mirror of https://github.com/git/git.git
unpack-objects: use stream_loose_object() to unpack large objects
Make use of the stream_loose_object() function introduced in the preceding commit to unpack large objects. Before this we'd need to malloc() the size of the blob before unpacking it, which could cause OOM with very large blobs. We could use the new streaming interface to unpack all blobs, but doing so would be much slower, as demonstrated e.g. with this benchmark using git-hyperfine[0]: rm -rf /tmp/scalar.git && git clone --bare https://github.com/Microsoft/scalar.git /tmp/scalar.git && mv /tmp/scalar.git/objects/pack/*.pack /tmp/scalar.git/my.pack && git hyperfine \ -r 2 --warmup 1 \ -L rev origin/master,HEAD -L v "10,512,1k,1m" \ -s 'make' \ -p 'git init --bare dest.git' \ -c 'rm -rf dest.git' \ './git -C dest.git -c core.bigFileThreshold={v} unpack-objects </tmp/scalar.git/my.pack' Here we'll perform worse with lower core.bigFileThreshold settings with this change in terms of speed, but we're getting lower memory use in return: Summary './git -C dest.git -c core.bigFileThreshold=10 unpack-objects </tmp/scalar.git/my.pack' in 'origin/master' ran 1.01 ± 0.01 times faster than './git -C dest.git -c core.bigFileThreshold=1k unpack-objects </tmp/scalar.git/my.pack' in 'origin/master' 1.01 ± 0.01 times faster than './git -C dest.git -c core.bigFileThreshold=1m unpack-objects </tmp/scalar.git/my.pack' in 'origin/master' 1.01 ± 0.02 times faster than './git -C dest.git -c core.bigFileThreshold=1m unpack-objects </tmp/scalar.git/my.pack' in 'HEAD' 1.02 ± 0.00 times faster than './git -C dest.git -c core.bigFileThreshold=512 unpack-objects </tmp/scalar.git/my.pack' in 'origin/master' 1.09 ± 0.01 times faster than './git -C dest.git -c core.bigFileThreshold=1k unpack-objects </tmp/scalar.git/my.pack' in 'HEAD' 1.10 ± 0.00 times faster than './git -C dest.git -c core.bigFileThreshold=512 unpack-objects </tmp/scalar.git/my.pack' in 'HEAD' 1.11 ± 0.00 times faster than './git -C dest.git -c core.bigFileThreshold=10 unpack-objects </tmp/scalar.git/my.pack' in 'HEAD' A better benchmark to demonstrate the benefits of that this one, which creates an artificial repo with a 1, 25, 50, 75 and 100MB blob: rm -rf /tmp/repo && git init /tmp/repo && ( cd /tmp/repo && for i in 1 25 50 75 100 do dd if=/dev/urandom of=blob.$i count=$(($i*1024)) bs=1024 done && git add blob.* && git commit -mblobs && git gc && PACK=$(echo .git/objects/pack/pack-*.pack) && cp "$PACK" my.pack ) && git hyperfine \ --show-output \ -L rev origin/master,HEAD -L v "512,50m,100m" \ -s 'make' \ -p 'git init --bare dest.git' \ -c 'rm -rf dest.git' \ '/usr/bin/time -v ./git -C dest.git -c core.bigFileThreshold={v} unpack-objects </tmp/repo/my.pack 2>&1 | grep Maximum' Using this test we'll always use >100MB of memory on origin/master (around ~105MB), but max out at e.g. ~55MB if we set core.bigFileThreshold=50m. The relevant "Maximum resident set size" lines were manually added below the relevant benchmark: '/usr/bin/time -v ./git -C dest.git -c core.bigFileThreshold=50m unpack-objects </tmp/repo/my.pack 2>&1 | grep Maximum' in 'origin/master' ran Maximum resident set size (kbytes): 107080 1.02 ± 0.78 times faster than '/usr/bin/time -v ./git -C dest.git -c core.bigFileThreshold=512 unpack-objects </tmp/repo/my.pack 2>&1 | grep Maximum' in 'origin/master' Maximum resident set size (kbytes): 106968 1.09 ± 0.79 times faster than '/usr/bin/time -v ./git -C dest.git -c core.bigFileThreshold=100m unpack-objects </tmp/repo/my.pack 2>&1 | grep Maximum' in 'origin/master' Maximum resident set size (kbytes): 107032 1.42 ± 1.07 times faster than '/usr/bin/time -v ./git -C dest.git -c core.bigFileThreshold=100m unpack-objects </tmp/repo/my.pack 2>&1 | grep Maximum' in 'HEAD' Maximum resident set size (kbytes): 107072 1.83 ± 1.02 times faster than '/usr/bin/time -v ./git -C dest.git -c core.bigFileThreshold=50m unpack-objects </tmp/repo/my.pack 2>&1 | grep Maximum' in 'HEAD' Maximum resident set size (kbytes): 55704 2.16 ± 1.19 times faster than '/usr/bin/time -v ./git -C dest.git -c core.bigFileThreshold=512 unpack-objects </tmp/repo/my.pack 2>&1 | grep Maximum' in 'HEAD' Maximum resident set size (kbytes): 4564 This shows that if you have enough memory this new streaming method is slower the lower you set the streaming threshold, but the benefit is more bounded memory use. An earlier version of this patch introduced a new "core.bigFileStreamingThreshold" instead of re-using the existing "core.bigFileThreshold" variable[1]. As noted in a detailed overview of its users in [2] using it has several different meanings. Still, we consider it good enough to simply re-use it. While it's possible that someone might want to e.g. consider objects "small" for the purposes of diffing but "big" for the purposes of writing them such use-cases are probably too obscure to worry about. We can always split up "core.bigFileThreshold" in the future if there's a need for that. 0. https://github.com/avar/git-hyperfine/ 1. https://lore.kernel.org/git/20211210103435.83656-1-chiyutianyi@gmail.com/ 2. https://lore.kernel.org/git/20220120112114.47618-5-chiyutianyi@gmail.com/ Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Helped-by: Derrick Stolee <stolee@gmail.com> Helped-by: Jiang Xin <zhiyou.jx@alibaba-inc.com> Signed-off-by: Han Xin <chiyutianyi@gmail.com> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Han Xin
Junio C Hamano
parent
3c3ca0b0c1
commit
aaf81223f4
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@ -468,8 +468,8 @@ usage, at the slight expense of increased disk usage.
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* Will generally be streamed when written, which avoids excessive
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memory usage, at the cost of some fixed overhead. Commands that make
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use of this include linkgit:git-archive[1],
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linkgit:git-fast-import[1], linkgit:git-index-pack[1] and
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linkgit:git-fsck[1].
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linkgit:git-fast-import[1], linkgit:git-index-pack[1],
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linkgit:git-unpack-objects[1] and linkgit:git-fsck[1].
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core.excludesFile::
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Specifies the pathname to the file that contains patterns to
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@ -351,6 +351,68 @@ static void unpack_non_delta_entry(enum object_type type, unsigned long size,
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write_object(nr, type, buf, size);
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}
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struct input_zstream_data {
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git_zstream *zstream;
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unsigned char buf[8192];
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int status;
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};
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static const void *feed_input_zstream(struct input_stream *in_stream,
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unsigned long *readlen)
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{
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struct input_zstream_data *data = in_stream->data;
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git_zstream *zstream = data->zstream;
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void *in = fill(1);
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if (in_stream->is_finished) {
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*readlen = 0;
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return NULL;
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}
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zstream->next_out = data->buf;
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zstream->avail_out = sizeof(data->buf);
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zstream->next_in = in;
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zstream->avail_in = len;
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data->status = git_inflate(zstream, 0);
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in_stream->is_finished = data->status != Z_OK;
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use(len - zstream->avail_in);
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*readlen = sizeof(data->buf) - zstream->avail_out;
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return data->buf;
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}
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static void stream_blob(unsigned long size, unsigned nr)
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{
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git_zstream zstream = { 0 };
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struct input_zstream_data data = { 0 };
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struct input_stream in_stream = {
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.read = feed_input_zstream,
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.data = &data,
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};
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struct obj_info *info = &obj_list[nr];
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data.zstream = &zstream;
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git_inflate_init(&zstream);
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if (stream_loose_object(&in_stream, size, &info->oid))
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die(_("failed to write object in stream"));
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if (data.status != Z_STREAM_END)
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die(_("inflate returned (%d)"), data.status);
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git_inflate_end(&zstream);
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if (strict) {
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struct blob *blob = lookup_blob(the_repository, &info->oid);
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if (!blob)
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die(_("invalid blob object from stream"));
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blob->object.flags |= FLAG_WRITTEN;
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}
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info->obj = NULL;
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}
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static int resolve_against_held(unsigned nr, const struct object_id *base,
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void *delta_data, unsigned long delta_size)
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{
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@ -483,9 +545,14 @@ static void unpack_one(unsigned nr)
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}
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switch (type) {
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case OBJ_BLOB:
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if (!dry_run && size > big_file_threshold) {
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stream_blob(size, nr);
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return;
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}
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/* fallthrough */
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case OBJ_COMMIT:
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case OBJ_TREE:
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case OBJ_BLOB:
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case OBJ_TAG:
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unpack_non_delta_entry(type, size, nr);
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return;
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@ -9,7 +9,8 @@ test_description='git unpack-objects with large objects'
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prepare_dest () {
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test_when_finished "rm -rf dest.git" &&
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git init --bare dest.git
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git init --bare dest.git &&
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git -C dest.git config core.bigFileThreshold "$1"
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}
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test_expect_success "create large objects (1.5 MB) and PACK" '
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@ -17,7 +18,10 @@ test_expect_success "create large objects (1.5 MB) and PACK" '
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test_commit --append foo big-blob &&
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test-tool genrandom bar 1500000 >big-blob &&
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test_commit --append bar big-blob &&
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PACK=$(echo HEAD | git pack-objects --revs pack)
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PACK=$(echo HEAD | git pack-objects --revs pack) &&
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git verify-pack -v pack-$PACK.pack >out &&
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sed -n -e "s/^\([0-9a-f][0-9a-f]*\).*\(commit\|tree\|blob\).*/\1/p" \
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<out >obj-list
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'
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test_expect_success 'set memory limitation to 1MB' '
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@ -26,16 +30,47 @@ test_expect_success 'set memory limitation to 1MB' '
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'
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test_expect_success 'unpack-objects failed under memory limitation' '
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prepare_dest &&
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prepare_dest 2m &&
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test_must_fail git -C dest.git unpack-objects <pack-$PACK.pack 2>err &&
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grep "fatal: attempting to allocate" err
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'
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test_expect_success 'unpack-objects works with memory limitation in dry-run mode' '
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prepare_dest &&
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prepare_dest 2m &&
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git -C dest.git unpack-objects -n <pack-$PACK.pack &&
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test_stdout_line_count = 0 find dest.git/objects -type f &&
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test_dir_is_empty dest.git/objects/pack
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'
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test_expect_success 'unpack big object in stream' '
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prepare_dest 1m &&
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git -C dest.git unpack-objects <pack-$PACK.pack &&
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test_dir_is_empty dest.git/objects/pack
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'
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BATCH_CONFIGURATION='-c core.fsync=loose-object -c core.fsyncmethod=batch'
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test_expect_success 'unpack big object in stream (core.fsyncmethod=batch)' '
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prepare_dest 1m &&
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GIT_TRACE2_EVENT="$(pwd)/trace2.txt" \
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git -C dest.git $BATCH_CONFIGURATION unpack-objects <pack-$PACK.pack &&
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grep fsync/hardware-flush trace2.txt &&
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test_dir_is_empty dest.git/objects/pack &&
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git -C dest.git cat-file --batch-check="%(objectname)" <obj-list >current &&
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cmp obj-list current
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'
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test_expect_success 'do not unpack existing large objects' '
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prepare_dest 1m &&
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git -C dest.git index-pack --stdin <pack-$PACK.pack &&
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git -C dest.git unpack-objects <pack-$PACK.pack &&
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# The destination came up with the exact same pack...
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DEST_PACK=$(echo dest.git/objects/pack/pack-*.pack) &&
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test_cmp pack-$PACK.pack $DEST_PACK &&
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# ...and wrote no loose objects
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test_stdout_line_count = 0 find dest.git/objects -type f ! -name "pack-*"
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'
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test_done
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