t/t5316-pack-delta-depth.sh

   1 #!/bin/sh
   2
   3 test_description='pack-objects breaks long cross-pack delta chains'
   4
   5 TEST_PASSES_SANITIZE_LEAK=true
   6 . ./test-lib.sh
   7
   8 # This mirrors a repeated push setup:
   9 #
  10 # 1. A client repeatedly modifies some files, makes a
  11 #      commit, and pushes the result. It does this N times
  12 #      before we get around to repacking.
  13 #
  14 # 2. Each push generates a thin pack with the new version of
  15 #    various objects. Let's consider some file in the root tree
  16 #    which is updated in each commit.
  17 #
  18 #    When generating push number X, we feed commit X-1 (and
  19 #    thus blob X-1) as a preferred base. The resulting pack has
  20 #    blob X as a thin delta against blob X-1.
  21 #
  22 #    On the receiving end, "index-pack --fix-thin" will
  23 #    complete the pack with a base copy of blob X-1.
  24 #
  25 # 3. In older versions of git, if we used the delta from
  26 #    pack X, then we'd always find blob X-1 as a base in the
  27 #    same pack (and generate a fresh delta).
  28 #
  29 #    But with the pack mru, we jump from delta to delta
  30 #    following the traversal order:
  31 #
  32 #      a. We grab blob X from pack X as a delta, putting it at
  33 #         the tip of our mru list.
  34 #
  35 #      b. Eventually we move onto commit X-1. We need other
  36 #         objects which are only in pack X-1 (in the test code
  37 #         below, it's the containing tree). That puts pack X-1
  38 #         at the tip of our mru list.
  39 #
  40 #      c. Eventually we look for blob X-1, and we find the
  41 #         version in pack X-1 (because it's the mru tip).
  42 #
  43 # Now we have blob X as a delta against X-1, which is a delta
  44 # against X-2, and so forth.
  45 #
  46 # In the real world, these small pushes would get exploded by
  47 # unpack-objects rather than "index-pack --fix-thin", but the
  48 # same principle applies to larger pushes (they only need one
  49 # repeatedly-modified file to generate the delta chain).
  50
  51 test_expect_success 'create series of packs' '
  52         test-tool genrandom foo 4096 >content &&
  53         prev= &&
  54         for i in $(test_seq 1 10)
  55         do
  56                 cat content >file &&
  57                 echo $i >>file &&
  58                 git add file &&
  59                 git commit -m $i &&
  60                 cur=$(git rev-parse HEAD^{tree}) &&
  61                 {
  62                         if test -n "$prev"
  63                         then
  64                                 echo "-$prev"
  65                         fi &&
  66                         echo $cur &&
  67                         echo "$(git rev-parse :file) file"
  68                 } | git pack-objects --stdout >tmp &&
  69                 GIT_TRACE2_EVENT=$PWD/trace \
  70                 git index-pack -v --stdin --fix-thin <tmp || return 1 &&
  71                 grep -c region_enter.*progress trace >enter &&
  72                 grep -c region_leave.*progress trace >leave &&
  73                 test_cmp enter leave &&
  74                 prev=$cur
  75         done
  76 '
  77
  78 max_chain() {
  79         git index-pack --verify-stat-only "$1" >output &&
  80         perl -lne '
  81           BEGIN { $len = 0 }
  82           /chain length = (\d+)/ and $len = $1;
  83           END { print $len }
  84         ' output
  85 }
  86
  87 # Note that this whole setup is pretty reliant on the current
  88 # packing heuristics. We double-check that our test case
  89 # actually produces a long chain. If it doesn't, it should be
  90 # adjusted (or scrapped if the heuristics have become too unreliable)
  91 test_expect_success 'packing produces a long delta' '
  92         # Use --window=0 to make sure we are seeing reused deltas,
  93         # not computing a new long chain.
  94         pack=$(git pack-objects --all --window=0 </dev/null pack) &&
  95         echo 9 >expect &&
  96         max_chain pack-$pack.pack >actual &&
  97         test_cmp expect actual
  98 '
  99
 100 test_expect_success '--depth limits depth' '
 101         pack=$(git pack-objects --all --depth=5 </dev/null pack) &&
 102         echo 5 >expect &&
 103         max_chain pack-$pack.pack >actual &&
 104         test_cmp expect actual
 105 '
 106
 107 test_expect_success '--depth=0 disables deltas' '
 108         pack=$(git pack-objects --all --depth=0 </dev/null pack) &&
 109         echo 0 >expect &&
 110         max_chain pack-$pack.pack >actual &&
 111         test_cmp expect actual
 112 '
 113
 114 test_expect_success 'negative depth disables deltas' '
 115         pack=$(git pack-objects --all --depth=-1 </dev/null pack) &&
 116         echo 0 >expect &&
 117         max_chain pack-$pack.pack >actual &&
 118         test_cmp expect actual
 119 '
 120
 121 test_done