Teach Git to add submodule ODBs as alternates to the object store of
the_repository only upon the first access of an object not in
the_repository, and not when add_submodule_odb() is called.
This provides a means of gradually migrating from accessing a
submodule's object through alternates to accessing a submodule's object
by explicitly passing its repository object. Any Git command can declare
that it might access submodule objects by calling add_submodule_odb()
(as they do now), but the submodule ODBs themselves will not be added
until needed, so individual commands and/or combinations of arguments
can be migrated one by one.
[The advantage of explicit repository-object passing is code clarity (it
is clear which repository an object read is from), performance (there is
no need to linearly search through all submodule ODBs whenever an object
is accessed from any repository, whether superproject or submodule), and
the possibility of future features like partial clone submodules (which
right now is not possible because if an object is missing, we do not
know which repository to lazy-fetch into).]
This commit also introduces an environment variable that a test may set
to make the actual registration of alternates fatal, in order to
demonstrate that its codepaths do not need this registration.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This will simplify referencing them from code that is not deeply integrated with
Git, in particular, the reftable library.
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Opening multiple instance of the same MIDX can lead to problems like two
separate packed_git structures which represent the same pack being added
to the repository's object store.
The above scenario can happen because prepare_midx_pack() checks if
`m->packs[pack_int_id]` is NULL in order to determine if a pack has been
opened and installed in the repository before. But a caller can
construct two copies of the same MIDX by calling get_multi_pack_index()
and load_multi_pack_index() since the former manipulates the
object store directly but the latter is a lower-level routine which
allocates a new MIDX for each call.
So if prepare_midx_pack() is called on multiple MIDXs with the same
pack_int_id, then that pack will be installed twice in the object
store's packed_git pointer.
This can lead to problems in, for e.g., the pack-bitmap code, which does
something like the following (in pack-bitmap.c:open_pack_bitmap()):
struct bitmap_index *bitmap_git = ...;
for (p = get_all_packs(r); p; p = p->next) {
if (open_pack_bitmap_1(bitmap_git, p) == 0)
ret = 0;
}
which is a problem if two copies of the same pack exist in the
packed_git list because pack-bitmap.c:open_pack_bitmap_1() contains a
conditional like the following:
if (bitmap_git->pack || bitmap_git->midx) {
/* ignore extra bitmap file; we can only handle one */
warning("ignoring extra bitmap file: %s", packfile->pack_name);
close(fd);
return -1;
}
Avoid this scenario by not letting write_midx_internal() open a MIDX
that isn't also pointed at by the object store. So long as this is the
case, other routines should prefer to open MIDXs with
get_multi_pack_index() or reprepare_packed_git() instead of creating
instances on their own. Because get_multi_pack_index() returns
`r->object_store->multi_pack_index` if it is non-NULL, we'll only have
one instance of a MIDX open at one time, avoiding these problems.
To encourage this, drop the `struct multi_pack_index *` parameter from
`write_midx_internal()`, and rely instead on the `object_dir` to find
(or initialize) the correct MIDX instance.
Likewise, replace the call to `close_midx()` with
`close_object_store()`, since we're about to replace the MIDX with a new
one and should invalidate the object store's memory of any MIDX that
might have existed beforehand.
Note that this now forbids passing object directories that don't belong
to alternate repositories over `--object-dir`, since before we would
have happily opened a MIDX in any directory, but now restrict ourselves
to only those reachable by `r->objects->multi_pack_index` (and alternate
MIDXs that we can see by walking the `next` pointer).
As far as I can tell, supporting arbitrary directories with
`--object-dir` was a historical accident, since even the documentation
says `<alt>` when referring to the value passed to this option.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Move the raceproof_create_file() API added to cache.h and
object-file.c in 177978f56a (raceproof_create_file(): new function,
2017-01-06) to its only user, refs/files-backend.c.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Build fix.
* cb/many-alternate-optim-fixup:
object-file: use unsigned arithmetic with bit mask
object-store: avoid extra ';' from KHASH_INIT
oidtree: avoid nested struct oidtree_node
33f379eee6 (make object_directory.loose_objects_subdir_seen a bitmap,
2021-07-07) replaced a wasteful 256-byte array with a 32-byte array
and bit operations. The mask calculation shifts a literal 1 of type
int left by anything between 0 and 31. UndefinedBehaviorSanitizer
doesn't like that and reports:
object-file.c:2477:18: runtime error: left shift of 1 by 31 places cannot be represented in type 'int'
Make sure to use an unsigned 1 instead to avoid the issue.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Optimization for repositories with many alternate object store.
* ew/many-alternate-optim:
oidtree: a crit-bit tree for odb_loose_cache
oidcpy_with_padding: constify `src' arg
make object_directory.loose_objects_subdir_seen a bitmap
avoid strlen via strbuf_addstr in link_alt_odb_entry
speed up alt_odb_usable() with many alternates
Prepare the internals for lazily fetching objects in submodules
from their promisor remotes.
* jt/partial-clone-submodule-1:
promisor-remote: teach lazy-fetch in any repo
run-command: refactor subprocess env preparation
submodule: refrain from filtering GIT_CONFIG_COUNT
promisor-remote: support per-repository config
repository: move global r_f_p_c to repo struct
This saves 8K per `struct object_directory', meaning it saves
around 800MB in my case involving 100K alternates (half or more
of those alternates are unlikely to hold loose objects).
This is implemented in two parts: a generic, allocation-free
`cbtree' and the `oidtree' wrapper on top of it. The latter
provides allocation using alloc_state as a memory pool to
improve locality and reduce free(3) overhead.
Unlike oid-array, the crit-bit tree does not require sorting.
Performance is bound by the key length, for oidtree that is
fixed at sizeof(struct object_id). There's no need to have
256 oidtrees to mitigate the O(n log n) overhead like we did
with oid-array.
Being a prefix trie, it is natively suited for expanding short
object IDs via prefix-limited iteration in
`find_short_object_filename'.
On my busy workstation, p4205 performance seems to be roughly
unchanged (+/-8%). Startup with 100K total alternates with no
loose objects seems around 10-20% faster on a hot cache.
(800MB in memory savings means more memory for the kernel FS
cache).
The generic cbtree implementation does impose some extra
overhead for oidtree in that it uses memcmp(3) on
"struct object_id" so it wastes cycles comparing 12 extra bytes
on SHA-1 repositories. I've not yet explored reducing this
overhead, but I expect there are many places in our code base
where we'd want to investigate this.
More information on crit-bit trees: https://cr.yp.to/critbit.html
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There's no point in using 8 bits per-directory when 1 bit
will do. This saves us 224 bytes per object directory, which
ends up being 22MB when dealing with 100K alternates.
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We can save a few milliseconds (across 100K odbs) by using
strbuf_addbuf() instead of strbuf_addstr() by passing `entry' as
a strbuf pointer rather than a "const char *".
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
With many alternates, the duplicate check in alt_odb_usable()
wastes many cycles doing repeated fspathcmp() on every existing
alternate. Use a khash to speed up lookups by odb->path.
Since the kh_put_* API uses the supplied key without
duplicating it, we also take advantage of it to replace both
xstrdup() and strbuf_release() in link_alt_odb_entry() with
strbuf_detach() to avoid the allocation and copy.
In a test repository with 50K alternates and each of those 50K
alternates having one alternate each (for a total of 100K total
alternates); this speeds up lookup of a non-existent blob from
over 16 minutes to roughly 2.7 seconds on my busy workstation.
Note: all underlying git object directories were small and
unpacked with only loose objects and no packs. Having to load
packs increases times significantly.
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Linux users may benefit from additional information on how to
avoid ENOMEM from mmap despite the system having enough RAM to
accomodate them. We can't reliably unmap pack windows to work
around the issue since malloc and other library routines may
mmap without our knowledge.
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is one step towards supporting partial clone submodules.
Even after this patch, we will still lack partial clone submodules
support, primarily because a lot of Git code that accesses submodule
objects does so by adding their object stores as alternates, meaning
that any lazy fetches that would occur in the submodule would be done
based on the config of the superproject, not of the submodule. This also
prevents testing of the functionality in this patch by user-facing
commands. So for now, test this mechanism using a test helper.
Besides that, there is some code that uses the wrapper functions
like has_promisor_remote(). Those will need to be checked to see if they
could support the non-wrapper functions instead (and thus support any
repository, not just the_repository).
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git clean" and "git ls-files -i" had confusion around working on
or showing ignored paths inside an ignored directory, which has
been corrected.
* en/dir-traversal:
dir: introduce readdir_skip_dot_and_dotdot() helper
dir: update stale description of treat_directory()
dir: traverse into untracked directories if they may have ignored subfiles
dir: avoid unnecessary traversal into ignored directory
t3001, t7300: add testcase showcasing missed directory traversal
t7300: add testcase showing unnecessary traversal into ignored directory
ls-files: error out on -i unless -o or -c are specified
dir: report number of visited directories and paths with trace2
dir: convert trace calls to trace2 equivalents
Many places in the code were doing
while ((d = readdir(dir)) != NULL) {
if (is_dot_or_dotdot(d->d_name))
continue;
...process d...
}
Introduce a readdir_skip_dot_and_dotdot() helper to make that a one-liner:
while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
...process d...
}
This helper particularly simplifies checks for empty directories.
Also use this helper in read_cached_dir() so that our statistics are
consistent across platforms. (In other words, read_cached_dir() should
have been using is_dot_or_dotdot() and skipping such entries, but did
not and left it to treat_path() to detect and mark such entries as
path_none.)
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Up until recently, object IDs did not have an algorithm member, only a
hash. Consequently, it was possible to share one null (all-zeros)
object ID among all hash algorithms. Now that we're going to be
handling objects from multiple hash algorithms, it's important to make
sure that all object IDs have a correct algorithm field.
Introduce a per-algorithm null OID, and add it to struct hash_algo.
Introduce a wrapper function as well, and use it everywhere we used to
use the null_oid constant.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that struct object_id has an algorithm field, we should populate it.
This will allow us to handle object IDs in any supported algorithm and
distinguish between them. Ensure that the field is written whenever we
write an object ID by storing it explicitly every time we write an
object. Set values for the empty blob and tree values as well.
In addition, use the algorithm field to compare object IDs. Note that
because we zero-initialize struct object_id in many places throughout
the codebase, we default to the default algorithm in cases where the
algorithm field is zero rather than explicitly initialize all of those
locations.
This leads to a branch on every comparison, but the alternative is to
compare the entire buffer each time and padding the buffer for SHA-1.
That alternative ranges up to 3.9% worse than this approach on the perf
t0001, t1450, and t1451.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we're hashing a value which is going to be an object ID, we want to
zero-pad that value if necessary. To do so, use the final_oid_fn
instead of the final_fn anytime we're going to create an object ID to
ensure we perform this operation.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To avoid the penalty of having to branch in hash comparison functions,
we'll want to always compare the full hash member in a struct object_id,
which will require that SHA-1 object IDs be zero-padded. To do so, add
a function which finalizes a hash context and writes it into an object
ID that performs this padding.
Move the definition of struct object_id and the constant definitions
higher up so we they are available for us to use.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add and apply a semantic patch for converting code that open-codes
CALLOC_ARRAY to use it instead. It shortens the code and infers the
element size automatically.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Change all remnants of "sha1" in hash-lookup.c and .h and rename them to
reflect that we're not just able to handle SHA-1 these days.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Drop the last remnant of "sha1" in this file and rename it to reflect
that we're not just able to handle SHA-1 these days.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
