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