Thread

1. officialchicken · 1789763598 · focus · HN ↗

   [dead]

   1. cyberpunk · 1789764581 · focus · HN ↗

      Anyone have an idea how it behaves differently from google's jump hash algorithm? The cool thing about google's one is it's so short I can include it in a HN comment:

          int32_t JumpConsistentHash(uint64_t key, int32_t num_buckets) {
            int64_t b = 1, j = 0;
            while (j < num_buckets) {
              b = j;
              key = key * 2862933555777941757ULL + 1;
              j = (b + 1) * (double(1LL << 31) / double((key >> 33) + 1));
            }
            return b;
          }
      

      <a href="https:&#x2F;&#x2F;arxiv.org&#x2F;pdf&#x2F;1406.2294" rel="nofollow">https:&#x2F;&#x2F;arxiv.org&#x2F;pdf&#x2F;1406.2294

      1. prirun · 1789768586 · focus · HN ↗

         I have used Google&#x27;s jump hash. As I recall, one of the main differences is that jump hash doesn&#x27;t have a mechanism to remove targets, eg, a server dies and you don&#x27;t want to route requests to it. Traditional consistent hashing can do that. I guess if you had 4 servers, server #4 dies, then you can go back to 3 servers by just changing num_buckets from 4 to 3. But if server 1 dies, you can&#x27;t.

         Jump hash does allow adding more targets and preserves the property that most request targets stay the same when adding a new target, so if you had 3 targets and add a fourth, ~8% of the requests that would have been sent to targets 1-3 are sent to target 4, evenly chosen from servers 1-3.

Unofficial Hacker News client; not affiliated with Y Combinator.