public void testConsistentHash_probabilities() {
AtomicLongMap<Integer> map = AtomicLongMap.create();
Random r = new Random(9);
for (int i = 0; i < ITERS; i++) {
countRemaps(r.nextLong(), map);
}
for (int shard = 2; shard <= MAX_SHARDS; shard++) {
// Rough: don't exceed 1.2x the expected number of remaps by more than 20
assertTrue(map.get(shard) <= 1.2 * ITERS / shard + 20);
}
}
private void countRemaps(long h, AtomicLongMap<Integer> map) {
int last = 0;
for (int shards = 2; shards <= MAX_SHARDS; shards++) {
int chosen = Hashing.consistentHash(h, shards);
if (chosen != last) {
map.incrementAndGet(shards);
last = chosen;
}
}
}