Jeff King <peff@xxxxxxxx> writes:
> +int commit_metapack(unsigned char *sha1,
> + uint32_t *timestamp,
> + unsigned char **tree,
> + unsigned char **parent1,
> + unsigned char **parent2)
> +{
> + struct commit_metapack *p;
> +
> + prepare_commit_metapacks();
> + for (p = commit_metapacks; p; p = p->next) {
> + unsigned char *data;
> + int pos = sha1_entry_pos(p->index, 20, 0, 0, p->nr, p->nr, sha1);
This is a tangent, but isn't it about time to rip out the check for
GIT_USE_LOOKUP in find_pack_entry_one(), I wonder.
> + prepare_commit_metapacks();
> + for (p = commit_metapacks; p; p = p->next) {
> + unsigned char *data;
> + int pos = sha1_entry_pos(p->index, 20, 0, 0, p->nr, p->nr, sha1);
> + if (pos < 0)
> + continue;
> +
> + /* timestamp(4) + tree(20) + parents(40) */
> + data = p->data + 64 * pos;
> + *timestamp = *(uint32_t *)data;
> + *timestamp = ntohl(*timestamp);
> + data += 4;
> + *tree = data;
> + data += 20;
> + *parent1 = data;
> + data += 20;
> + *parent2 = data;
> +
> + return 0;
> + }
> +
> + return -1;
> +}
I am torn on this one.
These cached properties of a single commit will not change no matter
which pack it appears in, and it feels logically wrong, especially
when you record these object names in the full SHA-1 form, to tie a
"commit metapack" to a pack. Logically there needs only one commit
metapack that describes all the commits known to the repository when
the metapack was created.
In order to reduce the disk footprint and I/O cost, the future
direction for this mechanism may want to point into an existing
store of SHA-1 hashes with a shorter file offset, and the .idx file
could be such a store, and in order to move in that direction, you
cannot avoid tying a metapack to a pack.
> +static void get_commits(struct metapack_writer *mw,
> + const unsigned char *sha1,
> + void *data)
> +{
> + struct commit_list ***tail = data;
> + enum object_type type = sha1_object_info(sha1, NULL);
> + struct commit *c;
> +
> + if (type != OBJ_COMMIT)
> + return;
> +
> + c = lookup_commit(sha1);
> + if (!c || parse_commit(c))
> + die("unable to read commit %s", sha1_to_hex(sha1));
> +
> + /*
> + * Our fixed-size parent list cannot represent root commits, nor
> + * octopus merges. Just skip those commits, as we can fallback
> + * in those rare cases to reading the actual commit object.
> + */
> + if (!c->parents ||
> + (c->parents && c->parents->next && c->parents->next->next))
> + return;
> +
> + *tail = &commit_list_insert(c, *tail)->next;
> +}
It feels somewhat wasteful to:
- use commit_list for this, rather than an array of commit
objects. If you have a rough estimate of the number of commits
in the pack, you could just preallocate a single array and use
ALLOC_GROW() on it, no?
- iterate over the .idx file and run sha1_object_info() and
parse_commit() on many objects in the SHA-1 order. Iterating in
the way builtin/pack-objects.c::get_object_details() does avoids
jumping around in existing packfiles, which may be more
efficient, no?
> +void commit_metapack_write(const char *idx)
> +{
> + struct metapack_writer mw;
> + struct commit_list *commits = NULL, *p;
> + struct commit_list **tail = &commits;
> + uint32_t nr = 0;
> +
> + metapack_writer_init(&mw, idx, "commits", 1);
> +
> + /* Figure out how many eligible commits we've got in this pack. */
> + metapack_writer_foreach(&mw, get_commits, &tail);
> + for (p = commits; p; p = p->next)
> + nr++;
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