code: @Override
    public Long unlink(final byte[]... keys) {
      checkIsInMultiOrPipeline();
      client.unlink(keys);
      return client.getIntegerReply();
    }
docs: This command is very similar to DEL: it removes the specified keys. Just like DEL a key is
  ignored if it does not exist. However the command performs the actual memory reclaiming in a
  different thread, so it is not blocking, while DEL is. This is where the command name comes
  from: the command just unlinks the keys from the keyspace. The actual removal will happen later
  asynchronously.
  <p>
  Time complexity: O(1) for each key removed regardless of its size. Then the command does O(N)
  work in a different thread in order to reclaim memory, where N is the number of allocations the
  deleted objects where composed of.
  @param keys
  @return Integer reply: The number of keys that were unlinked