git/t/t5310-pack-bitmaps.sh

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#!/bin/sh
test_description='exercise basic bitmap functionality'
tests: mark tests relying on the current default for `init.defaultBranch` 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$/i\ GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master\ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME\ ' t/t980[0167]*.sh t/t9811*.sh Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-11-18 23:44:19 +00:00
. ./test-lib.sh
. "$TEST_DIRECTORY"/lib-bitmap.sh
# t5310 deals only with single-pack bitmaps, so don't write MIDX bitmaps in
# their place.
GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP=0
pack-bitmap.c: use commit boundary during bitmap traversal 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>
2023-05-08 17:38:12 +00:00
# Likewise, allow individual tests to control whether or not they use
# the boundary-based traversal.
sane_unset GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL
add `ignore_missing_links` mode to revwalk When pack-objects is computing the reachability bitmap to serve a fetch request, it can erroneously die() if some of the UNINTERESTING objects are not present. Upload-pack throws away HAVE lines from the client for objects we do not have, but we may have a tip object without all of its ancestors (e.g., if the tip is no longer reachable and was new enough to survive a `git prune`, but some of its reachable objects did get pruned). In the non-bitmap case, we do a revision walk with the HAVE objects marked as UNINTERESTING. The revision walker explicitly ignores errors in accessing UNINTERESTING commits to handle this case (and we do not bother looking at UNINTERESTING trees or blobs at all). When we have bitmaps, however, the process is quite different. The bitmap index for a pack-objects run is calculated in two separate steps: First, we perform an extensive walk from all the HAVEs to find the full set of objects reachable from them. This walk is usually optimized away because we are expected to hit an object with a bitmap during the traversal, which allows us to terminate early. Secondly, we perform an extensive walk from all the WANTs, which usually also terminates early because we hit a commit with an existing bitmap. Once we have the resulting bitmaps from the two walks, we AND-NOT them together to obtain the resulting set of objects we need to pack. When we are walking the HAVE objects, the revision walker does not know that we are walking it only to mark the results as uninteresting. We strip out the UNINTERESTING flag, because those objects _are_ interesting to us during the first walk. We want to keep going to get a complete set of reachable objects if we can. We need some way to tell the revision walker that it's OK to silently truncate the HAVE walk, just like it does for the UNINTERESTING case. This patch introduces a new `ignore_missing_links` flag to the `rev_info` struct, which we set only for the HAVE walk. It also adds tests to cover UNINTERESTING objects missing from several positions: a missing blob, a missing tree, and a missing parent commit. The missing blob already worked (as we do not care about its contents at all), but the other two cases caused us to die(). Note that there are a few cases we do not need to test: 1. We do not need to test a missing tree, with the blob still present. Without the tree that refers to it, we would not know that the blob is relevant to our walk. 2. We do not need to test a tip commit that is missing. Upload-pack omits these for us (and in fact, we complain even in the non-bitmap case if it fails to do so). Reported-by: Siddharth Agarwal <sid0@fb.com> Signed-off-by: Vicent Marti <tanoku@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2014-03-28 10:00:43 +00:00
objpath () {
echo ".git/objects/$(echo "$1" | sed -e 's|\(..\)|\1/|')"
}
pack-objects: respect --local/--honor-pack-keep/--incremental when bitmap is in use Since 6b8fda2d (pack-objects: use bitmaps when packing objects) there are two codepaths in pack-objects: with & without using bitmap reachability index. However add_object_entry_from_bitmap(), despite its non-bitmapped counterpart add_object_entry(), in no way does check for whether --local or --honor-pack-keep or --incremental should be respected. In non-bitmapped codepath this is handled in want_object_in_pack(), but bitmapped codepath has simply no such checking at all. The bitmapped codepath however was allowing to pass in all those options and with bitmap indices still being used under such conditions - potentially giving wrong output (e.g. including objects from non-local or .keep'ed pack). We can easily fix this by noting the following: when an object comes to add_object_entry_from_bitmap() it can come for two reasons: 1. entries coming from main pack covered by bitmap index, and 2. object coming from, possibly alternate, loose or other packs. "2" can be already handled by want_object_in_pack() and to cover "1" we can teach want_object_in_pack() to expect that *found_pack can be non-NULL, meaning calling client already found object's pack entry. In want_object_in_pack() we care to start the checks from already found pack, if we have one, this way determining the answer right away in case neither --local nor --honour-pack-keep are active. In particular, as p5310-pack-bitmaps.sh shows (3 consecutive runs), we do not do harm to served-with-bitmap clones performance-wise: Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.08(8.20+0.25) 9.09(8.14+0.32) +0.1% 5310.3: simulated clone 1.92(2.12+0.08) 1.93(2.12+0.09) +0.5% 5310.4: simulated fetch 0.82(1.07+0.04) 0.82(1.06+0.04) +0.0% 5310.6: partial bitmap 1.96(2.42+0.13) 1.95(2.40+0.15) -0.5% Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.11(8.16+0.32) 9.11(8.19+0.28) +0.0% 5310.3: simulated clone 1.93(2.14+0.07) 1.92(2.11+0.10) -0.5% 5310.4: simulated fetch 0.82(1.06+0.04) 0.82(1.04+0.05) +0.0% 5310.6: partial bitmap 1.95(2.38+0.16) 1.94(2.39+0.14) -0.5% Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.13(8.17+0.31) 9.07(8.13+0.28) -0.7% 5310.3: simulated clone 1.92(2.13+0.07) 1.91(2.12+0.06) -0.5% 5310.4: simulated fetch 0.82(1.08+0.03) 0.82(1.08+0.03) +0.0% 5310.6: partial bitmap 1.96(2.43+0.14) 1.96(2.42+0.14) +0.0% with delta timings showing they are all within noise from run to run. In the general case we do not want to call find_pack_entry_one() more than once, because it is expensive. This patch splits the loop in want_object_in_pack() into two parts: finding the object and seeing if it impacts our choice to include it in the pack. We may call the inexpensive want_found_object() twice, but we will never call find_pack_entry_one() if we do not need to. I appreciate help and discussing this change with Junio C Hamano and Jeff King. Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-09-10 15:01:10 +00:00
# show objects present in pack ($1 should be associated *.idx)
list_packed_objects () {
t5310-pack-bitmaps: fix bogus 'pack-objects to file can use bitmap' test 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>
2018-08-14 11:47:21 +00:00
git show-index <"$1" >object-list &&
cut -d' ' -f2 object-list
pack-objects: respect --local/--honor-pack-keep/--incremental when bitmap is in use Since 6b8fda2d (pack-objects: use bitmaps when packing objects) there are two codepaths in pack-objects: with & without using bitmap reachability index. However add_object_entry_from_bitmap(), despite its non-bitmapped counterpart add_object_entry(), in no way does check for whether --local or --honor-pack-keep or --incremental should be respected. In non-bitmapped codepath this is handled in want_object_in_pack(), but bitmapped codepath has simply no such checking at all. The bitmapped codepath however was allowing to pass in all those options and with bitmap indices still being used under such conditions - potentially giving wrong output (e.g. including objects from non-local or .keep'ed pack). We can easily fix this by noting the following: when an object comes to add_object_entry_from_bitmap() it can come for two reasons: 1. entries coming from main pack covered by bitmap index, and 2. object coming from, possibly alternate, loose or other packs. "2" can be already handled by want_object_in_pack() and to cover "1" we can teach want_object_in_pack() to expect that *found_pack can be non-NULL, meaning calling client already found object's pack entry. In want_object_in_pack() we care to start the checks from already found pack, if we have one, this way determining the answer right away in case neither --local nor --honour-pack-keep are active. In particular, as p5310-pack-bitmaps.sh shows (3 consecutive runs), we do not do harm to served-with-bitmap clones performance-wise: Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.08(8.20+0.25) 9.09(8.14+0.32) +0.1% 5310.3: simulated clone 1.92(2.12+0.08) 1.93(2.12+0.09) +0.5% 5310.4: simulated fetch 0.82(1.07+0.04) 0.82(1.06+0.04) +0.0% 5310.6: partial bitmap 1.96(2.42+0.13) 1.95(2.40+0.15) -0.5% Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.11(8.16+0.32) 9.11(8.19+0.28) +0.0% 5310.3: simulated clone 1.93(2.14+0.07) 1.92(2.11+0.10) -0.5% 5310.4: simulated fetch 0.82(1.06+0.04) 0.82(1.04+0.05) +0.0% 5310.6: partial bitmap 1.95(2.38+0.16) 1.94(2.39+0.14) -0.5% Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.13(8.17+0.31) 9.07(8.13+0.28) -0.7% 5310.3: simulated clone 1.92(2.13+0.07) 1.91(2.12+0.06) -0.5% 5310.4: simulated fetch 0.82(1.08+0.03) 0.82(1.08+0.03) +0.0% 5310.6: partial bitmap 1.96(2.43+0.14) 1.96(2.42+0.14) +0.0% with delta timings showing they are all within noise from run to run. In the general case we do not want to call find_pack_entry_one() more than once, because it is expensive. This patch splits the loop in want_object_in_pack() into two parts: finding the object and seeing if it impacts our choice to include it in the pack. We may call the inexpensive want_found_object() twice, but we will never call find_pack_entry_one() if we do not need to. I appreciate help and discussing this change with Junio C Hamano and Jeff King. Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-09-10 15:01:10 +00:00
}
# has_any pattern-file content-file
# tests whether content-file has any entry from pattern-file with entries being
# whole lines.
has_any () {
grep -Ff "$1" "$2"
}
test_bitmap_cases () {
writeLookupTable=false
for i in "$@"
do
case "$i" in
"pack.writeBitmapLookupTable") writeLookupTable=true;;
esac
done
test_expect_success 'setup test repository' '
rm -fr * .git &&
git init &&
git config pack.writeBitmapLookupTable '"$writeLookupTable"'
'
setup_bitmap_history
test_expect_success 'setup writing bitmaps during repack' '
git config repack.writeBitmaps true
'
test_expect_success 'full repack creates bitmaps' '
GIT_TRACE2_EVENT="$(pwd)/trace" \
git repack -ad &&
ls .git/objects/pack/ | grep bitmap >output &&
test_line_count = 1 output &&
grep "\"key\":\"num_selected_commits\",\"value\":\"106\"" trace &&
grep "\"key\":\"num_maximal_commits\",\"value\":\"107\"" trace
'
basic_bitmap_tests
test_expect_success 'pack-objects respects --local (non-local loose)' '
git init --bare alt.git &&
echo $(pwd)/alt.git/objects >.git/objects/info/alternates &&
echo content1 >file1 &&
# non-local loose object which is not present in bitmapped pack
altblob=$(GIT_DIR=alt.git git hash-object -w file1) &&
# non-local loose object which is also present in bitmapped pack
git cat-file blob $blob | GIT_DIR=alt.git git hash-object -w --stdin &&
git add file1 &&
test_tick &&
git commit -m commit_file1 &&
echo HEAD | git pack-objects --local --stdout --revs >1.pack &&
git index-pack 1.pack &&
list_packed_objects 1.idx >1.objects &&
printf "%s\n" "$altblob" "$blob" >nonlocal-loose &&
! has_any nonlocal-loose 1.objects
'
test_expect_success 'pack-objects respects --honor-pack-keep (local non-bitmapped pack)' '
echo content2 >file2 &&
blob2=$(git hash-object -w file2) &&
git add file2 &&
test_tick &&
git commit -m commit_file2 &&
printf "%s\n" "$blob2" "$bitmaptip" >keepobjects &&
pack2=$(git pack-objects pack2 <keepobjects) &&
mv pack2-$pack2.* .git/objects/pack/ &&
>.git/objects/pack/pack2-$pack2.keep &&
rm $(objpath $blob2) &&
echo HEAD | git pack-objects --honor-pack-keep --stdout --revs >2a.pack &&
git index-pack 2a.pack &&
list_packed_objects 2a.idx >2a.objects &&
! has_any keepobjects 2a.objects
'
test_expect_success 'pack-objects respects --local (non-local pack)' '
mv .git/objects/pack/pack2-$pack2.* alt.git/objects/pack/ &&
echo HEAD | git pack-objects --local --stdout --revs >2b.pack &&
git index-pack 2b.pack &&
list_packed_objects 2b.idx >2b.objects &&
! has_any keepobjects 2b.objects
'
test_expect_success 'pack-objects respects --honor-pack-keep (local bitmapped pack)' '
ls .git/objects/pack/ | grep bitmap >output &&
test_line_count = 1 output &&
packbitmap=$(basename $(cat output) .bitmap) &&
list_packed_objects .git/objects/pack/$packbitmap.idx >packbitmap.objects &&
test_when_finished "rm -f .git/objects/pack/$packbitmap.keep" &&
>.git/objects/pack/$packbitmap.keep &&
echo HEAD | git pack-objects --honor-pack-keep --stdout --revs >3a.pack &&
git index-pack 3a.pack &&
list_packed_objects 3a.idx >3a.objects &&
! has_any packbitmap.objects 3a.objects
'
test_expect_success 'pack-objects respects --local (non-local bitmapped pack)' '
mv .git/objects/pack/$packbitmap.* alt.git/objects/pack/ &&
rm -f .git/objects/pack/multi-pack-index &&
test_when_finished "mv alt.git/objects/pack/$packbitmap.* .git/objects/pack/" &&
echo HEAD | git pack-objects --local --stdout --revs >3b.pack &&
git index-pack 3b.pack &&
list_packed_objects 3b.idx >3b.objects &&
! has_any packbitmap.objects 3b.objects
'
test_expect_success 'pack-objects to file can use bitmap' '
# make sure we still have 1 bitmap index from previous tests
ls .git/objects/pack/ | grep bitmap >output &&
test_line_count = 1 output &&
# verify equivalent packs are generated with/without using bitmap index
packasha1=$(git pack-objects --no-use-bitmap-index --all packa </dev/null) &&
packbsha1=$(git pack-objects --use-bitmap-index --all packb </dev/null) &&
list_packed_objects packa-$packasha1.idx >packa.objects &&
list_packed_objects packb-$packbsha1.idx >packb.objects &&
test_cmp packa.objects packb.objects
'
test_expect_success 'full repack, reusing previous bitmaps' '
pack-bitmap-write: build fewer intermediate bitmaps 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>
2020-12-08 22:04:30 +00:00
git repack -ad &&
ls .git/objects/pack/ | grep bitmap >output &&
test_line_count = 1 output
'
test_expect_success 'fetch (full bitmap)' '
git --git-dir=clone.git fetch origin second:second &&
git rev-parse HEAD >expect &&
git --git-dir=clone.git rev-parse HEAD >actual &&
test_cmp expect actual
'
test_expect_success 'create objects for missing-HAVE tests' '
blob=$(echo "missing have" | git hash-object -w --stdin) &&
tree=$(printf "100644 blob $blob\tfile\n" | git mktree) &&
parent=$(echo parent | git commit-tree $tree) &&
commit=$(echo commit | git commit-tree $tree -p $parent) &&
cat >revs <<-EOF
HEAD
^HEAD^
^$commit
EOF
'
test_expect_success 'pack-objects respects --incremental' '
cat >revs2 <<-EOF &&
HEAD
$commit
EOF
git pack-objects --incremental --stdout --revs <revs2 >4.pack &&
git index-pack 4.pack &&
list_packed_objects 4.idx >4.objects &&
test_line_count = 4 4.objects &&
git rev-list --objects $commit >revlist &&
cut -d" " -f1 revlist |sort >objects &&
test_cmp 4.objects objects
'
test_expect_success 'pack with missing blob' '
rm $(objpath $blob) &&
git pack-objects --stdout --revs <revs >/dev/null
'
test_expect_success 'pack with missing tree' '
rm $(objpath $tree) &&
git pack-objects --stdout --revs <revs >/dev/null
'
test_expect_success 'pack with missing parent' '
rm $(objpath $parent) &&
git pack-objects --stdout --revs <revs >/dev/null
'
test_expect_success JGIT,SHA1 'we can read jgit bitmaps' '
git clone --bare . compat-jgit.git &&
(
cd compat-jgit.git &&
rm -f objects/pack/*.bitmap &&
jgit gc &&
git rev-list --test-bitmap HEAD
)
'
test_expect_success JGIT,SHA1 'jgit can read our bitmaps' '
git clone --bare . compat-us.git &&
(
cd compat-us.git &&
git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
git repack -adb &&
# jgit gc will barf if it does not like our bitmaps
jgit gc
)
'
test_expect_success 'splitting packs does not generate bogus bitmaps' '
test-tool genrandom foo $((1024 * 1024)) >rand &&
git add rand &&
git commit -m "commit with big file" &&
git -c pack.packSizeLimit=500k repack -adb &&
git init --bare no-bitmaps.git &&
git -C no-bitmaps.git fetch .. HEAD
'
test_expect_success 'set up reusable pack' '
rm -f .git/objects/pack/*.keep &&
git repack -adb &&
reusable_pack () {
git for-each-ref --format="%(objectname)" |
git pack-objects --delta-base-offset --revs --stdout "$@"
}
'
test_expect_success 'pack reuse respects --honor-pack-keep' '
test_when_finished "rm -f .git/objects/pack/*.keep" &&
for i in .git/objects/pack/*.pack
do
>${i%.pack}.keep || return 1
done &&
reusable_pack --honor-pack-keep >empty.pack &&
git index-pack empty.pack &&
git show-index <empty.idx >actual &&
test_must_be_empty actual
'
test_expect_success 'pack reuse respects --local' '
mv .git/objects/pack/* alt.git/objects/pack/ &&
test_when_finished "mv alt.git/objects/pack/* .git/objects/pack/" &&
reusable_pack --local >empty.pack &&
git index-pack empty.pack &&
git show-index <empty.idx >actual &&
test_must_be_empty actual
'
test_expect_success 'pack reuse respects --incremental' '
reusable_pack --incremental >empty.pack &&
git index-pack empty.pack &&
git show-index <empty.idx >actual &&
test_must_be_empty actual
'
test_expect_success 'truncated bitmap fails gracefully (ewah)' '
test_config pack.writebitmaphashcache false &&
test_config pack.writebitmaplookuptable false &&
git repack -ad &&
git rev-list --use-bitmap-index --count --all >expect &&
bitmap=$(ls .git/objects/pack/*.bitmap) &&
test_when_finished "rm -f $bitmap" &&
test_copy_bytes 256 <$bitmap >$bitmap.tmp &&
mv -f $bitmap.tmp $bitmap &&
git rev-list --use-bitmap-index --count --all >actual 2>stderr &&
test_cmp expect actual &&
test_grep corrupt.ewah.bitmap stderr
'
test_expect_success 'truncated bitmap fails gracefully (cache)' '
git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
git repack -ad &&
git rev-list --use-bitmap-index --count --all >expect &&
bitmap=$(ls .git/objects/pack/*.bitmap) &&
test_when_finished "rm -f $bitmap" &&
test_copy_bytes 512 <$bitmap >$bitmap.tmp &&
mv -f $bitmap.tmp $bitmap &&
git rev-list --use-bitmap-index --count --all >actual 2>stderr &&
test_cmp expect actual &&
test_grep corrupted.bitmap.index stderr
'
# Create a state of history with these properties:
#
# - refs that allow a client to fetch some new history, while sharing some old
# history with the server; we use branches delta-reuse-old and
# delta-reuse-new here
#
# - the new history contains an object that is stored on the server as a delta
# against a base that is in the old history
#
# - the base object is not immediately reachable from the tip of the old
# history; finding it would involve digging down through history we know the
# other side has
#
# This should result in a state where fetching from old->new would not
# traditionally reuse the on-disk delta (because we'd have to dig to realize
# that the client has it), but we will do so if bitmaps can tell us cheaply
# that the other side has it.
test_expect_success 'set up thin delta-reuse parent' '
# This first commit contains the buried base object.
test-tool genrandom delta 16384 >file &&
git add file &&
git commit -m "delta base" &&
base=$(git rev-parse --verify HEAD:file) &&
# These intermediate commits bury the base back in history.
# This becomes the "old" state.
for i in 1 2 3 4 5
do
echo $i >file &&
git commit -am "intermediate $i" || return 1
done &&
git branch delta-reuse-old &&
# And now our new history has a delta against the buried base. Note
# that this must be smaller than the original file, since pack-objects
# prefers to create deltas from smaller objects to larger.
test-tool genrandom delta 16300 >file &&
git commit -am "delta result" &&
delta=$(git rev-parse --verify HEAD:file) &&
git branch delta-reuse-new &&
# Repack with bitmaps and double check that we have the expected delta
# relationship.
git repack -adb &&
have_delta $delta $base
'
# Now we can sanity-check the non-bitmap behavior (that the server is not able
# to reuse the delta). This isn't strictly something we care about, so this
# test could be scrapped in the future. But it makes sure that the next test is
# actually triggering the feature we want.
#
# Note that our tools for working with on-the-wire "thin" packs are limited. So
# we actually perform the fetch, retain the resulting pack, and inspect the
# result.
test_expect_success 'fetch without bitmaps ignores delta against old base' '
test_config pack.usebitmaps false &&
test_when_finished "rm -rf client.git" &&
git init --bare client.git &&
(
cd client.git &&
git config transfer.unpackLimit 1 &&
git fetch .. delta-reuse-old:delta-reuse-old &&
git fetch .. delta-reuse-new:delta-reuse-new &&
have_delta $delta $ZERO_OID
)
'
# And do the same for the bitmap case, where we do expect to find the delta.
test_expect_success 'fetch with bitmaps can reuse old base' '
test_config pack.usebitmaps true &&
test_when_finished "rm -rf client.git" &&
git init --bare client.git &&
(
cd client.git &&
git config transfer.unpackLimit 1 &&
git fetch .. delta-reuse-old:delta-reuse-old &&
git fetch .. delta-reuse-new:delta-reuse-new &&
have_delta $delta $base
)
'
test_expect_success 'pack.preferBitmapTips' '
git init repo &&
test_when_finished "rm -fr repo" &&
(
cd repo &&
git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
# create enough commits that not all are receive bitmap
# coverage even if they are all at the tip of some reference.
test_commit_bulk --message="%s" 103 &&
git rev-list HEAD >commits.raw &&
sort <commits.raw >commits &&
git log --format="create refs/tags/%s %H" HEAD >refs &&
git update-ref --stdin <refs &&
git repack -adb &&
test-tool bitmap list-commits | sort >bitmaps &&
# remember which commits did not receive bitmaps
comm -13 bitmaps commits >before &&
test_file_not_empty before &&
# mark the commits which did not receive bitmaps as preferred,
# and generate the bitmap again
perl -pe "s{^}{create refs/tags/include/$. }" <before |
git update-ref --stdin &&
git -c pack.preferBitmapTips=refs/tags/include repack -adb &&
# finally, check that the commit(s) without bitmap coverage
# are not the same ones as before
test-tool bitmap list-commits | sort >bitmaps &&
comm -13 bitmaps commits >after &&
! test_cmp before after
)
'
config API: add "string" version of *_value_multi(), fix segfaults 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: - d811c8e17c6 (versionsort: support reorder prerelease suffixes, 2015-02-26) - c026557a373 (versioncmp: generalize version sort suffix reordering, 2016-12-08) - a086f921a72 (submodule: decouple url and submodule interest, 2017-03-17) - a6be5e6764a (log: add log.excludeDecoration config option, 2020-04-16) - 92156291ca8 (log: add default decoration filter, 2022-08-05) - 50a044f1e40 (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. 40ea4ed9032 (Add config_error_nonbool() helper function, 2008-02-11) 2. 6c47d0e8f39 (config.c: guard config parser from value=NULL, 2008-02-11). 3. 4c715ebb96a (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>
2023-03-28 14:04:27 +00:00
test_expect_success 'pack.preferBitmapTips' '
git init repo &&
test_when_finished "rm -rf repo" &&
(
cd repo &&
git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
test_commit_bulk --message="%s" 103 &&
cat >>.git/config <<-\EOF &&
[pack]
preferBitmapTips
EOF
config API: add "string" version of *_value_multi(), fix segfaults 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: - d811c8e17c6 (versionsort: support reorder prerelease suffixes, 2015-02-26) - c026557a373 (versioncmp: generalize version sort suffix reordering, 2016-12-08) - a086f921a72 (submodule: decouple url and submodule interest, 2017-03-17) - a6be5e6764a (log: add log.excludeDecoration config option, 2020-04-16) - 92156291ca8 (log: add default decoration filter, 2022-08-05) - 50a044f1e40 (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. 40ea4ed9032 (Add config_error_nonbool() helper function, 2008-02-11) 2. 6c47d0e8f39 (config.c: guard config parser from value=NULL, 2008-02-11). 3. 4c715ebb96a (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>
2023-03-28 14:04:27 +00:00
cat >expect <<-\EOF &&
error: missing value for '\''pack.preferbitmaptips'\''
EOF
git repack -adb 2>actual &&
test_cmp expect actual
)
'
test_expect_success 'complains about multiple pack bitmaps' '
rm -fr repo &&
git init repo &&
test_when_finished "rm -fr repo" &&
(
cd repo &&
git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
test_commit base &&
git repack -adb &&
bitmap="$(ls .git/objects/pack/pack-*.bitmap)" &&
mv "$bitmap" "$bitmap.bak" &&
test_commit other &&
git repack -ab &&
mv "$bitmap.bak" "$bitmap" &&
find .git/objects/pack -type f -name "*.pack" >packs &&
find .git/objects/pack -type f -name "*.bitmap" >bitmaps &&
test_line_count = 2 packs &&
test_line_count = 2 bitmaps &&
GIT_TRACE2_EVENT=$(pwd)/trace2.txt git rev-list --use-bitmap-index HEAD &&
grep "opened bitmap" trace2.txt &&
grep "ignoring extra bitmap" trace2.txt
)
'
}
test_bitmap_cases
pack-bitmap.c: use commit boundary during bitmap traversal 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>
2023-05-08 17:38:12 +00:00
GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL=1
export GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL
test_bitmap_cases
sane_unset GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL
test_expect_success 'incremental repack fails when bitmaps are requested' '
test_commit more-1 &&
test_must_fail git repack -d 2>err &&
test_grep "Incremental repacks are incompatible with bitmap" err
'
test_expect_success 'incremental repack can disable bitmaps' '
test_commit more-2 &&
git repack -d --no-write-bitmap-index
'
pack-bitmap.c: use commit boundary during bitmap traversal 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>
2023-05-08 17:38:12 +00:00
test_expect_success 'boundary-based traversal is used when requested' '
git repack -a -d --write-bitmap-index &&
for argv in \
"git -c pack.useBitmapBoundaryTraversal=true" \
"git -c feature.experimental=true" \
"GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL=1 git"
do
eval "GIT_TRACE2_EVENT=1 $argv rev-list --objects \
--use-bitmap-index second..other 2>perf" &&
grep "\"region_enter\".*\"label\":\"haves/boundary\"" perf ||
return 1
done &&
for argv in \
"git -c pack.useBitmapBoundaryTraversal=false" \
"git -c feature.experimental=true -c pack.useBitmapBoundaryTraversal=false" \
"GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL=0 git -c pack.useBitmapBoundaryTraversal=true" \
"GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL=0 git -c feature.experimental=true"
do
eval "GIT_TRACE2_EVENT=1 $argv rev-list --objects \
--use-bitmap-index second..other 2>perf" &&
grep "\"region_enter\".*\"label\":\"haves/classic\"" perf ||
return 1
done
'
test_bitmap_cases "pack.writeBitmapLookupTable"
add `ignore_missing_links` mode to revwalk When pack-objects is computing the reachability bitmap to serve a fetch request, it can erroneously die() if some of the UNINTERESTING objects are not present. Upload-pack throws away HAVE lines from the client for objects we do not have, but we may have a tip object without all of its ancestors (e.g., if the tip is no longer reachable and was new enough to survive a `git prune`, but some of its reachable objects did get pruned). In the non-bitmap case, we do a revision walk with the HAVE objects marked as UNINTERESTING. The revision walker explicitly ignores errors in accessing UNINTERESTING commits to handle this case (and we do not bother looking at UNINTERESTING trees or blobs at all). When we have bitmaps, however, the process is quite different. The bitmap index for a pack-objects run is calculated in two separate steps: First, we perform an extensive walk from all the HAVEs to find the full set of objects reachable from them. This walk is usually optimized away because we are expected to hit an object with a bitmap during the traversal, which allows us to terminate early. Secondly, we perform an extensive walk from all the WANTs, which usually also terminates early because we hit a commit with an existing bitmap. Once we have the resulting bitmaps from the two walks, we AND-NOT them together to obtain the resulting set of objects we need to pack. When we are walking the HAVE objects, the revision walker does not know that we are walking it only to mark the results as uninteresting. We strip out the UNINTERESTING flag, because those objects _are_ interesting to us during the first walk. We want to keep going to get a complete set of reachable objects if we can. We need some way to tell the revision walker that it's OK to silently truncate the HAVE walk, just like it does for the UNINTERESTING case. This patch introduces a new `ignore_missing_links` flag to the `rev_info` struct, which we set only for the HAVE walk. It also adds tests to cover UNINTERESTING objects missing from several positions: a missing blob, a missing tree, and a missing parent commit. The missing blob already worked (as we do not care about its contents at all), but the other two cases caused us to die(). Note that there are a few cases we do not need to test: 1. We do not need to test a missing tree, with the blob still present. Without the tree that refers to it, we would not know that the blob is relevant to our walk. 2. We do not need to test a tip commit that is missing. Upload-pack omits these for us (and in fact, we complain even in the non-bitmap case if it fails to do so). Reported-by: Siddharth Agarwal <sid0@fb.com> Signed-off-by: Vicent Marti <tanoku@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2014-03-28 10:00:43 +00:00
test_expect_success 'verify writing bitmap lookup table when enabled' '
GIT_TRACE2_EVENT="$(pwd)/trace2" \
git repack -ad &&
grep "\"label\":\"writing_lookup_table\"" trace2
pack-bitmap.c: gracefully fallback after opening pack/MIDX 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>
2022-01-25 22:41:20 +00:00
'
test_expect_success 'truncated bitmap fails gracefully (lookup table)' '
test_config pack.writebitmaphashcache false &&
git repack -adb &&
git rev-list --use-bitmap-index --count --all >expect &&
bitmap=$(ls .git/objects/pack/*.bitmap) &&
test_when_finished "rm -f $bitmap" &&
test_copy_bytes 512 <$bitmap >$bitmap.tmp &&
mv -f $bitmap.tmp $bitmap &&
git rev-list --use-bitmap-index --count --all >actual 2>stderr &&
test_cmp expect actual &&
test_grep corrupted.bitmap.index stderr
'
test_done