_writer_reuse_bitmaps(struct packing_data *to_pack)
{
if (prepare_bitmap_git() < 0)
return;
writer.reused = kh_init_sha1();
rebuild_existing_bitmaps(to_pack, writer.reused, writer.show_progress);
}
static struct ewah_bitmap *find_reused_bitmap(const unsigned char *sha1)
{
khiter_t hash_pos;
if (!writer.reused)
return NULL;
hash_pos = kh_get_sha1(writer.reused, sha1);
if (hash_pos >= kh_end(writer.reused))
return NULL;
return kh_value(writer.reused, hash_pos);
}
void bitmap_writer_select_commits(struct commit **indexed_commits,
unsigned int indexed_commits_nr,
int max_bitmaps)
{
unsigned int i = 0, j, next;
qsort(indexed_commits, indexed_commits_nr, sizeof(indexed_commits[0]),
date_compare);
if (writer.show_progress)
writer.progress = start_progress("Selecting bitmap commits", 0);
if (indexed_commits_nr < 100) {
for (i = 0; i < indexed_commits_nr; ++i)
push_bitmapped_commit(indexed_commits[i], NULL);
return;
}
for (;;) {
struct ewah_bitmap *reused_bitmap = NULL;
struct commit *chosen = NULL;
next = next_commit_index(i);
if (i + next >= indexed_commits_nr)
break;
if (max_bitmaps > 0 && writer.selected_nr >= max_bitmaps) {
writer.selected_nr = max_bitmaps;
break;
}
if (next == 0) {
chosen = indexed_commits[i];
reused_bitmap = find_reused_bitmap(chosen->object.sha1);
} else {
chosen = indexed_commits[i + next];
for (j = 0; j <= next; ++j) {
struct commit *cm = indexed_commits[i + j];
reused_bitmap = find_reused_bitmap(cm->object.sha1);
if (reused_bitmap || (cm->object.flags & NEEDS_BITMAP) != 0) {
chosen = cm;
break;
}
if (cm->parents && cm->parents->next)
chosen = cm;
}
}
push_bitmapped_commit(chosen, reused_bitmap);
i += next + 1;
display_progress(writer.progress, i);
}
stop_progress(&writer.progress);
}
static int sha1write_ewah_helper(void *f, const void *buf, size_t len)
{
/* sha1write will die on error */
sha1write(f, buf, len);
return len;
}
/**
* Write the bitmap index to disk
*/
static inline void dump_bitmap(struct sha1file *f, struct ewah_bitmap *bitmap)
{
if (ewah_serialize_to(bitmap, sha1write_ewah_helper, f) < 0)
die("Failed to write bitmap index");
}
static const unsigned char *sha1_access(size_t pos, void *table)
{
struct pack_idx_entry **index = table;
return index[pos]->sha1;
}
static void write_selected_commits_v1(struct sha1file *f,
struct pack_idx_entry **index,
uint32_t index_nr)
{
int i;
for (i = 0; i < writer.selected_nr; ++i) {
struct bitmapped_commit *stored = &writer.selected[i];
struct bitmap_disk_entry on_disk;
int commit_pos =
sha1_pos(stored->commit->object.sha1, index, index_nr, sha1_access);
if (commit_pos < 0)
die("BUG: trying to write commit not in index");
on_disk.object_pos = htonl(commit_pos);
on_disk.xor_offset = stored->xor_offset;
on_disk.flags = stored->flags;
sha1write(f, &on_disk, sizeof(on_disk));
dump_bitmap(f, stored->write_as);
}
}
static void write_hash_cache(struct sha1file *f,
struct pack_idx_entry **index,
uint32_t index_nr)
{
uint32_t i;
for (i = 0; i < index_nr; ++i) {
struct object_entry *entry = (struct object_entry *)index[i];
uint32_t hash_value = htonl(entry->hash);
sha1write(f, &hash_value, sizeof(hash_value));
}
}
void bitmap_writer_set_checksum(unsigned char *sha1)
{
hashcpy(writer.pack_checksum, sha1);
}
void bitmap_writer_finish(struct pack_idx_entry **index,
uint32_t index_nr,
const char *filename,
uint16_t options)
{
static char tmp_file[PATH_MAX];
static uint16_t default_version = 1;
static uint16_t flags = BITMAP_OPT_FULL_DAG;
struct sha1file *f;
struct bitmap_disk_header header;
int fd = odb_mkstemp(tmp_file, sizeof(tmp_file), "pack/tmp_bitmap_XXXXXX");
if (fd < 0)
die_errno("unable to create '%s'", tmp_file);
f = sha1fd(fd, tmp_file);
memcpy(header.magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE));
header.version = htons(default_version);
header.options = htons(flags | options);
header.entry_count = htonl(writer.selected_nr);
memcpy(header.checksum, writer.pack_checksum, 20);
sha1write(f, &header, sizeof(header));
dump_bitmap(f, writer.commits);
dump_bitmap(f, writer.trees);
dump_bitmap(f, writer.blobs);
dump_bitmap(f, writer.tags);
write_selected_commits_v1(f, index, index_nr);
if (options & BITMAP_OPT_HASH_CACHE)
write_hash_cache(f, index, index_nr);
sha1close(f, NULL, CSUM_FSYNC);
if (adjust_shared_perm(tmp_file))
die_errno("unable to make temporary bitmap file readable");
if (rename(tmp_file, filename))
die_errno("unable to rename temporary bitmap file to '%s'", filename);
}