f4609b896f
This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because there is some breakage in the git build related to the netrc credentials helper which someone has taken care of in nixpkgs. The stable channel is not used for anything other than git, so this should be fine. Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb
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 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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