src/latency_aware_policy.cpp

/*
  Licensed to the Apache Software Foundation (ASF) under one
  or more contributor license agreements.  See the NOTICE file
  distributed with this work for additional information
  regarding copyright ownership.  The ASF licenses this file
  to you under the Apache License, Version 2.0 (the
  "License"); you may not use this file except in compliance
  with the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

#include "latency_aware_policy.hpp"

#include "get_time.hpp"
#include "logger.hpp"

#include <algorithm>
#include <iterator>

using namespace datastax;
using namespace datastax::internal;
using namespace datastax::internal::core;

void LatencyAwarePolicy::init(const Host::Ptr& connected_host, const HostMap& hosts, Random* random,
                              const String& local_dc) {
  hosts_->reserve(hosts.size());
  std::transform(hosts.begin(), hosts.end(), std::back_inserter(*hosts_), GetHost());
  for (HostMap::const_iterator i = hosts.begin(), end = hosts.end(); i != end; ++i) {
    i->second->enable_latency_tracking(settings_.scale_ns, settings_.min_measured);
  }
  ChainedLoadBalancingPolicy::init(connected_host, hosts, random, local_dc);
}

void LatencyAwarePolicy::register_handles(uv_loop_t* loop) { start_timer(loop); }

void LatencyAwarePolicy::close_handles() { timer_.stop(); }

QueryPlan* LatencyAwarePolicy::new_query_plan(const String& keyspace,
                                              RequestHandler* request_handler,
                                              const TokenMap* token_map) {
  return new LatencyAwareQueryPlan(
      this, child_policy_->new_query_plan(keyspace, request_handler, token_map));
}

void LatencyAwarePolicy::on_host_added(const Host::Ptr& host) {
  host->enable_latency_tracking(settings_.scale_ns, settings_.min_measured);
  add_host(hosts_, host);
  ChainedLoadBalancingPolicy::on_host_added(host);
}

void LatencyAwarePolicy::on_host_removed(const Host::Ptr& host) {
  remove_host(hosts_, host);
  ChainedLoadBalancingPolicy::on_host_removed(host);
}

void LatencyAwarePolicy::start_timer(uv_loop_t* loop) {
  timer_.start(loop, settings_.update_rate_ms, bind_callback(&LatencyAwarePolicy::on_timer, this));
}

void LatencyAwarePolicy::on_timer(Timer* timer) {
  const CopyOnWriteHostVec& hosts(hosts_);

  int64_t new_min_average = CASS_INT64_MAX;
  int64_t now = uv_hrtime();

  for (HostVec::const_iterator i = hosts->begin(), end = hosts->end(); i != end; ++i) {
    TimestampedAverage latency = (*i)->get_current_average();
    if (latency.average >= 0 && latency.num_measured >= settings_.min_measured &&
        (now - latency.timestamp) <= settings_.retry_period_ns) {
      new_min_average = std::min(new_min_average, latency.average);
    }
  }

  if (new_min_average != CASS_INT64_MAX) {
    LOG_TRACE("Calculated new minimum: %f", static_cast<double>(new_min_average) / 1e6);
    min_average_.store(new_min_average);
  }

  start_timer(timer_.loop());
}

Host::Ptr LatencyAwarePolicy::LatencyAwareQueryPlan::compute_next() {
  int64_t min = policy_->min_average_.load();
  const Settings& settings = policy_->settings_;
  uint64_t now = uv_hrtime();

  Host::Ptr host;
  while ((host = child_plan_->compute_next())) {
    TimestampedAverage latency = host->get_current_average();

    if (min < 0 || latency.average < 0 || latency.num_measured < settings.min_measured ||
        (now - latency.timestamp) > settings.retry_period_ns) {
      return host;
    }

    if (latency.average <= static_cast<int64_t>(settings.exclusion_threshold * min)) {
      return host;
    }

    LOG_TRACE("Skipping %s because latency is too high %f", host->address_string().c_str(),
              static_cast<double>(latency.average) / 1e6);
    skipped_.push_back(host);
  }

  if (skipped_index_ < skipped_.size()) {
    return skipped_[skipped_index_++];
  }

  return Host::Ptr();
}