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#!/bin/sh
test_description='pack-objects breaks long cross-pack delta chains'
. ./test-lib.sh
# This mirrors a repeated push setup:
#
# 1. A client repeatedly modifies some files, makes a
# commit, and pushes the result. It does this N times
# before we get around to repacking.
#
# 2. Each push generates a thin pack with the new version of
# various objects. Let's consider some file in the root tree
# which is updated in each commit.
#
# When generating push number X, we feed commit X-1 (and
# thus blob X-1) as a preferred base. The resulting pack has
# blob X as a thin delta against blob X-1.
#
# On the receiving end, "index-pack --fix-thin" will
# complete the pack with a base copy of blob X-1.
#
# 3. In older versions of git, if we used the delta from
# pack X, then we'd always find blob X-1 as a base in the
# same pack (and generate a fresh delta).
#
# But with the pack mru, we jump from delta to delta
# following the traversal order:
#
# a. We grab blob X from pack X as a delta, putting it at
# the tip of our mru list.
#
# b. Eventually we move onto commit X-1. We need other
# objects which are only in pack X-1 (in the test code
# below, it's the containing tree). That puts pack X-1
# at the tip of our mru list.
#
# c. Eventually we look for blob X-1, and we find the
# version in pack X-1 (because it's the mru tip).
#
# Now we have blob X as a delta against X-1, which is a delta
# against X-2, and so forth.
#
# In the real world, these small pushes would get exploded by
# unpack-objects rather than "index-pack --fix-thin", but the
# same principle applies to larger pushes (they only need one
# repeatedly-modified file to generate the delta chain).
test_expect_success 'create series of packs' '
test-tool genrandom foo 4096 >content &&
prev= &&
for i in $(test_seq 1 10)
do
cat content >file &&
echo $i >>file &&
git add file &&
git commit -m $i &&
cur=$(git rev-parse HEAD^{tree}) &&
{
test -n "$prev" && echo "-$prev"
echo $cur
echo "$(git rev-parse :file) file"
} | git pack-objects --stdout >tmp &&
git index-pack --stdin --fix-thin <tmp || return 1
prev=$cur
done
'
max_chain() {
git index-pack --verify-stat-only "$1" >output &&
perl -lne '
/chain length = (\d+)/ and $len = $1;
END { print $len }
' output
}
# Note that this whole setup is pretty reliant on the current
# packing heuristics. We double-check that our test case
# actually produces a long chain. If it doesn't, it should be
# adjusted (or scrapped if the heuristics have become too unreliable)
test_expect_success 'packing produces a long delta' '
# Use --window=0 to make sure we are seeing reused deltas,
# not computing a new long chain.
pack=$(git pack-objects --all --window=0 </dev/null pack) &&
echo 9 >expect &&
max_chain pack-$pack.pack >actual &&
test_i18ncmp expect actual
'
test_expect_success '--depth limits depth' '
pack=$(git pack-objects --all --depth=5 </dev/null pack) &&
echo 5 >expect &&
max_chain pack-$pack.pack >actual &&
test_i18ncmp expect actual
'
test_done
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