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runtime: raise alert threshold on window smhasher test

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This alert is triggering occasionally. I've investigated the
collisions that happen, and they all seem to be pairwise, so they are
not a big deal.  "pairwise" = when there are 32 collisions, it is two
keys mapping to the same hash, 32 times, not 33 keys all mapping to
the same hash.

Add some t.Logf calls in case this comes back, which will help isolate
the problem.

Fixes #39352

Change-Id: I1749d7c8efd0afcf9024d8964d15bc0f58a86e4f
Reviewed-on: https://go-review.googlesource.com/c/go/+/237718
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Keith Randall 2020-06-12 11:07:56 -07:00
parent 7d975ae9c0
commit 8dae5390cb
1 changed files with 5 additions and 3 deletions
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8
src/runtime/hash_test.go
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@ -152,14 +152,13 @@ func (s *HashSet) addS_seed(x string, seed uintptr) {
s.add(StringHash(x, seed)) s.add(StringHash(x, seed))
} }
func (s *HashSet) check(t *testing.T) { func (s *HashSet) check(t *testing.T) {
const SLOP = 10.0 const SLOP = 50.0
collisions := s.n - len(s.m) collisions := s.n - len(s.m)
//fmt.Printf("%d/%d\n", len(s.m), s.n)
pairs := int64(s.n) * int64(s.n-1) / 2 pairs := int64(s.n) * int64(s.n-1) / 2
expected := float64(pairs) / math.Pow(2.0, float64(hashSize)) expected := float64(pairs) / math.Pow(2.0, float64(hashSize))
stddev := math.Sqrt(expected) stddev := math.Sqrt(expected)
if float64(collisions) > expected+SLOP*(3*stddev+1) { if float64(collisions) > expected+SLOP*(3*stddev+1) {
t.Errorf("unexpected number of collisions: got=%d mean=%f stddev=%f", collisions, expected, stddev) t.Errorf("unexpected number of collisions: got=%d mean=%f stddev=%f threshold=%f", collisions, expected, stddev, expected+SLOP*(3*stddev+1))
} }
} }
@ -564,8 +563,11 @@ func avalancheTest1(t *testing.T, k Key) {
// All bit rotations of a set of distinct keys // All bit rotations of a set of distinct keys
func TestSmhasherWindowed(t *testing.T) { func TestSmhasherWindowed(t *testing.T) {
t.Logf("32 bit keys")
windowed(t, &Int32Key{}) windowed(t, &Int32Key{})
t.Logf("64 bit keys")
windowed(t, &Int64Key{}) windowed(t, &Int64Key{})
t.Logf("string keys")
windowed(t, &BytesKey{make([]byte, 128)}) windowed(t, &BytesKey{make([]byte, 128)})
} }
func windowed(t *testing.T, k Key) { func windowed(t *testing.T, k Key) {