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>
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>
As we'll discuss in the subsequent commit these tests all
show *_get_value_multi() API users unable to handle there being a
value-less key in the config, which is represented with a "NULL" for
that entry in the "string" member of the returned "struct
string_list", causing a segfault.
These added tests exhaustively test for that issue, as we'll see in a
subsequent commit we'll need to change all of the API users
of *_get_value_multi(). These cases were discovered by triggering each
one individually, and then adding these tests.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@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>
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>
Earlier change teaches Git to write bitmap lookup table. But Git
does not know how to parse them.
Teach Git to parse the existing bitmap lookup table. The older
versions of Git are not affected by it. Those versions ignore the
lookup table.
Mentored-by: Taylor Blau <me@ttaylorr.com>
Co-Mentored-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
Signed-off-by: Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Teach Git to provide a way for users to enable/disable bitmap lookup
table extension by providing a config option named 'writeBitmapLookupTable'.
Default is false.
Also add test to verify writting of lookup table.
Mentored-by: Taylor Blau <me@ttaylorr.com>
Co-Mentored-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
Co-Authored-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When opening a MIDX/pack-bitmap, we call open_midx_bitmap_1() or
open_pack_bitmap_1() respectively in a loop over the set of MIDXs/packs.
By design, these functions are supposed to be called over every pack and
MIDX, since only one of them should have a valid bitmap.
Ordinarily we return '0' from these two functions in order to indicate
that we successfully loaded a bitmap To signal that we couldn't load a
bitmap corresponding to the MIDX/pack (either because one doesn't exist,
or because there was an error with loading it), we can return '-1'. In
either case, the callers each enumerate all MIDXs/packs to ensure that
at most one bitmap per-kind is present.
But when we fail to load a bitmap that does exist (for example, loading
a MIDX bitmap without finding a corresponding reverse index), we'll
return -1 but leave the 'midx' field non-NULL. So when we fallback to
loading a pack bitmap, we'll complain that the bitmap we're trying to
populate already is "opened", even though it isn't.
Rectify this by setting the '->pack' and '->midx' field back to NULL as
appropriate. Two tests are added: one to ensure that the MIDX-to-pack
bitmap fallback works, and another to ensure we still complain when
there are multiple pack bitmaps in a repository.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Broken &&-chains in the test scripts have been corrected.
* es/test-chain-lint:
t6000-t9999: detect and signal failure within loop
t5000-t5999: detect and signal failure within loop
t4000-t4999: detect and signal failure within loop
t0000-t3999: detect and signal failure within loop
tests: simplify by dropping unnecessary `for` loops
tests: apply modern idiom for exiting loop upon failure
tests: apply modern idiom for signaling test failure
tests: fix broken &&-chains in `{...}` groups
tests: fix broken &&-chains in `$(...)` command substitutions
tests: fix broken &&-chains in compound statements
tests: use test_write_lines() to generate line-oriented output
tests: simplify construction of large blocks of text
t9107: use shell parameter expansion to avoid breaking &&-chain
t6300: make `%(raw:size) --shell` test more robust
t5516: drop unnecessary subshell and command invocation
t4202: clarify intent by creating expected content less cleverly
t1020: avoid aborting entire test script when one test fails
t1010: fix unnoticed failure on Windows
t/lib-pager: use sane_unset() to avoid breaking &&-chain
Many tests that used to need GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
mechanism to force "git" to use 'master' as the default name for
the initial branch no longer need it; the use of the mechanism from
them have been removed.
* js/test-initial-branch-override-cleanup:
tests: set GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME only when needed
Failures within `for` and `while` loops can go unnoticed if not detected
and signaled manually since the loop itself does not abort when a
contained command fails, nor will a failure necessarily be detected when
the loop finishes since the loop returns the exit code of the last
command it ran on the final iteration, which may not be the command
which failed. Therefore, detect and signal failures manually within
loops using the idiom `|| return 1` (or `|| exit 1` within subshells).
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A couple of test scripts have actually been adapted to accommodate for a
configurable default branch name, but they still overrode it via the
`GIT_TEST_*` variable. Let's drop that override where possible.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous change modified GIT_TRACE2_EVENT_NESTING by default within
test-lib.sh. These custom assignments throughout the test suite are no
longer necessary.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Commit ddfe900612 (test-lib-functions: move function to lib-bitmap.sh,
2021-02-09) meant to include lib-bitmap.sh in t5310, but also includes
lib-bundle.sh. Yet we don't use any of its functions, nor have anything
to do with bundles. This is probably just a typo/copy-paste error, as
lib-bundle.sh was added (correctly) to other scripts in the same series.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Generating a MIDX bitmap confuses many of the tests in t5310, which
expect to control whether and how bitmaps are written. Since the
relevant MIDX-bitmap tests here are covered already in t5326, let's just
disable the flag for the whole t5310 script.
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>
We'll soon be adding a test script that will cover many of the same
bitmap concepts as t5310, but for MIDX bitmaps. Let's pull out as many
of the applicable tests as we can so we don't have to rewrite them.
There should be no functional change to t5310; we still run the same
operations in the same order.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When "git pack-objects" makes a literal copy of a part of existing
packfile using the reachability bitmaps, its update to the progress
meter was broken.
* jk/pack-objects-bitmap-progress-fix:
pack-objects: update "nr_seen" progress based on pack-reused count
When serving a clone or fetch with bitmaps, after deciding which objects
need to be sent our "pack reuse" mechanism kicks in: we try to send
more-or-less verbatim a bunch of objects from the beginning of the
bitmapped packfile without even adding them to the to_pack.objects
array.
After deciding which objects will be in the "reused" portion, we update
nr_result to account for those, and then trigger display_progress() to
show the user (who is undoubtedly dazzled that we managed to enumerate
so many objects so quickly).
But then something confusing happens: the "Enumerating objects" progress
meter jumps _backwards_, counting up from zero the number of objects we
actually add into to_pack.objects.
This worked correctly once upon a time, but was broken in 5af050437a
(pack-objects: show some progress when counting kept objects,
2018-04-15), when the latter half of that progress meter switched to
using a separate nr_seen counter, rather than nr_result. Nobody noticed
for two reasons:
- prior to the pack-reuse fixes from a14aebeac3 (Merge branch
'jk/packfile-reuse-cleanup', 2020-02-14), the reuse code almost
never kicked in anyway
- the output looks _kind of_ correct. The "backwards" moment is hard
to catch, because we overwrite the old progress number with the new
one, and the larger number is displayed only for a second. So unless
you look at that exact second, you just see the much smaller value,
counting up to the number of non-reused objects (though of course if
you catch it in stderr, or look at GIT_TRACE_PACKET from a server
with bitmaps, you can see both values).
This smaller output isn't wrong per se, but isn't counting what we ever
intended to. We should give the user the whole number of objects we
considered (which, as per 5af050437a's original purpose, is already
_not_ a count of what goes into to_pack.objects). The follow-on
"Counting objects" meter shows the actual number of objects we feed into
that array.
We can easily fix this by bumping (and showing) nr_seen for the
pack-reused objects. When the included test is run without this patch,
the second pack-objects invocation produces "Enumerating objects: 1" to
show the one loose object, even though the resulting pack has hundreds
of objects in it. With it, we jump to "Enumerating objects: 674" after
deciding on reuse, and then "675" when we add in the loose object.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When writing a new pack with a bitmap, it is sometimes convenient to
indicate some reference prefixes which should receive priority when
selecting which commits to receive bitmaps.
A truly motivated caller could accomplish this by setting
'pack.islandCore', (since all commits in the core island are similarly
marked as preferred) but this requires callers to opt into using delta
islands, which they may or may not want to do.
Introduce a new multi-valued configuration, 'pack.preferBitmapTips' to
allow callers to specify a list of reference prefixes. All references
which have a prefix contained in 'pack.preferBitmapTips' will mark their
tips as "preferred" in the same way as commits are marked as preferred
for selection by 'pack.islandCore'.
The choice of the verb "prefer" is intentional: marking the NEEDS_BITMAP
flag on an object does *not* guarantee that that object will receive a
bitmap. It merely guarantees that that commit will receive a bitmap over
any *other* commit in the same window by bitmap_writer_select_commits().
The test this patch adds reflects this quirk, too. It only tests that
a commit (which didn't receive bitmaps by default) is selected for
bitmaps after changing the value of 'pack.preferBitmapTips' to include
it. Other commits may lose their bitmaps as a byproduct of how the
selection process works (bitmap_writer_select_commits() ignores the
remainder of a window after seeing a commit with the NEEDS_BITMAP flag).
This configuration will aide in selecting important references for
multi-pack bitmaps, since they do not respect the same pack.islandCore
configuration. (They could, but doing so may be confusing, since it is
packs--not bitmaps--which are influenced by the delta-islands
configuration).
In a fork network repository (one which lists all forks of a given
repository as remotes), for example, it is useful to set
pack.preferBitmapTips to 'refs/remotes/<root>/heads' and
'refs/remotes/<root>/tags', where '<root>' is an opaque identifier
referring to the repository which is at the base of the fork chain.
Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Move a function added to test-lib-functions.sh in ea047a8eb4 (t5310:
factor out bitmap traversal comparison, 2020-02-14) into a new
lib-bitmap.sh.
The test-lib-functions.sh file should be for functions that are widely
used across the test suite, if something's only used by a few tests it
makes more sense to have it in a lib-*.sh file.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Prepare tests not to be affected by the name of the default branch
"git init" creates.
* js/default-branch-name-tests-final-stretch: (28 commits)
tests: drop prereq `PREPARE_FOR_MAIN_BRANCH` where no longer needed
t99*: adjust the references to the default branch name "main"
tests(git-p4): transition to the default branch name `main`
t9[5-7]*: adjust the references to the default branch name "main"
t9[0-4]*: adjust the references to the default branch name "main"
t8*: adjust the references to the default branch name "main"
t7[5-9]*: adjust the references to the default branch name "main"
t7[0-4]*: adjust the references to the default branch name "main"
t6[4-9]*: adjust the references to the default branch name "main"
t64*: preemptively adjust alignment to prepare for `master` -> `main`
t6[0-3]*: adjust the references to the default branch name "main"
t5[6-9]*: adjust the references to the default branch name "main"
t55[4-9]*: adjust the references to the default branch name "main"
t55[23]*: adjust the references to the default branch name "main"
t551*: adjust the references to the default branch name "main"
t550*: adjust the references to the default branch name "main"
t5503: prepare aligned comment for replacing `master` with `main`
t5[0-4]*: adjust the references to the default branch name "main"
t5323: prepare centered comment for `master` -> `main`
t4*: adjust the references to the default branch name "main"
...
Various improvements to the codepath that writes out pack bitmaps.
* tb/pack-bitmap: (24 commits)
pack-bitmap-write: better reuse bitmaps
pack-bitmap-write: relax unique revwalk condition
pack-bitmap-write: use existing bitmaps
pack-bitmap: factor out 'add_commit_to_bitmap()'
pack-bitmap: factor out 'bitmap_for_commit()'
pack-bitmap-write: ignore BITMAP_FLAG_REUSE
pack-bitmap-write: build fewer intermediate bitmaps
pack-bitmap.c: check reads more aggressively when loading
pack-bitmap-write: rename children to reverse_edges
t5310: add branch-based checks
commit: implement commit_list_contains()
bitmap: implement bitmap_is_subset()
pack-bitmap-write: fill bitmap with commit history
pack-bitmap-write: pass ownership of intermediate bitmaps
pack-bitmap-write: reimplement bitmap writing
ewah: add bitmap_dup() function
ewah: implement bitmap_or()
ewah: make bitmap growth less aggressive
ewah: factor out bitmap growth
rev-list: die when --test-bitmap detects a mismatch
...
The previous commits improved the bitmap computation process for very
long, linear histories with many refs by removing quadratic growth in
how many objects were walked. The strategy of computing "intermediate
commits" using bitmasks for which refs can reach those commits
partitioned the poset of reachable objects so each part could be walked
exactly once. This was effective for linear histories.
However, there was a (significant) drawback: wide histories with many
refs had an explosion of memory costs to compute the commit bitmasks
during the exploration that discovers these intermediate commits. Since
these wide histories are unlikely to repeat walking objects, the benefit
of walking objects multiple times was not expensive before. But now, the
commit walk *before computing bitmaps* is incredibly expensive.
In an effort to discover a happy medium, this change reduces the walk
for intermediate commits to only the first-parent history. This focuses
the walk on how the histories converge, which still has significant
reduction in repeat object walks. It is still possible to create
quadratic behavior in this version, but it is probably less likely in
realistic data shapes.
Here is some data taken on a fresh clone of the kernel:
| runtime (sec) | peak heap (GB) |
| | |
| from | with | from | with |
| scratch | existing | scratch | existing |
-----------+---------+----------+---------+-----------
original | 64.044 | 83.241 | 2.088 | 2.194 |
last patch | 45.049 | 37.624 | 2.267 | 2.334 |
this patch | 88.478 | 53.218 | 2.157 | 2.224 |
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bitmap_writer_build() method calls bitmap_builder_init() to
construct a list of commits reachable from the selected commits along
with a "reverse graph". This reverse graph has edges pointing from a
commit to other commits that can reach that commit. After computing a
reachability bitmap for a commit, the values in that bitmap are then
copied to the reachability bitmaps across the edges in the reverse
graph.
We can now relax the role of the reverse graph to greatly reduce the
number of intermediate reachability bitmaps we compute during this
reverse walk. The end result is that we walk objects the same number of
times as before when constructing the reachability bitmaps, but we also
spend much less time copying bits between bitmaps and have much lower
memory pressure in the process.
The core idea is to select a set of "important" commits based on
interactions among the sets of commits reachable from each selected commit.
The first technical concept is to create a new 'commit_mask' member in the
bb_commit struct. Note that the selected commits are provided in an
ordered array. The first thing to do is to mark the ith bit in the
commit_mask for the ith selected commit. As we walk the commit-graph, we
copy the bits in a commit's commit_mask to its parents. At the end of
the walk, the ith bit in the commit_mask for a commit C stores a boolean
representing "The ith selected commit can reach C."
As we walk, we will discover non-selected commits that are important. We
will get into this later, but those important commits must also receive
bit positions, growing the width of the bitmasks as we walk. At the true
end of the walk, the ith bit means "the ith _important_ commit can reach
C."
MAXIMAL COMMITS
---------------
We use a new 'maximal' bit in the bb_commit struct to represent whether
a commit is important or not. The term "maximal" comes from the
partially-ordered set of commits in the commit-graph where C >= P if P
is a parent of C, and then extending the relationship transitively.
Instead of taking the maximal commits across the entire commit-graph, we
instead focus on selecting each commit that is maximal among commits
with the same bits on in their commit_mask. This definition is
important, so let's consider an example.
Suppose we have three selected commits A, B, and C. These are assigned
bitmasks 100, 010, and 001 to start. Each of these can be marked as
maximal immediately because they each will be the uniquely maximal
commit that contains their own bit. Keep in mind that that these commits
may have different bitmasks after the walk; for example, if B can reach
C but A cannot, then the final bitmask for C is 011. Even in these
cases, C would still be a maximal commit among all commits with the
third bit on in their masks.
Now define sets X, Y, and Z to be the sets of commits reachable from A,
B, and C, respectively. The intersections of these sets correspond to
different bitmasks:
* 100: X - (Y union Z)
* 010: Y - (X union Z)
* 001: Z - (X union Y)
* 110: (X intersect Y) - Z
* 101: (X intersect Z) - Y
* 011: (Y intersect Z) - X
* 111: X intersect Y intersect Z
This can be visualized with the following Hasse diagram:
100 010 001
| \ / \ / |
| \/ \/ |
| /\ /\ |
| / \ / \ |
110 101 011
\___ | ___/
\ | /
111
Some of these bitmasks may not be represented, depending on the topology
of the commit-graph. In fact, we are counting on it, since the number of
possible bitmasks is exponential in the number of selected commits, but
is also limited by the total number of commits. In practice, very few
bitmasks are possible because most commits converge on a common "trunk"
in the commit history.
With this three-bit example, we wish to find commits that are maximal
for each bitmask. How can we identify this as we are walking?
As we walk, we visit a commit C. Since we are walking the commits in
topo-order, we know that C is visited after all of its children are
visited. Thus, when we get C from the revision walk we inspect the
'maximal' property of its bb_data and use that to determine if C is truly
important. Its commit_mask is also nearly final. If C is not one of the
originally-selected commits, then assign a bit position to C (by
incrementing num_maximal) and set that bit on in commit_mask. See
"MULTIPLE MAXIMAL COMMITS" below for more detail on this.
Now that the commit C is known to be maximal or not, consider each
parent P of C. Compute two new values:
* c_not_p : true if and only if the commit_mask for C contains a bit
that is not contained in the commit_mask for P.
* p_not_c : true if and only if the commit_mask for P contains a bit
that is not contained in the commit_mask for P.
If c_not_p is false, then P already has all of the bits that C would
provide to its commit_mask. In this case, move on to other parents as C
has nothing to contribute to P's state that was not already provided by
other children of P.
We continue with the case that c_not_p is true. This means there are
bits in C's commit_mask to copy to P's commit_mask, so use bitmap_or()
to add those bits.
If p_not_c is also true, then set the maximal bit for P to one. This means
that if no other commit has P as a parent, then P is definitely maximal.
This is because no child had the same bitmask. It is important to think
about the maximal bit for P at this point as a temporary state: "P is
maximal based on current information."
In contrast, if p_not_c is false, then set the maximal bit for P to
zero. Further, clear all reverse_edges for P since any edges that were
previously assigned to P are no longer important. P will gain all
reverse edges based on C.
The final thing we need to do is to update the reverse edges for P.
These reverse edges respresent "which closest maximal commits
contributed bits to my commit_mask?" Since C contributed bits to P's
commit_mask in this case, C must add to the reverse edges of P.
If C is maximal, then C is a 'closest' maximal commit that contributed
bits to P. Add C to P's reverse_edges list.
Otherwise, C has a list of maximal commits that contributed bits to its
bitmask (and this list is exactly one element). Add all of these items
to P's reverse_edges list. Be careful to ignore duplicates here.
After inspecting all parents P for a commit C, we can clear the
commit_mask for C. This reduces the memory load to be limited to the
"width" of the commit graph.
Consider our ABC/XYZ example from earlier and let's inspect the state of
the commits for an interesting bitmask, say 011. Suppose that D is the
only maximal commit with this bitmask (in the first three bits). All
other commits with bitmask 011 have D as the only entry in their
reverse_edges list. D's reverse_edges list contains B and C.
COMPUTING REACHABILITY BITMAPS
------------------------------
Now that we have our definition, let's zoom out and consider what
happens with our new reverse graph when computing reachability bitmaps.
We walk the reverse graph in reverse-topo-order, so we visit commits
with largest commit_masks first. After we compute the reachability
bitmap for a commit C, we push the bits in that bitmap to each commit D
in the reverse edge list for C. Then, when we finally visit D we already
have the bits for everything reachable from maximal commits that D can
reach and we only need to walk the objects in the set-difference.
In our ABC/XYZ example, when we finally walk for the commit A we only
need to walk commits with bitmask equal to A's bitmask. If that bitmask
is 100, then we are only walking commits in X - (Y union Z) because the
bitmap already contains the bits for objects reachable from (X intersect
Y) union (X intersect Z) (i.e. the bits from the reachability bitmaps
for the maximal commits with bitmasks 110 and 101).
The behavior is intended to walk each commit (and the trees that commit
introduces) at most once while allocating and copying fewer reachability
bitmaps. There is one caveat: what happens when there are multiple
maximal commits with the same bitmask, with respect to the initial set
of selected commits?
MULTIPLE MAXIMAL COMMITS
------------------------
Earlier, we mentioned that when we discover a new maximal commit, we
assign a new bit position to that commit and set that bit position to
one for that commit. This is absolutely important for interesting
commit-graphs such as git/git and torvalds/linux. The reason is due to
the existence of "butterflies" in the commit-graph partial order.
Here is an example of four commits forming a butterfly:
I J
|\ /|
| \/ |
| /\ |
|/ \|
M N
\ /
|/
Q
Here, I and J both have parents M and N. In general, these do not need
to be exact parent relationships, but reachability relationships. The
most important part is that M and N cannot reach each other, so they are
independent in the partial order. If I had commit_mask 10 and J had
commit_mask 01, then M and N would both be assigned commit_mask 11 and
be maximal commits with the bitmask 11. Then, what happens when M and N
can both reach a commit Q? If Q is also assigned the bitmask 11, then it
is not maximal but is reachable from both M and N.
While this is not necessarily a deal-breaker for our abstract definition
of finding maximal commits according to a given bitmask, we have a few
issues that can come up in our larger picture of constructing
reachability bitmaps.
In particular, if we do not also consider Q to be a "maximal" commit,
then we will walk commits reachable from Q twice: once when computing
the reachability bitmap for M and another time when computing the
reachability bitmap for N. This becomes much worse if the topology
continues this pattern with multiple butterflies.
The solution has already been mentioned: each of M and N are assigned
their own bits to the bitmask and hence they become uniquely maximal for
their bitmasks. Finally, Q also becomes maximal and thus we do not need
to walk its commits multiple times. The final bitmasks for these commits
are as follows:
I:10 J:01
|\ /|
| \ _____/ |
| /\____ |
|/ \ |
M:111 N:1101
\ /
Q:1111
Further, Q's reverse edge list is { M, N }, while M and N both have
reverse edge list { I, J }.
PERFORMANCE MEASUREMENTS
------------------------
Now that we've spent a LOT of time on the theory of this algorithm,
let's show that this is actually worth all that effort.
To test the performance, use GIT_TRACE2_PERF=1 when running
'git repack -abd' in a repository with no existing reachability bitmaps.
This avoids any issues with keeping existing bitmaps to skew the
numbers.
Inspect the "building_bitmaps_total" region in the trace2 output to
focus on the portion of work that is affected by this change. Here are
the performance comparisons for a few repositories. The timings are for
the following versions of Git: "multi" is the timing from before any
reverse graph is constructed, where we might perform multiple
traversals. "reverse" is for the previous change where the reverse graph
has every reachable commit. Finally "maximal" is the version introduced
here where the reverse graph only contains the maximal commits.
Repository: git/git
multi: 2.628 sec
reverse: 2.344 sec
maximal: 2.047 sec
Repository: torvalds/linux
multi: 64.7 sec
reverse: 205.3 sec
maximal: 44.7 sec
So in all cases we've not only recovered any time lost to switching to
the reverse-edge algorithm, but we come out ahead of "multi" in all
cases. Likewise, peak heap has gone back to something reasonable:
Repository: torvalds/linux
multi: 2.087 GB
reverse: 3.141 GB
maximal: 2.288 GB
While I do not have access to full fork networks on GitHub, Peff has run
this algorithm on the chromium/chromium fork network and reported a
change from 3 hours to ~233 seconds. That network is particularly
beneficial for this approach because it has a long, linear history along
with many tags. The "multi" approach was obviously quadratic and the new
approach is linear.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The current rev-list tests that check the bitmap data only work on HEAD
instead of multiple branches. Expand the test cases to handle both
'master' and 'other' branches.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We truncate the .bitmap file to 512 bytes and expect to run into
problems reading an individual ewah file. But this length is somewhat
arbitrary, and just happened to work when the test was added in
9d2e330b17 (ewah_read_mmap: bounds-check mmap reads, 2018-06-14).
An upcoming commit will change the size of the history we create in the
test repo, which will cause this test to fail. We can future-proof it a
bit more by reducing the size of the truncated bitmap file.
Signed-off-by: Jeff King <peff@peff.net>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A .bitmap file may have a "name hash cache" extension, which puts a
sequence of uint32_t values (one per object) at the end of the file.
When we see a flag indicating this extension, we blindly subtract the
appropriate number of bytes from our available length. However, if the
.bitmap file is too short, we'll underflow our length variable and wrap
around, thinking we have a very large length. This can lead to reading
out-of-bounds bytes while loading individual ewah bitmaps.
We can fix this by checking the number of available bytes when we parse
the header. The existing "truncated bitmap" test is now split into two
tests: one where we don't have this extension at all (and hence actually
do try to read a truncated ewah bitmap) and one where we realize
up-front that we can't even fit in the cache structure. We'll check
stderr in each case to make sure we hit the error we're expecting.
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>
In addition to the manual adjustment to let the `linux-gcc` CI job run
the test suite with `master` and then with `main`, this patch makes sure
that GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME is set in all test scripts
that currently rely on the initial branch name being `master by default.
To determine which test scripts to mark up, the first step was to
force-set the default branch name to `master` in
- all test scripts that contain the keyword `master`,
- t4211, which expects `t/t4211/history.export` with a hard-coded ref to
initialize the default branch,
- t5560 because it sources `t/t556x_common` which uses `master`,
- t8002 and t8012 because both source `t/annotate-tests.sh` which also
uses `master`)
This trick was performed by this command:
$ sed -i '/^ *\. \.\/\(test-lib\|lib-\(bash\|cvs\|git-svn\)\|gitweb-lib\)\.sh$/i\
GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master\
export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME\
' $(git grep -l master t/t[0-9]*.sh) \
t/t4211*.sh t/t5560*.sh t/t8002*.sh t/t8012*.sh
After that, careful, manual inspection revealed that some of the test
scripts containing the needle `master` do not actually rely on a
specific default branch name: either they mention `master` only in a
comment, or they initialize that branch specificially, or they do not
actually refer to the current default branch. Therefore, the
aforementioned modification was undone in those test scripts thusly:
$ git checkout HEAD -- \
t/t0027-auto-crlf.sh t/t0060-path-utils.sh \
t/t1011-read-tree-sparse-checkout.sh \
t/t1305-config-include.sh t/t1309-early-config.sh \
t/t1402-check-ref-format.sh t/t1450-fsck.sh \
t/t2024-checkout-dwim.sh \
t/t2106-update-index-assume-unchanged.sh \
t/t3040-subprojects-basic.sh t/t3301-notes.sh \
t/t3308-notes-merge.sh t/t3423-rebase-reword.sh \
t/t3436-rebase-more-options.sh \
t/t4015-diff-whitespace.sh t/t4257-am-interactive.sh \
t/t5323-pack-redundant.sh t/t5401-update-hooks.sh \
t/t5511-refspec.sh t/t5526-fetch-submodules.sh \
t/t5529-push-errors.sh t/t5530-upload-pack-error.sh \
t/t5548-push-porcelain.sh \
t/t5552-skipping-fetch-negotiator.sh \
t/t5572-pull-submodule.sh t/t5608-clone-2gb.sh \
t/t5614-clone-submodules-shallow.sh \
t/t7508-status.sh t/t7606-merge-custom.sh \
t/t9302-fast-import-unpack-limit.sh
We excluded one set of test scripts in these commands, though: the range
of `git p4` tests. The reason? `git p4` stores the (foreign) remote
branch in the branch called `p4/master`, which is obviously not the
default branch. Manual analysis revealed that only five of these tests
actually require a specific default branch name to pass; They were
modified thusly:
$ sed -i '/^ *\. \.\/lib-git-p4\.sh$/i\
GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master\
export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME\
' t/t980[0167]*.sh t/t9811*.sh
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 't5310-pack-bitmaps.sh' two tests make sure that our pack bitmaps
are compatible with JGit's bitmaps. Alas, not even the most recent
JGit version (5.9.0.202009080501-r) supports SHA256 yet, so when this
test script is run with GIT_TEST_DEFAULT_HASH=sha256 on a setup with
JGit installed in PATH, then these two tests fail.
Protect these two tests with the SHA1 prereq in order to skip them
when testing with SHA256.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Just as rev-list recently learned to combine filters and bitmaps, let's
do the same for pack-objects. The infrastructure is all there; we just
need to pass along our filter options, and the pack-bitmap code will
decide to use bitmaps or not.
This unsurprisingly makes things faster for partial clones of large
repositories (here we're cloning linux.git):
Test HEAD^ HEAD
------------------------------------------------------------------------------
5310.11: simulated partial clone 38.94(37.28+5.87) 11.06(11.27+4.07) -71.6%
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Ever since we added reachability bitmap support, we've been able to use
it with rev-list to get the full list of objects, like:
git rev-list --objects --use-bitmap-index --all
But you can't do so without --objects, since we weren't ready to just
show the commits. However, the internals of the bitmap code are mostly
ready for this: they avoid opening up trees when walking to fill in the
bitmaps. We just need to actually pass in the rev_info to
traverse_bitmap_commit_list() so it knows which types to bother
triggering our callback for.
For completeness, the perf test now covers both the existing --objects
case, as well as the new commits-only behavior (the objects one got way
faster when we introduced bitmaps, but obviously isn't improved now).
Here are numbers for linux.git:
Test HEAD^ HEAD
------------------------------------------------------------------------
5310.7: rev-list (commits) 8.29(8.10+0.19) 1.76(1.72+0.04) -78.8%
5310.8: rev-list (objects) 8.06(7.94+0.12) 8.14(7.94+0.13) +1.0%
That run was cheating a little, as I didn't have any commit-graph in the
repository, and we'd built it by default these days when running git-gc.
Here are numbers with a commit-graph:
Test HEAD^ HEAD
------------------------------------------------------------------------
5310.7: rev-list (commits) 0.70(0.58+0.12) 0.51(0.46+0.04) -27.1%
5310.8: rev-list (objects) 6.20(6.09+0.10) 6.27(6.16+0.11) +1.1%
Still an improvement, but a lot less impressive.
We could have the perf script remove any commit-graph to show the
out-sized effect, but it probably makes sense to leave it in what would
be a more typical setup.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We check the results of "rev-list --use-bitmap-index" by comparing it to
the same traversal without the bitmap option. However, this is a little
tricky to do because of some output differences (see the included
comment for details). Let's pull this out into a helper function, since
we'll be adding some similar tests.
While we're at it, let's also try to confirm that the bitmap output did
indeed use bitmaps. Since the code internally falls back to the
non-bitmap path in some cases, the tests are at risk of becoming trivial
noops.
This is a bit fragile, as not all outputs will differ (e.g., looking at
only the commits from a fully-bitmapped pack will end up exactly the
same as the normal traversal order, since it also matches the pack
order). So we'll provide an escape hatch by which tests can disable this
check (which should only be used after manually confirming that bitmaps
kicked in).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The prior commit taught "--count --objects" to work without bitmaps. We
should be able to get the same answer much more quickly with bitmaps.
Note that we punt on the max_count case here. This perhaps _could_ be
made to work if we find all of the boundary commits and treat them as
UNINTERESTING, subtracting them (and their reachable objects) from the
set we return. That implies an actual commit traversal, but we'd still
be faster due to avoiding opening up any trees. Given the complexity and
the fact that anyone is unlikely to want this, it makes sense to just
fall back to the non-bitmap case for now.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bitmap index we compute in t5310 has only 20 commits in it. This
gives poor coverage of bitmap_writer_select_commits(), which simply
writes a bitmap for everything when there are fewer than 100 commits.
Let's bump the number of commits in the test to cover the more complex
code paths (this does drop coverage of the individual lines of the
trivial path, but the complex path does everything it does and more).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Some tests need to create a string of commits. Doing this with
test_commit is very heavy-weight, as it needs at least one process per
commit (and in fact, uses several).
For bulk creation, we can do much better by using fast-import, but it's
often a pain to generate the input. Let's provide a helper to do so.
We'll use t5310 as a guinea pig, as it has three 10-commit loops. Here
are hyperfine results before and after:
[before]
Benchmark #1: ./t5310-pack-bitmaps.sh --root=/var/ram/git-tests
Time (mean ± σ): 2.846 s ± 0.305 s [User: 3.042 s, System: 0.919 s]
Range (min … max): 2.250 s … 3.210 s 10 runs
[after]
Benchmark #1: ./t5310-pack-bitmaps.sh --root=/var/ram/git-tests
Time (mean ± σ): 2.210 s ± 0.174 s [User: 2.570 s, System: 0.604 s]
Range (min … max): 1.999 s … 2.590 s 10 runs
So we're over 20% faster, while making the callers slightly shorter. We
added a lot more lines in test-lib-function.sh, of course, and the
helper is way more featureful than we need here. But my hope is that it
will be flexible enough to use in more places.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Enabling pack.writebitmaphashcache should always be a performance win.
It costs only 4 bytes per object on disk, and the timings in ae4f07fbcc
(pack-bitmap: implement optional name_hash cache, 2013-12-21) show it
improving fetch and partial-bitmap clone times by 40-50%.
The only reason we didn't enable it by default at the time is that early
versions of JGit's bitmap reader complained about the presence of
optional header bits it didn't understand. But that was changed in
JGit's d2fa3987a (Use bitcheck to check for presence of OPT_FULL option,
2013-10-30), which made it into JGit v3.5.0 in late 2014.
So let's turn this option on by default. It's backwards-compatible with
all versions of Git, and if you are also using JGit on the same
repository, you'd only run into problems using a version that's almost 5
years old.
We'll drop the manual setting from all of our test scripts, including
perf tests. This isn't strictly necessary, but it has two advantages:
1. If the hash-cache ever stops being enabled by default, our perf
regression tests will notice.
2. We can use the modified perf tests to show off the behavior of an
otherwise unconfigured repo, as shown below.
These are the results of a few of a perf tests against linux.git that
showed interesting results. You can see the expected speedup in 5310.4,
which was noted in ae4f07fbcc. Curiously, 5310.8 did not improve (and
actually got slower), despite seeing the opposite in ae4f07fbcc.
I don't have an explanation for that.
The tests from p5311 did not exist back then, but do show improvements
(a smaller pack due to better deltas, which we found in less time).
Test HEAD^ HEAD
-------------------------------------------------------------------------------------
5310.4: simulated fetch 7.39(22.70+0.25) 5.64(11.43+0.22) -23.7%
5310.8: clone (partial bitmap) 18.45(24.83+1.19) 19.94(28.40+1.36) +8.1%
5311.31: server (128 days) 0.41(1.13+0.05) 0.34(0.72+0.02) -17.1%
5311.32: size (128 days) 7.4M 7.0M -4.8%
5311.33: client (128 days) 1.33(1.49+0.06) 1.29(1.37+0.12) -3.0%
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We use "jgit gc" to generate a pack bitmap file, and then make sure our
implementation can read it. To prepare the repo before running jgit, we
try to "rm -f" any existing bitmap files. But we got the path wrong;
we're in a bare repo, so looking in ".git/" finds nothing. Our "rm"
doesn't complain because of the "-f", and when we run "rev-list" there
are two bitmap files (ours and jgit's).
Our reader implementation will ignore one of the bitmap files, but it's
likely non-deterministic which one we will use. We'd prefer the one with
the more recent timestamp (just because of the way the packed_git list
is sorted), but in most test runs they'd have identical timestamps.
So this was probably actually testing something useful about 50% of the
time, and other half just testing that we could read our own bitmaps
(which is covered elsewhere).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The multi-pack-index feature is tested in isolation by
t5319-multi-pack-index.sh, but there are many more interesting
scenarios in the test suite surrounding pack-file data shapes
and interactions. Since the multi-pack-index is an optional
data structure, it does not make sense to include it by default
in those tests.
Instead, add a new GIT_TEST_MULTI_PACK_INDEX environment variable
that enables core.multiPackIndex and writes a multi-pack-index
after each 'git repack' command. This adds extra test coverage
when needed.
There are a few spots in the test suite that need to react to this
change:
* t5319-multi-pack-index.sh: there is a test that checks that
'git repack' deletes the multi-pack-index. Disable the environment
variable to ensure this still happens.
* t5310-pack-bitmaps.sh: One test moves a pack-file from the object
directory to an alternate. This breaks the multi-pack-index, so
delete the multi-pack-index at this point, if it exists.
* t9300-fast-import.sh: One test verifies the number of files in
the .git/objects/pack directory is exactly 8. Exclude the
multi-pack-index from this count so it is still 8 in all cases.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Hotfix of the base topic.
* jk/pack-objects-with-bitmap-fix:
pack-bitmap: drop "loaded" flag
traverse_bitmap_commit_list(): don't free result
t5310: test delta reuse with bitmaps
bitmap_has_sha1_in_uninteresting(): drop BUG check
Commit 6a1e32d532 (pack-objects: reuse on-disk deltas for
thin "have" objects, 2018-08-21) taught pack-objects a new
optimization trick. Since this wasn't meant to change
user-visible behavior, but only produce smaller packs more
quickly, testing focused on t/perf/p5311.
However, since people don't run perf tests very often, we
should make sure that the feature is exercised in the
regular test suite. This patch does so.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The "head -c BYTES" option is non-portable (not in POSIX[1]). Change
such invocations to use the test_copy_bytes wrapper added in
48860819e8 ("t9300: factor out portable "head -c" replacement",
2016-06-30).
This fixes a test added in 9d2e330b17 ("ewah_read_mmap: bounds-check
mmap reads", 2018-06-14), which has been breaking
t5310-pack-bitmaps.sh on OpenBSD since 2.18.0. The OpenBSD ports
already have a similar workaround after their upgrade to 2.18.0[2].
I have not tested this on IRIX, but according to 4de0bbd898 ("t9300:
use perl "head -c" clone in place of "dd bs=1 count=16000" kluge",
2010-12-13) this invocation would have broken things there too.
Also, change a valgrind-specific codepath in test-lib.sh to use this
wrapper. Given where valgrind runs I don't think this would ever
become a portability issue in practice, but it's easier to just use
the wrapper than introduce some exception for the "make test-lint"
check being added here.
1. http://pubs.opengroup.org/onlinepubs/9699919799/utilities/head.html
2. 08d5d82eae (diff-f7d3c4fabeed1691620d608f1534f5e5)
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The test 'pack-objects to file can use bitmap' added in 645c432d61
(pack-objects: use reachability bitmap index when generating
non-stdout pack, 2016-09-10) is silently buggy and doesn't check what
it's supposed to.
In 't5310-pack-bitmaps.sh', the 'list_packed_objects' helper function
does what its name implies by running:
git show-index <"$1" | cut -d' ' -f2
The test in question invokes this function like this:
list_packed_objects <packa-$packasha1.idx >packa.objects &&
list_packed_objects <packb-$packbsha1.idx >packb.objects &&
test_cmp packa.objects packb.objects
Note how these two callsites don't specify the name of the pack index
file as the function's parameter, but redirect the function's standard
input from it. This triggers an error message from the shell, as it
has no filename to redirect from in the function, but this error is
ignored, because it happens upstream of a pipe. Consequently, both
invocations produce empty 'pack{a,b}.objects' files, and the
subsequent 'test_cmp' happily finds those two empty files identical.
Fix these two 'list_packed_objects' invocations by specifying the pack
index files as parameters. Furthermore, eliminate the pipe in that
function by replacing it with an &&-chained pair of commands using an
intermediate file, so a failure of 'git show-index' or the shell
redirection will fail the test.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Change various tests that use an idiom of the form:
>expect &&
test_cmp expect actual
To instead use:
test_must_be_empty actual
The test_must_be_empty() wrapper was introduced in ca8d148daf ("test:
test_must_be_empty helper", 2013-06-09). Many of these tests have been
added after that time. This was mostly found with, and manually pruned
from:
git grep '^\s+>.*expect.* &&$' t
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The code to read compressed bitmap was not careful to avoid reading
past the end of the file, which has been corrected.
* jk/ewah-bounds-check:
ewah: adjust callers of ewah_read_mmap()
ewah_read_mmap: bounds-check mmap reads
The on-disk ewah format tells us how big the ewah data is,
and we blindly read that much from the buffer without
considering whether the mmap'd data is long enough, which
can lead to out-of-bound reads.
Let's make sure we have data available before reading it,
both for the ewah header/footer as well as for the bit data
itself. In particular:
- keep our ptr/len pair in sync as we move through the
buffer, and check it before each read
- check the size for integer overflow (this should be
impossible on 64-bit, as the size is given as a 32-bit
count of 8-byte words, but is possible on a 32-bit
system)
- return the number of bytes read as an ssize_t instead of
an int, again to prevent integer overflow
- compute the return value using a pointer difference;
this should yield the same result as the existing code,
but makes it more obvious that we got our computations
right
The included test is far from comprehensive, as it just
picks a static point at which to truncate the generated
bitmap. But in practice this will hit in the middle of an
ewah and make sure we're at least exercising this code.
Reported-by: Luat Nguyen <root@l4w.io>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The two JGit tests 'we can read jgit bitmaps' and 'jgit can read our
bitmaps' in 't5310-pack-bitmaps.sh' fail when run with
GIT_TEST_SPLIT_INDEX=YesPlease. Both tests create a clone of the test
repository to check bitmap interoperability with JGit. With split
indexes enabled the index in the clone repositories contains the
'link' extension, which JGit doesn't support and, consequently, an
exception aborts it:
<...>
org.eclipse.jgit.api.errors.JGitInternalException: DIRC extension 'link' not supported by this version.
at org.eclipse.jgit.dircache.DirCache.readFrom(DirCache.java:562)
<...>
Since testing bitmaps doesn't need a worktree in the first place,
let's just create bare clones for the two JGit tests, so the cloned
won't have an index, and these two tests can be executed even with
split index enabled.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
