t/t5316-pack-delta-depth.sh

   1 #!/bin/sh
   2
   3 test_description='pack-objects breaks long cross-pack delta chains'
   4 . ./test-lib.sh
   5
   6 # This mirrors a repeated push setup:
   7 #
   8 # 1. A client repeatedly modifies some files, makes a
   9 #      commit, and pushes the result. It does this N times
  10 #      before we get around to repacking.
  11 #
  12 # 2. Each push generates a thin pack with the new version of
  13 #    various objects. Let's consider some file in the root tree
  14 #    which is updated in each commit.
  15 #
  16 #    When generating push number X, we feed commit X-1 (and
  17 #    thus blob X-1) as a preferred base. The resulting pack has
  18 #    blob X as a thin delta against blob X-1.
  19 #
  20 #    On the receiving end, "index-pack --fix-thin" will
  21 #    complete the pack with a base copy of blob X-1.
  22 #
  23 # 3. In older versions of git, if we used the delta from
  24 #    pack X, then we'd always find blob X-1 as a base in the
  25 #    same pack (and generate a fresh delta).
  26 #
  27 #    But with the pack mru, we jump from delta to delta
  28 #    following the traversal order:
  29 #
  30 #      a. We grab blob X from pack X as a delta, putting it at
  31 #         the tip of our mru list.
  32 #
  33 #      b. Eventually we move onto commit X-1. We need other
  34 #         objects which are only in pack X-1 (in the test code
  35 #         below, it's the containing tree). That puts pack X-1
  36 #         at the tip of our mru list.
  37 #
  38 #      c. Eventually we look for blob X-1, and we find the
  39 #         version in pack X-1 (because it's the mru tip).
  40 #
  41 # Now we have blob X as a delta against X-1, which is a delta
  42 # against X-2, and so forth.
  43 #
  44 # In the real world, these small pushes would get exploded by
  45 # unpack-objects rather than "index-pack --fix-thin", but the
  46 # same principle applies to larger pushes (they only need one
  47 # repeatedly-modified file to generate the delta chain).
  48
  49 test_expect_success 'create series of packs' '
  50         test-genrandom foo 4096 >content &&
  51         prev= &&
  52         for i in $(test_seq 1 10)
  53         do
  54                 cat content >file &&
  55                 echo $i >>file &&
  56                 git add file &&
  57                 git commit -m $i &&
  58                 cur=$(git rev-parse HEAD^{tree}) &&
  59                 {
  60                         test -n "$prev" && echo "-$prev"
  61                         echo $cur
  62                         echo "$(git rev-parse :file) file"
  63                 } | git pack-objects --stdout >tmp &&
  64                 git index-pack --stdin --fix-thin <tmp || return 1
  65                 prev=$cur
  66         done
  67 '
  68
  69 max_chain() {
  70         git index-pack --verify-stat-only "$1" >output &&
  71         perl -lne '
  72           /chain length = (\d+)/ and $len = $1;
  73           END { print $len }
  74         ' output
  75 }
  76
  77 # Note that this whole setup is pretty reliant on the current
  78 # packing heuristics. We double-check that our test case
  79 # actually produces a long chain. If it doesn't, it should be
  80 # adjusted (or scrapped if the heuristics have become too unreliable)
  81 test_expect_success 'packing produces a long delta' '
  82         # Use --window=0 to make sure we are seeing reused deltas,
  83         # not computing a new long chain.
  84         pack=$(git pack-objects --all --window=0 </dev/null pack) &&
  85         echo 9 >expect &&
  86         max_chain pack-$pack.pack >actual &&
  87         test_i18ncmp expect actual
  88 '
  89
  90 test_expect_success '--depth limits depth' '
  91         pack=$(git pack-objects --all --depth=5 </dev/null pack) &&
  92         echo 5 >expect &&
  93         max_chain pack-$pack.pack >actual &&
  94         test_i18ncmp expect actual
  95 '
  96
  97 test_done