112 lines
3.8 KiB
Bash
Executable file
112 lines
3.8 KiB
Bash
Executable file
#!/bin/sh
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test_description='test handling of inter-pack delta cycles during repack
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The goal here is to create a situation where we have two blobs, A and B, with A
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as a delta against B in one pack, and vice versa in the other. Then if we can
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persuade a full repack to find A from one pack and B from the other, that will
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give us a cycle when we attempt to reuse those deltas.
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The trick is in the "persuade" step, as it depends on the internals of how
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pack-objects picks which pack to reuse the deltas from. But we can assume
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that it does so in one of two general strategies:
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1. Using a static ordering of packs. In this case, no inter-pack cycles can
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happen. Any objects with a delta relationship must be present in the same
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pack (i.e., no "--thin" packs on disk), so we will find all related objects
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from that pack. So assuming there are no cycles within a single pack (and
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we avoid generating them via pack-objects or importing them via
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index-pack), then our result will have no cycles.
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So this case should pass the tests no matter how we arrange things.
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2. Picking the next pack to examine based on locality (i.e., where we found
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something else recently).
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In this case, we want to make sure that we find the delta versions of A and
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B and not their base versions. We can do this by putting two blobs in each
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pack. The first is a "dummy" blob that can only be found in the pack in
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question. And then the second is the actual delta we want to find.
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The two blobs must be present in the same tree, not present in other trees,
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and the dummy pathname must sort before the delta path.
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The setup below focuses on case 2. We have two commits HEAD and HEAD^, each
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which has two files: "dummy" and "file". Then we can make two packs which
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contain:
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[pack one]
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HEAD:dummy
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HEAD:file (as delta against HEAD^:file)
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HEAD^:file (as base)
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[pack two]
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HEAD^:dummy
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HEAD^:file (as delta against HEAD:file)
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HEAD:file (as base)
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Then no matter which order we start looking at the packs in, we know that we
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will always find a delta for "file", because its lookup will always come
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immediately after the lookup for "dummy".
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'
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. ./test-lib.sh
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# Create a pack containing the the tree $1 and blob $1:file, with
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# the latter stored as a delta against $2:file.
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#
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# We convince pack-objects to make the delta in the direction of our choosing
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# by marking $2 as a preferred-base edge. That results in $1:file as a thin
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# delta, and index-pack completes it by adding $2:file as a base.
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#
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# Note that the two variants of "file" must be similar enough to convince git
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# to create the delta.
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make_pack () {
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{
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printf '%s\n' "-$(git rev-parse $2)"
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printf '%s dummy\n' "$(git rev-parse $1:dummy)"
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printf '%s file\n' "$(git rev-parse $1:file)"
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} |
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git pack-objects --stdout |
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git index-pack --stdin --fix-thin
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}
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test_expect_success 'setup' '
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test-tool genrandom base 4096 >base &&
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for i in one two
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do
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# we want shared content here to encourage deltas...
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cp base file &&
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echo $i >>file &&
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# ...whereas dummy should be short, because we do not want
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# deltas that would create duplicates when we --fix-thin
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echo $i >dummy &&
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git add file dummy &&
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test_tick &&
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git commit -m $i ||
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return 1
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done &&
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make_pack HEAD^ HEAD &&
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make_pack HEAD HEAD^
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'
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test_expect_success 'repack' '
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# We first want to check that we do not have any internal errors,
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# and also that we do not hit the last-ditch cycle-breaking code
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# in write_object(), which will issue a warning to stderr.
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git repack -ad 2>stderr &&
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test_must_be_empty stderr &&
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# And then double-check that the resulting pack is usable (i.e.,
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# we did not fail to notice any cycles). We know we are accessing
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# the objects via the new pack here, because "repack -d" will have
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# removed the others.
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git cat-file blob HEAD:file >/dev/null &&
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git cat-file blob HEAD^:file >/dev/null
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'
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test_done
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