GIt 2.44 introduced a regression that makes the updated code to
barf in repositories with multi-pack index written by older
versions of Git, which has been corrected.
* ps/missing-btmp-fix:
pack-bitmap: gracefully handle missing BTMP chunks
In 0fea6b73f1 (Merge branch 'tb/multi-pack-verbatim-reuse', 2024-01-12)
we have introduced multi-pack verbatim reuse of objects. This series has
introduced a new BTMP chunk, which encodes information about bitmapped
objects in the multi-pack index. Starting with dab60934e3 (pack-bitmap:
pass `bitmapped_pack` struct to pack-reuse functions, 2023-12-14) we use
this information to figure out objects which we can reuse from each of
the packfiles.
One thing that we glossed over though is backwards compatibility with
repositories that do not yet have BTMP chunks in their multi-pack index.
In that case, `nth_bitmapped_pack()` would return an error, which causes
us to emit a warning followed by another error message. These warnings
are visible to users that fetch from a repository:
```
$ git fetch
...
remote: error: MIDX does not contain the BTMP chunk
remote: warning: unable to load pack: 'pack-f6bb7bd71d345ea9fe604b60cab9ba9ece54ffbe.idx', disabling pack-reuse
remote: Enumerating objects: 40, done.
remote: Counting objects: 100% (40/40), done.
remote: Compressing objects: 100% (39/39), done.
remote: Total 40 (delta 5), reused 0 (delta 0), pack-reused 0 (from 0)
...
```
While the fetch succeeds the user is left wondering what they did wrong.
Furthermore, as visible both from the warning and from the reuse stats,
pack-reuse is completely disabled in such repositories.
What is quite interesting is that this issue can even be triggered in
case `pack.allowPackReuse=single` is set, which is the default value.
One could have expected that in this case we fall back to the old logic,
which is to use the preferred packfile without consulting BTMP chunks at
all. But either we fail with the above error in case they are missing,
or we use the first pack in the multi-pack-index. The former case
disables pack-reuse altogether, whereas the latter case may result in
reusing objects from a suboptimal packfile.
Fix this issue by partially reverting the logic back to what we had
before this patch series landed. Namely, in the case where we have no
BTMP chunks or when `pack.allowPackReuse=single` are set, we use the
preferred pack instead of consulting the BTMP chunks.
Helped-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This variable is no longer used for doing verbatim pack-reuse (or
anywhere within pack-bitmap.c) since d2ea031046 (pack-bitmap: don't rely
on bitmap_git->reuse_objects, 2019-12-18).
Remove it to avoid an unused struct member.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that both the pack-bitmap and pack-objects code are prepared to
handle marking and using objects from multiple bitmapped packs for
verbatim reuse, allow marking objects from all bitmapped packs as
eligible for reuse.
Within the `reuse_partial_packfile_from_bitmap()` function, we no longer
only mark the pack whose first object is at bit position zero for reuse,
and instead mark any pack contained in the MIDX as a reuse candidate.
Provide a handful of test cases in a new script (t5332) exercising
interesting behavior for multi-pack reuse to ensure that we performed
all of the previous steps correctly.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that the pack-objects code is equipped to handle reusing objects
from multiple packs, prepare the pack-bitmap code to mark objects from
multiple packs as reuse candidates.
In order to prepare the pack-bitmap code for this change, remove the
same set of assumptions we unwound in previous commits from the helper
function `reuse_partial_packfile_from_bitmap_1()`, in preparation for it
to be called in a loop over the set of bitmapped packs in a following
commit.
Most importantly, we can no longer assume that the bit position
corresponding to the first object in a given reuse pack candidate is at
the beginning of the bitmap itself.
For the single pack that this assumption is still true for (in MIDX
bitmaps, this is the preferred pack, in single-pack bitmaps it is the
pack the bitmap is tied to), we can still use our whole-words
optimization.
But for all subsequent packs, we can not make use of this optimization,
since it assumes that all delta bases are being sent from the same pack,
which would break if we are sending OFS_DELTAs down to the client. To
understand why, consider two packs, P1 and P2 where:
- P1 has object A which is a delta on base B
- P2 has its own copy of B, in addition to other objects
Suppose that the MIDX which covers P1 and P2 selected its copy of A from
P1, but selected its copy of B from P2. Since A is a delta of B, but the
base was selected from a different pack, sending the bytes corresponding
to A as an OFS_DELTA verbatim from P1 would be incorrect, since we don't
guarantee that B is in the same place relative to A in the generated
pack as in P1.
For now, we detect and reject these cross-pack deltas by searching for
the (pack_id, offset) pair for the delta's base object (using the same
pack_id as the pack containing the delta'd object) in the MIDX. If we
find a match, that means that the MIDX did indeed pick the base object
from the same pack, and we are OK to reuse the delta.
If we don't find a match, however, that means that the base object was
selected from a different pack in the MIDX, and we can let the slower
path handle re-delta'ing our candidate object.
In the future, there are a couple of other things we could do, namely:
- Turn any cross-pack deltas (which are stored as OFS_DELTAs) into
REF_DELTAs. We already do this today when reusing an OFS_DELTA
without `--delta-base-offset` enabled, so it's not a huge stretch to
do the same for cross-pack deltas even when `--delta-base-offset` is
enabled.
This would work, but would obviously result in larger-than-necessary
packs, as we in theory *could* represent these cross-pack deltas by
patching an existing OFS_DELTA. But it's not clear how much that
would matter in practice. I suspect it would have a lot to do with
how you pack your repository in the first place.
- Finally, we could patch OFS_DELTAs across packs in a similar fashion
as we do today for OFS_DELTAs within a single pack on either side of
a gap. This would result in the smallest packs of the three options
here, but implementing this would be more involved.
At minimum, you'd have to keep the reusable chunks list for all
reused packs, not just the one we're currently processing. And you'd
have to ensure that any bases which are a part of cross-pack deltas
appear before the delta. I think this is possible to do, but would
require assembling the reusable chunks list potentially in a
different order than they appear in the source packs.
For now, let's pursue the simplest approach and reject any cross-pack
deltas.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When performing a binary search over the objects in a MIDX's bitmap
(i.e. in pseudo-pack order), the reader reconstructs the pseudo-pack
ordering using a combination of (a) the preferred pack, (b) the pack's
lexical position in the MIDX based on pack names, and (c) the object
offset within the pack.
In order to perform this binary search, the reader must know the
identity of the preferred pack. This could be stored in the MIDX, but
isn't for historical reasons, mostly because it can easily be inferred
at read-time by looking at the object in the first bit position and
finding out which pack it was selected from in the MIDX, like so:
nth_midxed_pack_int_id(m, pack_pos_to_midx(m, 0));
In midx_to_pack_pos() which performs this binary search, we look up the
identity of the preferred pack before each search. This is relatively
quick, since it involves two table-driven lookups (one in the MIDX's
revindex for `pack_pos_to_midx()`, and another in the MIDX's object
table for `nth_midxed_pack_int_id()`).
But since the preferred pack does not change after the MIDX is written,
it is safe to cache this value on the MIDX itself.
Write a helper to do just that, and rewrite all of the existing
call-sites that care about the identity of the preferred pack in terms
of this new helper.
This will prepare us for a subsequent patch where we will need to binary
search through the MIDX's pseudo-pack order multiple times.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Further prepare for enabling verbatim pack-reuse over multiple packfiles
by changing the signature of reuse_partial_packfile_from_bitmap() to
populate an array of `struct bitmapped_pack *`'s instead of a pointer to
a single packfile.
Since the array we're filling out is sized dynamically[^1], add an
additional `size_t *` parameter which will hold the number of reusable
packs (equal to the number of elements in the array).
Note that since we still have not implemented true multi-pack reuse,
these changes aren't propagated out to the rest of the caller in
builtin/pack-objects.c.
In the interim state, we expect that the array has a single element, and
we use that element to fill out the static `reuse_packfile` variable
(which is a bog-standard `struct packed_git *`). Future commits will
continue to push this change further out through the pack-objects code.
[^1]: That is, even though we know the number of packs which are
candidates for pack-reuse, we do not know how many of those
candidates we can actually reuse.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The signature of `reuse_partial_packfile_from_bitmap()` currently takes
in a bitmap, as well as three output parameters (filled through
pointers, and passed as arguments), and also returns an integer result.
The output parameters are filled out with: (a) the packfile used for
pack-reuse, (b) the number of objects from that pack that we can reuse,
and (c) a bitmap indicating which objects we can reuse. The return value
is either -1 (when there are no objects to reuse), or 0 (when there is
at least one object to reuse).
Some of these parameters are redundant. Notably, we can infer from the
bitmap how many objects are reused by calling bitmap_popcount(). And we
can similar compute the return value based on that number as well.
As such, clean up the signature of this function to drop the "*entries"
parameter, as well as the int return value, since the single caller of
this function can infer these values themself.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When trying to assemble a pack with bitmaps using `--use-bitmap-index`,
`pack-objects` asks the pack-bitmap machinery for a bitmap which
indicates the set of objects we can "reuse" verbatim from on-disk.
This set is roughly comprised of: a prefix of objects in the bitmapped
pack (or preferred pack, in the case of a multi-pack reachability
bitmap), plus any other objects not included in the prefix, excluding
any deltas whose base we are not sending in the resulting pack.
The pack-bitmap machinery is responsible for computing this bitmap, and
does so with the following functions:
- reuse_partial_packfile_from_bitmap()
- try_partial_reuse()
In the existing implementation, the first function is responsible for
(a) marking the prefix of objects in the reusable pack, and then (b)
calling try_partial_reuse() on any remaining objects to ensure that they
are also reusable (and removing them from the bitmapped set if they are
not).
Likewise, the `try_partial_reuse()` function is responsible for checking
whether an isolated object (that is, an object from the bitmapped
pack/preferred pack not contained in the prefix from earlier) may be
reused, i.e. that it isn't a delta of an object that we are not sending
in the resulting pack.
These functions are based on two core assumptions, which we will unwind
in this and the following commits:
1. There is only a single pack from the bitmap which is eligible for
verbatim pack-reuse. For single-pack bitmaps, this is trivially the
bitmapped pack. For multi-pack bitmaps, this is (currently) the
MIDX's preferred pack.
2. The pack eligible for reuse has its first object in bit position 0,
and all objects from that pack follow in pack-order from that first
bit position.
In order to perform verbatim pack reuse over multiple packs, we must
unwind these two assumptions. Most notably, in order to reuse bits from
a given packfile, we need to know the first bit position occupied by
an object form that packfile. To propagate this information around, pass
a `struct bitmapped_pack *` anywhere we previously passed a `struct
packed_git *`, since the former contains the bitmap position we're
interested in (as well as a pointer to the latter).
As an additional step, factor out a sub-routine from the main
`reuse_partial_packfile_from_bitmap()` function, called
`reuse_partial_packfile_from_bitmap_1()`. This new function will be
responsible for figuring out which objects may be reused from a single
pack, and the existing function will dispatch multiple calls to its new
helper function for each reusable pack.
Consequently, `reuse_partial_packfile_from_bitmap()` will now maintain
an array of reusable packs instead of a single such pack. We currently
expect that array to have only a single element, so this awkward state
is short-lived. It will serve as useful scaffolding in subsequent
commits as we begin to work towards enabling multi-pack reuse.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `find_objects()` function creates an object_list for any tips of the
reachability query which do not have corresponding bitmaps.
The object_list is not used outside of `find_objects()`, but we never
free it with `object_list_free()`, resulting in a leak. Let's plug that
leak by calling `object_list_free()`, which results in t6113 becoming
leak-free.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git rev-list --unpacked --objects" failed to exclude packed
non-commit objects, which has been corrected.
* tb/rev-list-unpacked-fix:
pack-bitmap: drop --unpacked non-commit objects from results
list-objects: drop --unpacked non-commit objects from results
When performing revision queries with `--objects` and
`--use-bitmap-index`, the output may incorrectly contain objects which
are packed, even when the `--unpacked` option is given. This affects
traversals, but also other querying operations, like `--count`,
`--disk-usage`, etc.
Like in the previous commit, the fix is to exclude those objects from
the result set before they are shown to the user (or, in this case,
before the bitmap containing the result of the traversal is enumerated
and its objects listed).
This is performed by a new function in pack-bitmap.c, called
`filter_packed_objects_from_bitmap()`. Note that we do not have to
inspect individual bits in the result bitmap, since we know that the
first N (where N is the number of objects in the bitmap's pack/MIDX)
bits correspond to objects which packed by definition.
In other words, for an object to have a bitmap position (not in the
extended index), it must appear in either the bitmap's pack or one of
the packs in its MIDX.
This presents an appealing optimization to us, which is that we can
simply memset() the corresponding number of `eword_t`'s to zero,
provided that we handle any objects which spill into the next word (but
don't occupy all 64 bits of the word itself).
We only have to handle objects in the bitmap's extended index. These
objects may (or may not) appear in one or more pack(s). Since these
objects are known to not appear in either the bitmap's MIDX or pack,
they may be stored as loose, appear in other pack(s), or both.
Before returning a bitmap containing the result of the traversal back to
the caller, drop any bits from the extended index which appear in one or
more packs. This implements the correct behavior for rev-list operations
which use the bitmap index to compute their result.
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is similar to the cases in c50dca2a18 (list-objects: mark unused
callback parameters, 2023-02-24), but was added after that commit.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Various offset computation in the code that accesses the packfiles
and other data in the object layer has been hardened against
arithmetic overflow, especially on 32-bit systems.
* tb/object-access-overflow-protection:
commit-graph.c: prevent overflow in `verify_commit_graph()`
commit-graph.c: prevent overflow in `write_commit_graph()`
commit-graph.c: prevent overflow in `merge_commit_graph()`
commit-graph.c: prevent overflow in `split_graph_merge_strategy()`
commit-graph.c: prevent overflow in `load_tree_for_commit()`
commit-graph.c: prevent overflow in `fill_commit_in_graph()`
commit-graph.c: prevent overflow in `fill_commit_graph_info()`
commit-graph.c: prevent overflow in `load_oid_from_graph()`
commit-graph.c: prevent overflow in add_graph_to_chain()
commit-graph.c: prevent overflow in `write_commit_graph_file()`
pack-bitmap.c: ensure that eindex lookups don't overflow
midx.c: prevent overflow in `fill_included_packs_batch()`
midx.c: prevent overflow in `write_midx_internal()`
midx.c: store `nr`, `alloc` variables as `size_t`'s
midx.c: prevent overflow in `nth_midxed_offset()`
midx.c: prevent overflow in `nth_midxed_object_oid()`
midx.c: use `size_t`'s for fanout nr and alloc
packfile.c: use checked arithmetic in `nth_packed_object_offset()`
packfile.c: prevent overflow in `load_idx()`
packfile.c: prevent overflow in `nth_packed_object_id()`
When a bitmap is used to answer some reachability query, it creates a
pseudo-bitmap called the "extended index" on top of any existing bitmaps
to store objects that are relevant to the query, but not mentioned in
the bitmap.
When looking up the ith object in the extended index in a bitmap, it is
common to write something like:
bitmap_get(result, i + bitmap_num_objects(bitmap_git))
, indicating that we want the ith object following all other objects
mentioned in the bitmap_git.
Since the type of `i` and the return type of `bitmap_num_objects()` are
both `uint32_t`s, But if there are either a large number of objects in
the bitmap, or a large number of objects in the extended index (or
both), this addition can overflow when the sum is greater than 2^32-1.
Having that large of a bitmap position is entirely acceptable, but we
need to ensure that the computed bitmap position for that object is
performed using 64-bits and doesn't overflow.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
alloc_nr, ALLOC_GROW, and ALLOC_GROW_BY are commonly used macros for
dynamic array allocation. Moving these macros to git-compat-util.h with
the other alloc macros focuses alloc.[ch] to allocation for Git objects
and additionally allows us to remove inclusions to alloc.h from files
that solely used the above macros.
Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Header files cleanup.
* en/header-split-cache-h-part-3: (28 commits)
fsmonitor-ll.h: split this header out of fsmonitor.h
hash-ll, hashmap: move oidhash() to hash-ll
object-store-ll.h: split this header out of object-store.h
khash: name the structs that khash declares
merge-ll: rename from ll-merge
git-compat-util.h: remove unneccessary include of wildmatch.h
builtin.h: remove unneccessary includes
list-objects-filter-options.h: remove unneccessary include
diff.h: remove unnecessary include of oidset.h
repository: remove unnecessary include of path.h
log-tree: replace include of revision.h with simple forward declaration
cache.h: remove this no-longer-used header
read-cache*.h: move declarations for read-cache.c functions from cache.h
repository.h: move declaration of the_index from cache.h
merge.h: move declarations for merge.c from cache.h
diff.h: move declaration for global in diff.c from cache.h
preload-index.h: move declarations for preload-index.c from elsewhere
sparse-index.h: move declarations for sparse-index.c from cache.h
name-hash.h: move declarations for name-hash.c from cache.h
run-command.h: move declarations for run-command.c from cache.h
...
Gracefully deal with a stale MIDX file that lists a packfile that
no longer exists.
* tb/open-midx-bitmap-fallback:
pack-bitmap.c: gracefully degrade on failure to load MIDX'd pack
The object traversal using reachability bitmap done by
"pack-object" has been tweaked to take advantage of the fact that
using "boundary" commits as representative of all the uninteresting
ones can save quite a lot of object enumeration.
* tb/pack-bitmap-traversal-with-boundary:
pack-bitmap.c: use commit boundary during bitmap traversal
pack-bitmap.c: extract `fill_in_bitmap()`
object: add object_array initializer helper function
The vast majority of files including object-store.h did not need dir.h
nor khash.h. Split the header into two files, and let most just depend
upon object-store-ll.h, while letting the two callers that need it
depend on the full object-store.h.
After this patch:
$ git grep -h include..object-store | sort | uniq -c
2 #include "object-store.h"
129 #include "object-store-ll.h"
Diff best viewed with `--color-moved`.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When opening a MIDX bitmap, we the pack-bitmap machinery eagerly calls
`prepare_midx_pack()` on each of the packs contained in the MIDX. This
is done in order to populate the array of `struct packed_git *`s held by
the MIDX, which we need later on in `load_reverse_index()`, since it
calls `load_pack_revindex()` on each of the MIDX'd packs, and requires
that the caller provide a pointer to a `struct packed_git`.
When opening one of these packs fails, the pack-bitmap code will `die()`
indicating that it can't open one of the packs in the MIDX. This
indicates that the MIDX is somehow broken with respect to the current
state of the repository. When this is the case, we indeed cannot make
use of the MIDX bitmap to speed up reachability traversals.
However, it does not mean that we can't perform reachability traversals
at all. In other failure modes, that same function calls `warning()` and
then returns -1, indicating to its caller (`open_bitmap()`) that we
should either look for a pack bitmap if one is available, or perform
normal object traversal without using bitmaps at all.
There is no reason why this case should cause us to die. If we instead
continued (by jumping to `cleanup` as this patch does) and avoid using
bitmaps altogether, we may again try and query the MIDX, which will also
fail. But when trying to call `fill_midx_entry()` fails, it also returns
a signal of its failure, and prompts the caller to try and locate the
object elsewhere.
In other words, the normal object traversal machinery works fine in the
presence of a corrupt MIDX, so there is no reason that the MIDX bitmap
machinery should abort in that case when we could easily continue.
Note that we *could* in theory try again to load a MIDX bitmap after
calling `reprepare_packed_git()`. Even though the `prepare_packed_git()`
code is careful to avoid adding a pack that we already have,
`prepare_midx_pack()` is not. So if we got part of the way through
calling `prepare_midx_pack()` on a stale MIDX, and then tried again on a
fresh MIDX that contains some of the same packs, we would end up with a
loop through the `->next` pointer.
For now, let's do the simplest thing possible and fallback to the
non-bitmap code when we detect a stale MIDX so that the complete fix as
above can be implemented carefully.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When reachability bitmap coverage exists in a repository, Git will use a
different (and hopefully faster) traversal to compute revision walks.
Consider a set of positive and negative tips (which we'll refer to with
their standard bitmap parlance by "wants", and "haves"). In order to
figure out what objects exist between the tips, the existing traversal
in `prepare_bitmap_walk()` does something like:
1. Consider if we can even compute the set of objects with bitmaps,
and fall back to the usual traversal if we cannot. For example,
pathspec limiting traversals can't be computed using bitmaps (since
they don't know which objects are at which paths). The same is true
of certain kinds of non-trivial object filters.
2. If we can compute the traversal with bitmaps, partition the
(dereferenced) tips into two object lists, "haves", and "wants",
based on whether or not the objects have the UNINTERESTING flag,
respectively.
3. Fall back to the ordinary object traversal if either (a) there are
more than zero haves, none of which are in the bitmapped pack or
MIDX, or (b) there are no wants.
4. Construct a reachability bitmap for the "haves" side by walking
from the revision tips down to any existing bitmaps, OR-ing in any
bitmaps as they are found.
5. Then do the same for the "wants" side, stopping at any objects that
appear in the "haves" bitmap.
6. Filter the results if any object filter (that can be easily
computed with bitmaps alone) was given, and then return back to the
caller.
When there is good bitmap coverage relative to the traversal tips, this
walk is often significantly faster than an ordinary object traversal
because it can visit far fewer objects.
But in certain cases, it can be significantly *slower* than the usual
object traversal. Why? Because we need to compute complete bitmaps on
either side of the walk. If either one (or both) of the sides require
walking many (or all!) objects before they get to an existing bitmap,
the extra bitmap machinery is mostly or all overhead.
One of the benefits, however, is that even if the walk is slower, bitmap
traversals are guaranteed to provide an *exact* answer. Unlike the
traditional object traversal algorithm, which can over-count the results
by not opening trees for older commits, the bitmap walk builds an exact
reachability bitmap for either side, meaning the results are never
over-counted.
But producing non-exact results is OK for our traversal here (both in
the bitmap case and not), as long as the results are over-counted, not
under.
Relaxing the bitmap traversal to allow it to produce over-counted
results gives us the opportunity to make some significant improvements.
Instead of the above, the new algorithm only has to walk from the
*boundary* down to the nearest bitmap, instead of from each of the
UNINTERESTING tips.
The boundary-based approach still has degenerate cases, but we'll show
in a moment that it is often a significant improvement.
The new algorithm works as follows:
1. Build a (partial) bitmap of the haves side by first OR-ing any
bitmap(s) that already exist for UNINTERESTING commits between the
haves and the boundary.
2. For each commit along the boundary, add it as a fill-in traversal
tip (where the traversal terminates once an existing bitmap is
found), and perform fill-in traversal.
3. Build up a complete bitmap of the wants side as usual, stopping any
time we intersect the (partial) haves side.
4. Return the results.
And is more-or-less equivalent to using the *old* algorithm with this
invocation:
$ git rev-list --objects --use-bitmap-index $WANTS --not \
$(git rev-list --objects --boundary $WANTS --not $HAVES |
perl -lne 'print $1 if /^-(.*)/')
The new result performs significantly better in many cases, particularly
when the distance from the boundary commit(s) to an existing bitmap is
shorter than the distance from (all of) the have tips to the nearest
bitmapped commit.
Note that when using the old bitmap traversal algorithm, the results can
be *slower* than without bitmaps! Under the new algorithm, the result is
computed faster with bitmaps than without (at the cost of over-counting
the true number of objects in a similar fashion as the non-bitmap
traversal):
# (Computing the number of tagged objects not on any branches
# without bitmaps).
$ time git rev-list --count --objects --tags --not --branches
20
real 0m1.388s
user 0m1.092s
sys 0m0.296s
# (Computing the same query using the old bitmap traversal).
$ time git rev-list --count --objects --tags --not --branches --use-bitmap-index
19
real 0m22.709s
user 0m21.628s
sys 0m1.076s
# (this commit)
$ time git.compile rev-list --count --objects --tags --not --branches --use-bitmap-index
19
real 0m1.518s
user 0m1.234s
sys 0m0.284s
The new algorithm is still slower than not using bitmaps at all, but it
is nearly a 15-fold improvement over the existing traversal.
In a more realistic setting (using my local copy of git.git), I can
observe a similar (if more modest) speed-up:
$ argv="--count --objects --branches --not --tags"
hyperfine \
-n 'no bitmaps' "git.compile rev-list $argv" \
-n 'existing traversal' "git.compile rev-list --use-bitmap-index $argv" \
-n 'boundary traversal' "git.compile -c pack.useBitmapBoundaryTraversal=true rev-list --use-bitmap-index $argv"
Benchmark 1: no bitmaps
Time (mean ± σ): 124.6 ms ± 2.1 ms [User: 103.7 ms, System: 20.8 ms]
Range (min … max): 122.6 ms … 133.1 ms 22 runs
Benchmark 2: existing traversal
Time (mean ± σ): 368.6 ms ± 3.0 ms [User: 325.3 ms, System: 43.1 ms]
Range (min … max): 365.1 ms … 374.8 ms 10 runs
Benchmark 3: boundary traversal
Time (mean ± σ): 167.6 ms ± 0.9 ms [User: 139.5 ms, System: 27.9 ms]
Range (min … max): 166.1 ms … 169.2 ms 17 runs
Summary
'no bitmaps' ran
1.34 ± 0.02 times faster than 'boundary traversal'
2.96 ± 0.05 times faster than 'existing traversal'
Here, the new algorithm is also still slower than not using bitmaps, but
represents a more than 2-fold improvement over the existing traversal in
a more modest example.
Since this algorithm was originally written (nearly a year and a half
ago, at the time of writing), the bitmap lookup table shipped, making
the new algorithm's result more competitive. A few other future
directions for improving bitmap traversal times beyond not using bitmaps
at all:
- Decrease the cost to decompress and OR together many bitmaps
together (particularly when enumerating the uninteresting side of
the walk). Here we could explore more efficient bitmap storage
techniques, like Roaring+Run and/or use SIMD instructions to speed
up ORing them together.
- Store pseudo-merge bitmaps, which could allow us to OR together
fewer "summary" bitmaps (which would also help with the above).
Helped-by: Jeff King <peff@peff.net>
Helped-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To prepare for the boundary-based bitmap walk to perform a fill-in
traversal using the boundary of either side as the tips, extract routine
used to perform fill-in traversal by `find_objects()` so that it can be
used in both places.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If a filesystem-level corruption occurs in a .bitmap file, Git can react
poorly. This could take the form of a run-time error due to failing to
parse an EWAH bitmap or be more subtle such as returning the wrong set
of objects to a fetch or clone.
A natural first response to either of these kinds of errors is to run
'git fsck' to see if any files are corrupt. This currently ignores all
.bitmap files.
Add checks to 'git fsck' for all .bitmap files that are currently
associated with a multi-pack-index or pack file. Verify their checksums
using the hashfile API.
We iterate through all multi-pack-indexes and pack-files to be sure to
check all .bitmap files, not just the one that would be read by the
process. For example, a multi-pack-index bitmap overrules a pack-bitmap.
However, if the multi-pack-index is removed, the pack-bitmap may be
selected instead. Be thorough to include every file that could become
active in such a way. This includes checking files in alternates.
There is potential that we could extend this effort to check the
structure of the reachability bitmaps themselves, but it is very
expensive to do so. At minimum, it's as expensive as generating the
bitmaps in the first place, and that's assuming that we don't use the
trivial algorithm of verifying each bitmap individually. The trivial
algorithm will result in quadratic behavior (number of objects times
number of bitmapped commits) while the bitmap building operation
constructs a lattice of commits to build bitmaps incrementally and then
generate the final bitmaps from a subset of those commits.
If we were to extend 'git fsck' to check .bitmap file contents more
closely like this, then we would likely want to hide it behind an option
that signals the user is more willing to do expensive operations such as
this.
For testing, set up a repository with a pack-bitmap _and_ a
multi-pack-index bitmap. This requires some file movement to avoid
deleting the pack-bitmap during the repack that creates the
multi-pack-index bitmap. We can then verify that 'git fsck' is checking
all files, not just the "active" bitmap.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The on-disk reverse index that allows mapping from the pack offset
to the object name for the object stored at the offset has been
enabled by default.
* tb/pack-revindex-on-disk:
t: invert `GIT_TEST_WRITE_REV_INDEX`
config: enable `pack.writeReverseIndex` by default
pack-revindex: introduce `pack.readReverseIndex`
pack-revindex: introduce GIT_TEST_REV_INDEX_DIE_ON_DISK
pack-revindex: make `load_pack_revindex` take a repository
t5325: mark as leak-free
pack-write.c: plug a leak in stage_tmp_packfiles()
Header clean-up.
* en/header-split-cache-h: (24 commits)
protocol.h: move definition of DEFAULT_GIT_PORT from cache.h
mailmap, quote: move declarations of global vars to correct unit
treewide: reduce includes of cache.h in other headers
treewide: remove double forward declaration of read_in_full
cache.h: remove unnecessary includes
treewide: remove cache.h inclusion due to pager.h changes
pager.h: move declarations for pager.c functions from cache.h
treewide: remove cache.h inclusion due to editor.h changes
editor: move editor-related functions and declarations into common file
treewide: remove cache.h inclusion due to object.h changes
object.h: move some inline functions and defines from cache.h
treewide: remove cache.h inclusion due to object-file.h changes
object-file.h: move declarations for object-file.c functions from cache.h
treewide: remove cache.h inclusion due to git-zlib changes
git-zlib: move declarations for git-zlib functions from cache.h
treewide: remove cache.h inclusion due to object-name.h changes
object-name.h: move declarations for object-name.c functions from cache.h
treewide: remove unnecessary cache.h inclusion
treewide: be explicit about dependence on mem-pool.h
treewide: be explicit about dependence on oid-array.h
...
While parsing a .rev file, we check the header information to be sure it
makes sense. This happens before doing any additional validation such as
a checksum or value check. In order to differentiate between a bad
header and a non-existent file, we need to update the API for loading a
reverse index.
Make load_pack_revindex_from_disk() non-static and specify that a
positive value means "the file does not exist" while other errors during
parsing are negative values. Since an invalid header prevents setting up
the structures we would use for further validations, we can stop at that
point.
The place where we can distinguish between a missing file and a corrupt
file is inside load_revindex_from_disk(), which is used both by pack
rev-indexes and multi-pack-index rev-indexes. Some tests in t5326
demonstrate that it is critical to take some conditions to allow
positive error signals.
Add tests that check the three header values.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In a future commit, we will introduce a `pack.readReverseIndex`
configuration, which forces Git to generate the reverse index from
scratch instead of loading it from disk.
In order to avoid reading this configuration value more than once, we'll
use the `repo_settings` struct to lazily load this value.
In order to access the `struct repo_settings`, add a repository argument
to `load_pack_revindex`, and update all callers to pass the correct
instance (in all cases, `the_repository`).
In certain instances, a new function-local variable is introduced to
take the place of a `struct repository *` argument to the function
itself to avoid propagating the new parameter even further throughout
the tree.
Co-authored-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Acked-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Dozens of files made use of trace and trace2 functions, without
explicitly including trace.h or trace2.h. This made it more difficult
to find which files could remove a dependence on cache.h. Make C files
explicitly include trace.h or trace2.h if they are using them.
Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Split key function and data structure definitions out of cache.h to
new header files and adjust the users.
* en/header-split-cleanup:
csum-file.h: remove unnecessary inclusion of cache.h
write-or-die.h: move declarations for write-or-die.c functions from cache.h
treewide: remove cache.h inclusion due to setup.h changes
setup.h: move declarations for setup.c functions from cache.h
treewide: remove cache.h inclusion due to environment.h changes
environment.h: move declarations for environment.c functions from cache.h
treewide: remove unnecessary includes of cache.h
wrapper.h: move declarations for wrapper.c functions from cache.h
path.h: move function declarations for path.c functions from cache.h
cache.h: remove expand_user_path()
abspath.h: move absolute path functions from cache.h
environment: move comment_line_char from cache.h
treewide: remove unnecessary cache.h inclusion from several sources
treewide: remove unnecessary inclusion of gettext.h
treewide: be explicit about dependence on gettext.h
treewide: remove unnecessary cache.h inclusion from a few headers
Assorted config API updates.
* ab/config-multi-and-nonbool:
for-each-repo: with bad config, don't conflate <path> and <cmd>
config API: add "string" version of *_value_multi(), fix segfaults
config API users: test for *_get_value_multi() segfaults
for-each-repo: error on bad --config
config API: have *_multi() return an "int" and take a "dest"
versioncmp.c: refactor config reading next commit
config API: add and use a "git_config_get()" family of functions
config tests: add "NULL" tests for *_get_value_multi()
config tests: cover blind spots in git_die_config() tests
Fix numerous and mostly long-standing segfaults in consumers of
the *_config_*value_multi() API. As discussed in the preceding commit
an empty key in the config syntax yields a "NULL" string, which these
users would give to strcmp() (or similar), resulting in segfaults.
As this change shows, most users users of the *_config_*value_multi()
API didn't really want such an an unsafe and low-level API, let's give
them something with the safety of git_config_get_string() instead.
This fix is similar to what the *_string() functions and others
acquired in[1] and [2]. Namely introducing and using a safer
"*_get_string_multi()" variant of the low-level "_*value_multi()"
function.
This fixes segfaults in code introduced in:
- d811c8e17c (versionsort: support reorder prerelease suffixes, 2015-02-26)
- c026557a37 (versioncmp: generalize version sort suffix reordering, 2016-12-08)
- a086f921a7 (submodule: decouple url and submodule interest, 2017-03-17)
- a6be5e6764 (log: add log.excludeDecoration config option, 2020-04-16)
- 92156291ca (log: add default decoration filter, 2022-08-05)
- 50a044f1e4 (gc: replace config subprocesses with API calls, 2022-09-27)
There are now two users ofthe low-level API:
- One in "builtin/for-each-repo.c", which we'll convert in a
subsequent commit.
- The "t/helper/test-config.c" code added in [3].
As seen in the preceding commit we need to give the
"t/helper/test-config.c" caller these "NULL" entries.
We could also alter the underlying git_configset_get_value_multi()
function to be "string safe", but doing so would leave no room for
other variants of "*_get_value_multi()" that coerce to other types.
Such coercion can't be built on the string version, since as we've
established "NULL" is a true value in the boolean context, but if we
coerced it to "" for use in a list of strings it'll be subsequently
coerced to "false" as a boolean.
The callback pattern being used here will make it easy to introduce
e.g. a "multi" variant which coerces its values to "bool", "int",
"path" etc.
1. 40ea4ed903 (Add config_error_nonbool() helper function,
2008-02-11)
2. 6c47d0e8f3 (config.c: guard config parser from value=NULL,
2008-02-11).
3. 4c715ebb96 (test-config: add tests for the config_set API,
2014-07-28)
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Have the "git_configset_get_value_multi()" function and its siblings
return an "int" and populate a "**dest" parameter like every other
git_configset_get_*()" in the API.
As we'll take advantage of in subsequent commits, this fixes a blind
spot in the API where it wasn't possible to tell whether a list was
empty from whether a config key existed. For now we don't make use of
those new return values, but faithfully convert existing API users.
Most of this is straightforward, commentary on cases that stand out:
- To ensure that we'll properly use the return values of this function
in the future we're using the "RESULT_MUST_BE_USED" macro introduced
in [1].
As git_die_config() now has to handle this return value let's have
it BUG() if it can't find the config entry. As tested for in a
preceding commit we can rely on getting the config list in
git_die_config().
- The loops after getting the "list" value in "builtin/gc.c" could
also make use of "unsorted_string_list_has_string()" instead of using
that loop, but let's leave that for now.
- In "versioncmp.c" we now use the return value of the functions,
instead of checking if the lists are still non-NULL.
1. 1e8697b5c4 (submodule--helper: check repo{_submodule,}_init()
return values, 2022-09-01),
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
With the change in the last commit to move several functions to
write-or-die.h, csum-file.h no longer needs to include cache.h.
However, removing that include forces several other C files, which
directly or indirectly dependend upon csum-file.h's inclusion of
cache.h, to now be more explicit about their dependencies.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Dozens of files made use of gettext functions, without explicitly
including gettext.h. This made it more difficult to find which files
could remove a dependence on cache.h. Make C files explicitly include
gettext.h if they are using it.
However, while compat/fsmonitor/fsm-ipc-darwin.c should also gain an
include of gettext.h, it was left out to avoid conflicting with an
in-flight topic.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
More work towards -Wunused.
* jk/unused-post-2.39-part2: (21 commits)
help: mark unused parameter in git_unknown_cmd_config()
run_processes_parallel: mark unused callback parameters
userformat_want_item(): mark unused parameter
for_each_commit_graft(): mark unused callback parameter
rewrite_parents(): mark unused callback parameter
fetch-pack: mark unused parameter in callback function
notes: mark unused callback parameters
prio-queue: mark unused parameters in comparison functions
for_each_object: mark unused callback parameters
list-objects: mark unused callback parameters
mark unused parameters in signal handlers
run-command: mark error routine parameters as unused
mark "pointless" data pointers in callbacks
ref-filter: mark unused callback parameters
http-backend: mark unused parameters in virtual functions
http-backend: mark argc/argv unused
object-name: mark unused parameters in disambiguate callbacks
serve: mark unused parameters in virtual functions
serve: use repository pointer to get config
ls-refs: drop config caching
...
Our graph-traversal functions take callbacks for showing commits and
objects, but not all callbacks need each parameter. Likewise for the
similar traverse_bitmap_commit_list(), which has a different interface
but serves the same purpose. And the include_check mechanism, which
passes along a void pointer which is not always used.
Mark the unused ones to to make -Wunused-parameter happy.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This allows us to replace includes of cache.h with includes of the much
smaller alloc.h in many places. It does mean that we also need to add
includes of alloc.h in a number of C files.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we find a midx bitmap, we do not bother checking for pack
bitmaps, since we can use only one. But since we will warn of unused
bitmaps via trace2, let's continue looking for pack bitmaps when
tracing is enabled.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
After opening a bitmap successfully, we try opening others only
because we want to report that other bitmap files are ignored in
the trace2 log. When trace2 is not enabled, we do not have to
do any of that.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In "open_midx_bitmap_1()" and "open_pack_bitmap_1()", when we find that
there are multiple bitmaps, we will only open the first one and then
leave warnings about the remaining pack information, the information
will contain the absolute path of the repository, for example in a
alternates usage scenario. So let's hide this kind of potentially
sensitive information in this commit.
Found-by: XingXin <moweng.xx@antgroup.com>
Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
When trying to open a pack bitmap, we call open_pack_bitmap_1() in a
loop, during which it tries to open up the pack index corresponding
with each available pack.
It's likely that we'll end up relying on objects in that pack later
in the process (in which case we're doing the work of opening the
pack index optimistically), but not guaranteed.
For instance, consider a repository with a large number of small
packs, and one large pack with a bitmap. If we see that bitmap pack
last in our loop which calls open_pack_bitmap_1(), the current code
will have opened *all* pack index files in the repository. If the
request can be served out of the bitmapped pack alone, then the time
spent opening these idx files was wasted.S
Since open_pack_bitmap_1() calls is_pack_valid() later on (which in
turns calls open_pack_index() itself), we can just drop the earlier
call altogether.
Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
The trace2 region around the call to lazy_bitmap_for_commit() in
bitmap_for_commit() was added in 28cd730680 (pack-bitmap: prepare to
read lookup table extension, 2022-08-14). While adding trace2 regions is
typically helpful for tracking performance, this method is called
possibly thousands of times as a commit walk explores commit history
looking for a matching bitmap. When trace2 output is enabled, this
region is emitted many times and performance is throttled by that
output.
For now, remove these regions entirely.
This is a critical path, and it would be valuable to measure that the
time spent in bitmap_for_commit() does not increase when using the
commit lookup table. The best way to do that would be to use a mechanism
that sums the time spent in a region and reports a single value at the
end of the process. This technique was introduced but not merged by [1]
so maybe this example presents some justification to revisit that
approach.
[1] https://lore.kernel.org/git/pull.1099.v2.git.1640720202.gitgitgadget@gmail.com/
To help with the 'git blame' output in this region, add a comment that
warns against adding a trace2 region. Delete a test from t5310 that used
that trace output to check that this lookup optimization was activated.
To create this kind of test again in the future, the stopwatch traces
mentioned earlier could be used as a signal that we activated this code
path.
Helpedy-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
