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fix(v2): use better seed for shard placement #3924

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Merged
merged 2 commits into from
Feb 19, 2025
Merged

fix(v2): use better seed for shard placement #3924

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fad1074
fix(v2): use better seed for shard placement
kolesnikovae Feb 18, 2025
5900bb2
fix(v2): update tests
kolesnikovae Feb 18, 2025
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16 changes: 11 additions & 5 deletions pkg/experiment/distributor/distributor.go
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Original file line number Diff line number Diff line change
Expand Up @@ -326,14 +326,20 @@ func (p *perm) resize(n int) {
}
}

// The value is a random generated with a crypto/rand.Read,
// and decoded as a little-endian uint64. No fancy math here.
const randSeed = 4349576827832984783

var steps [4 << 10]uint32

func init() {
r := rand.New(rand.NewSource(randSeed))
// The seed impacts mapping of shards to nodes.
// TODO(kolesnikovae):
// Stochastic approach does not work well
// in all the cases; it should be replaced
// with a deterministic one.
const randSeed = -3035313949336265834
setSeed(randSeed)
}

func setSeed(n int64) {
r := rand.New(rand.NewSource(n))
for i := range steps {
steps[i] = uint32(r.Intn(i + 1))
}
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49 changes: 24 additions & 25 deletions pkg/experiment/distributor/distributor_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -160,7 +160,7 @@ func Test_Distributor_Distribute(t *testing.T) {
// 0 1 2 3 4 5 6 7 8 9 10 11 all shards
// * * * * > * * * tenant (size 8, offset 8)
// > * * * dataset (size 4, offset 6+8 mod 12 = 2)
// a a a b b b c c a b c c shuffling (see d.distribution.shards)
// 2 1 0 1 1 2 2 0 1 0 0 2 shuffling (see d.distribution.shards)
// ----------------------------------------------------------------------
// 0 1 2 3 4 PickShard 0 (offset within dataset)
// ^ borrowed from the tenant
Expand All @@ -170,13 +170,13 @@ func Test_Distributor_Distribute(t *testing.T) {
// 1 2 3 0 4 PickShard 3

// Identical keys have identical placement.
assert.Equal(t, []string{"a", "b", "a", "b", "c"}, collect(0, 5))
assert.Equal(t, []string{"a", "b", "a", "b", "c"}, collect(0, 5))
assert.Equal(t, []string{"a", "b", "b", "a", "a"}, collect(0, 5))
assert.Equal(t, []string{"a", "b", "b", "a", "a"}, collect(0, 5))

// Placement of different keys in the dataset is bound.
assert.Equal(t, []string{"b", "a", "b", "a", "c"}, collect(1, 5))
assert.Equal(t, []string{"a", "b", "a", "b", "c"}, collect(2, 5))
assert.Equal(t, []string{"b", "a", "b", "a", "c"}, collect(3, 5))
assert.Equal(t, []string{"b", "b", "a", "a", "a"}, collect(1, 5))
assert.Equal(t, []string{"b", "a", "a", "b", "a"}, collect(2, 5))
assert.Equal(t, []string{"a", "a", "b", "b", "a"}, collect(3, 5))

// Now we're trying to collect more instances than available.
// 0 1 2 3 4 5 6 7 8 9 10 11 all shards
Expand All @@ -186,8 +186,8 @@ func Test_Distributor_Distribute(t *testing.T) {
// 6 7 2 3 8 9 10 11 0 1 4 5
// ^ ^ ^ ^ borrowed from the tenant
// ^ ^ ^ ^ borrowed from the top ring
// a a a b b b c c a b c c shuffling (see d.distribution.shards)
assert.Equal(t, []string{"a", "b", "a", "b", "c", "c", "a", "a", "b", "b", "c", "c"}, collect(2, 13))
// 2 1 0 1 1 2 2 0 1 0 0 2 shuffling (see d.distribution.shards)
assert.Equal(t, []string{"b", "a", "a", "b", "a", "c", "c", "b", "b", "c", "c", "a"}, collect(2, 13))
}

func Test_distribution_iterator(t *testing.T) {
Expand Down Expand Up @@ -419,25 +419,24 @@ func Test_permutation(t *testing.T) {
p.resize(i)
actual = append(actual, copyP(p.v))
}

expected := [][]uint32{
{},
{2, 3, 1, 0},
{2, 3, 1, 5, 6, 4, 7, 0},
{2, 3, 1, 5, 6, 4, 9, 11, 0, 7, 8, 10},
{2, 3, 1, 5, 12, 4, 14, 11, 15, 7, 8, 13, 6, 10, 9, 0},
{2, 3, 18, 5, 12, 4, 14, 11, 15, 7, 8, 13, 6, 10, 9, 19, 17, 16, 1, 0},
{2, 3, 18, 5, 12, 4, 14, 11, 15, 22, 8, 13, 6, 10, 9, 19, 17, 21, 1, 20, 0, 16, 23, 7},
{2, 3, 18, 5, 12, 4, 14, 11, 15, 22, 8, 13, 6, 27, 9, 19, 24, 21, 1, 20, 0, 16, 23, 26, 17, 10, 7, 25},
{28, 3, 18, 5, 12, 29, 14, 11, 15, 22, 8, 13, 31, 27, 9, 19, 24, 21, 1, 20, 0, 16, 23, 26, 30, 10, 7, 25, 2, 4, 17, 6},
{28, 3, 18, 5, 12, 29, 14, 11, 15, 22, 8, 13, 31, 27, 9, 19, 24, 21, 1, 20, 0, 16, 23, 26, 30, 10, 7, 25, 2, 4, 17, 6},
{2, 3, 18, 5, 12, 4, 14, 11, 15, 22, 8, 13, 6, 27, 9, 19, 24, 21, 1, 20, 0, 16, 23, 26, 17, 10, 7, 25},
{2, 3, 18, 5, 12, 4, 14, 11, 15, 22, 8, 13, 6, 10, 9, 19, 17, 21, 1, 20, 0, 16, 23, 7},
{2, 3, 18, 5, 12, 4, 14, 11, 15, 7, 8, 13, 6, 10, 9, 19, 17, 16, 1, 0},
{2, 3, 1, 5, 12, 4, 14, 11, 15, 7, 8, 13, 6, 10, 9, 0},
{2, 3, 1, 5, 6, 4, 9, 11, 0, 7, 8, 10},
{2, 3, 1, 5, 6, 4, 7, 0},
{2, 3, 1, 0},
{3, 1, 0, 2},
{3, 6, 0, 5, 7, 4, 1, 2},
{11, 6, 0, 5, 7, 8, 9, 2, 4, 1, 3, 10},
{11, 6, 0, 5, 14, 8, 15, 2, 12, 1, 3, 13, 4, 10, 7, 9},
{11, 6, 0, 19, 14, 8, 15, 2, 12, 17, 3, 18, 4, 16, 7, 9, 10, 1, 13, 5},
{11, 6, 0, 19, 14, 8, 15, 2, 21, 17, 3, 18, 4, 16, 7, 22, 10, 1, 23, 5, 9, 12, 20, 13},
{11, 6, 0, 19, 14, 8, 15, 2, 26, 17, 25, 18, 24, 16, 7, 22, 10, 1, 23, 5, 9, 12, 20, 13, 4, 3, 27, 21},
{11, 6, 0, 28, 31, 8, 15, 2, 26, 17, 25, 18, 24, 16, 7, 22, 10, 1, 23, 5, 30, 12, 20, 13, 4, 29, 27, 21, 19, 3, 9, 14},
{11, 6, 0, 28, 31, 8, 15, 2, 26, 17, 25, 18, 24, 16, 7, 22, 10, 1, 23, 5, 30, 12, 20, 13, 4, 29, 27, 21, 19, 3, 9, 14},
{11, 6, 0, 19, 14, 8, 15, 2, 26, 17, 25, 18, 24, 16, 7, 22, 10, 1, 23, 5, 9, 12, 20, 13, 4, 3, 27, 21},
{11, 6, 0, 19, 14, 8, 15, 2, 21, 17, 3, 18, 4, 16, 7, 22, 10, 1, 23, 5, 9, 12, 20, 13},
{11, 6, 0, 19, 14, 8, 15, 2, 12, 17, 3, 18, 4, 16, 7, 9, 10, 1, 13, 5},
{11, 6, 0, 5, 14, 8, 15, 2, 12, 1, 3, 13, 4, 10, 7, 9},
{11, 6, 0, 5, 7, 8, 9, 2, 4, 1, 3, 10},
{3, 6, 0, 5, 7, 4, 1, 2},
{3, 1, 0, 2},
{},
}

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