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645c432d61
Starting from 6b8fda2d (pack-objects: use bitmaps when packing objects)
if a repository has bitmap index, pack-objects can nicely speedup
"Counting objects" graph traversal phase. That however was done only for
case when resultant pack is sent to stdout, not written into a file.
The reason here is for on-disk repack by default we want:
- to produce good pack (with bitmap index not-yet-packed objects are
emitted to pack in suboptimal order).
- to use more robust pack-generation codepath (avoiding possible
bugs in bitmap code and possible bitmap index corruption).
Jeff King further explains:
The reason for this split is that pack-objects tries to determine how
"careful" it should be based on whether we are packing to disk or to
stdout. Packing to disk implies "git repack", and that we will likely
delete the old packs after finishing. We want to be more careful (so
as not to carry forward a corruption, and to generate a more optimal
pack), and we presumably run less frequently and can afford extra CPU.
Whereas packing to stdout implies serving a remote via "git fetch" or
"git push". This happens more frequently (e.g., a server handling many
fetching clients), and we assume the receiving end takes more
responsibility for verifying the data.
But this isn't always the case. One might want to generate on-disk
packfiles for a specialized object transfer. Just using "--stdout" and
writing to a file is not optimal, as it will not generate the matching
pack index.
So it would be useful to have some way of overriding this heuristic:
to tell pack-objects that even though it should generate on-disk
files, it is still OK to use the reachability bitmaps to do the
traversal.
So we can teach pack-objects to use bitmap index for initial object
counting phase when generating resultant pack file too:
- if we take care to not let it be activated under git-repack:
See above about repack robustness and not forward-carrying corruption.
- if we know bitmap index generation is not enabled for resultant pack:
The current code has singleton bitmap_git, so it cannot work
simultaneously with two bitmap indices.
We also want to avoid (at least with current implementation)
generating bitmaps off of bitmaps. The reason here is: when generating
a pack, not-yet-packed objects will be emitted into pack in
suboptimal order and added to tail of the bitmap as "extended entries".
When the resultant pack + some new objects in associated repository
are in turn used to generate another pack with bitmap, the situation
repeats: new objects are again not emitted optimally and just added to
bitmap tail - not in recency order.
So the pack badness can grow over time when at each step we have
bitmapped pack + some other objects. That's why we want to avoid
generating bitmaps off of bitmaps, not to let pack badness grow.
- if we keep pack reuse enabled still only for "send-to-stdout" case:
Because pack-to-file needs to generate index for destination pack, and
currently on pack reuse raw entries are directly written out to the
destination pack by write_reused_pack(), bypassing needed for pack index
generation bookkeeping done by regular codepath in write_one() and
friends.
( In the future we might teach pack-reuse code about cases when index
also needs to be generated for resultant pack and remove
pack-reuse-only-for-stdout limitation )
This way for pack-objects -> file we get nice speedup:
erp5.git[1] (~230MB) extracted from ~ 5GB lab.nexedi.com backup
repository managed by git-backup[2] via
time echo 0186ac99 | git pack-objects --revs erp5pack
before: 37.2s
after: 26.2s
And for `git repack -adb` packed git.git
time echo 5c589a73 | git pack-objects --revs gitpack
before: 7.1s
after: 3.6s
i.e. it can be 30% - 50% speedup for pack extraction.
git-backup extracts many packs on repositories restoration. That was my
initial motivation for the patch.
[1] https://lab.nexedi.com/nexedi/erp5
[2] https://lab.nexedi.com/kirr/git-backup
NOTE
Jeff also suggests that pack.useBitmaps was probably a mistake to
introduce originally. This way we are not adding another config point,
but instead just always default to-file pack-objects not to use bitmap
index: Tools which need to generate on-disk packs with using bitmap, can
pass --use-bitmap-index explicitly. And git-repack does never pass
--use-bitmap-index, so this way we can be sure regular on-disk repacking
remains robust.
NOTE2
`git pack-objects --stdout >file.pack` + `git index-pack file.pack` is much slower
than `git pack-objects file.pack`. Extracting erp5.git pack from
lab.nexedi.com backup repository:
$ time echo 0186ac99 | git pack-objects --stdout --revs >erp5pack-stdout.pack
real 0m22.309s
user 0m21.148s
sys 0m0.932s
$ time git index-pack erp5pack-stdout.pack
real 0m50.873s <-- more than 2 times slower than time to generate pack itself!
user 0m49.300s
sys 0m1.360s
So the time for
`pack-object --stdout >file.pack` + `index-pack file.pack` is 72s,
while
`pack-objects file.pack` which does both pack and index is 27s.
And even
`pack-objects --no-use-bitmap-index file.pack` is 37s.
Jeff explains:
The packfile does not carry the sha1 of the objects. A receiving
index-pack has to compute them itself, including inflating and applying
all of the deltas.
that's why for `git-backup restore` we want to teach `git pack-objects
file.pack` to use bitmaps instead of using `git pack-objects --stdout
>file.pack` + `git index-pack file.pack`.
NOTE3
The speedup is now tracked via t/perf/p5310-pack-bitmaps.sh
Test 56dfeb62 this tree
--------------------------------------------------------------------------------
5310.2: repack to disk 8.98(8.05+0.29) 9.05(8.08+0.33) +0.8%
5310.3: simulated clone 2.02(2.27+0.09) 2.01(2.25+0.08) -0.5%
5310.4: simulated fetch 0.81(1.07+0.02) 0.81(1.05+0.04) +0.0%
5310.5: pack to file 7.58(7.04+0.28) 7.60(7.04+0.30) +0.3%
5310.6: pack to file (bitmap) 7.55(7.02+0.28) 3.25(2.82+0.18) -57.0%
5310.8: clone (partial bitmap) 1.83(2.26+0.12) 1.82(2.22+0.14) -0.5%
5310.9: pack to file (partial bitmap) 6.86(6.58+0.30) 2.87(2.74+0.20) -58.2%
More context:
http://marc.info/?t=146792101400001&r=1&w=2
http://public-inbox.org/git/20160707190917.20011-1-kirr@nexedi.com/T/#t
Cc: Vicent Marti <tanoku@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
299 lines
8.9 KiB
Bash
Executable File
299 lines
8.9 KiB
Bash
Executable File
#!/bin/sh
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test_description='exercise basic bitmap functionality'
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. ./test-lib.sh
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objpath () {
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echo ".git/objects/$(echo "$1" | sed -e 's|\(..\)|\1/|')"
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}
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# show objects present in pack ($1 should be associated *.idx)
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list_packed_objects () {
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git show-index <"$1" | cut -d' ' -f2
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}
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# has_any pattern-file content-file
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# tests whether content-file has any entry from pattern-file with entries being
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# whole lines.
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has_any () {
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grep -Ff "$1" "$2"
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}
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test_expect_success 'setup repo with moderate-sized history' '
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for i in $(test_seq 1 10); do
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test_commit $i
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done &&
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git checkout -b other HEAD~5 &&
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for i in $(test_seq 1 10); do
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test_commit side-$i
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done &&
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git checkout master &&
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bitmaptip=$(git rev-parse master) &&
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blob=$(echo tagged-blob | git hash-object -w --stdin) &&
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git tag tagged-blob $blob &&
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git config repack.writebitmaps true &&
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git config pack.writebitmaphashcache true
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'
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test_expect_success 'full repack creates bitmaps' '
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git repack -ad &&
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ls .git/objects/pack/ | grep bitmap >output &&
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test_line_count = 1 output
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'
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test_expect_success 'rev-list --test-bitmap verifies bitmaps' '
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git rev-list --test-bitmap HEAD
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'
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rev_list_tests() {
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state=$1
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test_expect_success "counting commits via bitmap ($state)" '
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git rev-list --count HEAD >expect &&
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git rev-list --use-bitmap-index --count HEAD >actual &&
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test_cmp expect actual
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'
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test_expect_success "counting partial commits via bitmap ($state)" '
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git rev-list --count HEAD~5..HEAD >expect &&
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git rev-list --use-bitmap-index --count HEAD~5..HEAD >actual &&
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test_cmp expect actual
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'
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test_expect_success "counting commits with limit ($state)" '
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git rev-list --count -n 1 HEAD >expect &&
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git rev-list --use-bitmap-index --count -n 1 HEAD >actual &&
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test_cmp expect actual
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'
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test_expect_success "counting non-linear history ($state)" '
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git rev-list --count other...master >expect &&
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git rev-list --use-bitmap-index --count other...master >actual &&
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test_cmp expect actual
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'
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test_expect_success "counting commits with limiting ($state)" '
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git rev-list --count HEAD -- 1.t >expect &&
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git rev-list --use-bitmap-index --count HEAD -- 1.t >actual &&
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test_cmp expect actual
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'
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test_expect_success "enumerate --objects ($state)" '
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git rev-list --objects --use-bitmap-index HEAD >tmp &&
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cut -d" " -f1 <tmp >tmp2 &&
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sort <tmp2 >actual &&
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git rev-list --objects HEAD >tmp &&
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cut -d" " -f1 <tmp >tmp2 &&
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sort <tmp2 >expect &&
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test_cmp expect actual
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'
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test_expect_success "bitmap --objects handles non-commit objects ($state)" '
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git rev-list --objects --use-bitmap-index HEAD tagged-blob >actual &&
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grep $blob actual
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'
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}
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rev_list_tests 'full bitmap'
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test_expect_success 'clone from bitmapped repository' '
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git clone --no-local --bare . clone.git &&
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git rev-parse HEAD >expect &&
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git --git-dir=clone.git rev-parse HEAD >actual &&
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test_cmp expect actual
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'
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test_expect_success 'setup further non-bitmapped commits' '
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for i in $(test_seq 1 10); do
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test_commit further-$i
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done
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'
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rev_list_tests 'partial bitmap'
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test_expect_success 'fetch (partial bitmap)' '
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git --git-dir=clone.git fetch origin master:master &&
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git rev-parse HEAD >expect &&
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git --git-dir=clone.git rev-parse HEAD >actual &&
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test_cmp expect actual
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'
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test_expect_success 'incremental repack cannot create bitmaps' '
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test_commit more-1 &&
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find .git/objects/pack -name "*.bitmap" >expect &&
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git repack -d &&
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find .git/objects/pack -name "*.bitmap" >actual &&
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test_cmp expect actual
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'
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test_expect_success 'incremental repack can disable bitmaps' '
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test_commit more-2 &&
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git repack -d --no-write-bitmap-index
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'
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test_expect_success 'pack-objects respects --local (non-local loose)' '
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git init --bare alt.git &&
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echo $(pwd)/alt.git/objects >.git/objects/info/alternates &&
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echo content1 >file1 &&
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# non-local loose object which is not present in bitmapped pack
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altblob=$(GIT_DIR=alt.git git hash-object -w file1) &&
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# non-local loose object which is also present in bitmapped pack
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git cat-file blob $blob | GIT_DIR=alt.git git hash-object -w --stdin &&
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git add file1 &&
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test_tick &&
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git commit -m commit_file1 &&
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echo HEAD | git pack-objects --local --stdout --revs >1.pack &&
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git index-pack 1.pack &&
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list_packed_objects 1.idx >1.objects &&
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printf "%s\n" "$altblob" "$blob" >nonlocal-loose &&
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! has_any nonlocal-loose 1.objects
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'
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test_expect_success 'pack-objects respects --honor-pack-keep (local non-bitmapped pack)' '
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echo content2 >file2 &&
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blob2=$(git hash-object -w file2) &&
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git add file2 &&
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test_tick &&
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git commit -m commit_file2 &&
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printf "%s\n" "$blob2" "$bitmaptip" >keepobjects &&
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pack2=$(git pack-objects pack2 <keepobjects) &&
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mv pack2-$pack2.* .git/objects/pack/ &&
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>.git/objects/pack/pack2-$pack2.keep &&
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rm $(objpath $blob2) &&
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echo HEAD | git pack-objects --honor-pack-keep --stdout --revs >2a.pack &&
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git index-pack 2a.pack &&
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list_packed_objects 2a.idx >2a.objects &&
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! has_any keepobjects 2a.objects
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'
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test_expect_success 'pack-objects respects --local (non-local pack)' '
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mv .git/objects/pack/pack2-$pack2.* alt.git/objects/pack/ &&
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echo HEAD | git pack-objects --local --stdout --revs >2b.pack &&
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git index-pack 2b.pack &&
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list_packed_objects 2b.idx >2b.objects &&
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! has_any keepobjects 2b.objects
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'
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test_expect_success 'pack-objects respects --honor-pack-keep (local bitmapped pack)' '
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ls .git/objects/pack/ | grep bitmap >output &&
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test_line_count = 1 output &&
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packbitmap=$(basename $(cat output) .bitmap) &&
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list_packed_objects .git/objects/pack/$packbitmap.idx >packbitmap.objects &&
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test_when_finished "rm -f .git/objects/pack/$packbitmap.keep" &&
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>.git/objects/pack/$packbitmap.keep &&
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echo HEAD | git pack-objects --honor-pack-keep --stdout --revs >3a.pack &&
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git index-pack 3a.pack &&
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list_packed_objects 3a.idx >3a.objects &&
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! has_any packbitmap.objects 3a.objects
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'
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test_expect_success 'pack-objects respects --local (non-local bitmapped pack)' '
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mv .git/objects/pack/$packbitmap.* alt.git/objects/pack/ &&
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test_when_finished "mv alt.git/objects/pack/$packbitmap.* .git/objects/pack/" &&
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echo HEAD | git pack-objects --local --stdout --revs >3b.pack &&
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git index-pack 3b.pack &&
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list_packed_objects 3b.idx >3b.objects &&
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! has_any packbitmap.objects 3b.objects
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'
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test_expect_success 'pack-objects to file can use bitmap' '
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# make sure we still have 1 bitmap index from previous tests
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ls .git/objects/pack/ | grep bitmap >output &&
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test_line_count = 1 output &&
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# verify equivalent packs are generated with/without using bitmap index
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packasha1=$(git pack-objects --no-use-bitmap-index --all packa </dev/null) &&
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packbsha1=$(git pack-objects --use-bitmap-index --all packb </dev/null) &&
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list_packed_objects <packa-$packasha1.idx >packa.objects &&
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list_packed_objects <packb-$packbsha1.idx >packb.objects &&
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test_cmp packa.objects packb.objects
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'
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test_expect_success 'full repack, reusing previous bitmaps' '
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git repack -ad &&
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ls .git/objects/pack/ | grep bitmap >output &&
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test_line_count = 1 output
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'
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test_expect_success 'fetch (full bitmap)' '
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git --git-dir=clone.git fetch origin master:master &&
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git rev-parse HEAD >expect &&
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git --git-dir=clone.git rev-parse HEAD >actual &&
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test_cmp expect actual
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'
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test_expect_success 'create objects for missing-HAVE tests' '
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blob=$(echo "missing have" | git hash-object -w --stdin) &&
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tree=$(printf "100644 blob $blob\tfile\n" | git mktree) &&
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parent=$(echo parent | git commit-tree $tree) &&
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commit=$(echo commit | git commit-tree $tree -p $parent) &&
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cat >revs <<-EOF
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HEAD
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^HEAD^
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^$commit
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EOF
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'
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test_expect_success 'pack-objects respects --incremental' '
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cat >revs2 <<-EOF &&
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HEAD
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$commit
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EOF
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git pack-objects --incremental --stdout --revs <revs2 >4.pack &&
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git index-pack 4.pack &&
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list_packed_objects 4.idx >4.objects &&
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test_line_count = 4 4.objects &&
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git rev-list --objects $commit >revlist &&
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cut -d" " -f1 revlist |sort >objects &&
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test_cmp 4.objects objects
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'
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test_expect_success 'pack with missing blob' '
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rm $(objpath $blob) &&
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git pack-objects --stdout --revs <revs >/dev/null
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'
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test_expect_success 'pack with missing tree' '
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rm $(objpath $tree) &&
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git pack-objects --stdout --revs <revs >/dev/null
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'
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test_expect_success 'pack with missing parent' '
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rm $(objpath $parent) &&
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git pack-objects --stdout --revs <revs >/dev/null
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'
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test_lazy_prereq JGIT '
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type jgit
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'
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test_expect_success JGIT 'we can read jgit bitmaps' '
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git clone . compat-jgit &&
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(
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cd compat-jgit &&
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rm -f .git/objects/pack/*.bitmap &&
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jgit gc &&
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git rev-list --test-bitmap HEAD
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)
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'
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test_expect_success JGIT 'jgit can read our bitmaps' '
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git clone . compat-us &&
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(
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cd compat-us &&
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git repack -adb &&
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# jgit gc will barf if it does not like our bitmaps
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jgit gc
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)
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'
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test_expect_success 'splitting packs does not generate bogus bitmaps' '
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test-genrandom foo $((1024 * 1024)) >rand &&
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git add rand &&
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git commit -m "commit with big file" &&
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git -c pack.packSizeLimit=500k repack -adb &&
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git init --bare no-bitmaps.git &&
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git -C no-bitmaps.git fetch .. HEAD
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'
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test_done
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