dc_aware_policy.cpp

/*
  Copyright (c) DataStax, Inc.

  Licensed 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 "dc_aware_policy.hpp"

#include "logger.hpp"
#include "request_handler.hpp"
#include "scoped_lock.hpp"

#include <algorithm>

namespace cass {

static const CopyOnWriteHostVec NO_HOSTS(new HostVec());

void DCAwarePolicy::init(const Host::Ptr& connected_host,
                         const HostMap& hosts,
                         Random* random) {
  if (local_dc_.empty() && connected_host && !connected_host->dc().empty()) {
    LOG_INFO("Using '%s' for the local data center "
             "(if this is incorrect, please provide the correct data center)",
             connected_host->dc().c_str());
    local_dc_ = connected_host->dc();
  }

  for (HostMap::const_iterator i = hosts.begin(),
       end = hosts.end(); i != end; ++i) {
    on_add(i->second);
  }
  if (random != NULL) {
    index_ = random->next(std::max(static_cast<size_t>(1), hosts.size()));
  }
}

CassHostDistance DCAwarePolicy::distance(const Host::Ptr& host) const {
  if (local_dc_.empty() || host->dc() == local_dc_) {
    return CASS_HOST_DISTANCE_LOCAL;
  }

  const CopyOnWriteHostVec& hosts = per_remote_dc_live_hosts_.get_hosts(host->dc());
  size_t num_hosts = std::min(hosts->size(), used_hosts_per_remote_dc_);
  for (size_t i = 0; i < num_hosts; ++i) {
    if ((*hosts)[i]->address() == host->address()) {
      return CASS_HOST_DISTANCE_REMOTE;
    }
  }

  return CASS_HOST_DISTANCE_IGNORE;
}

QueryPlan* DCAwarePolicy::new_query_plan(const std::string& keyspace,
                                         RequestHandler* request_handler,
                                         const TokenMap* token_map) {
  CassConsistency cl = request_handler != NULL ? request_handler->consistency() : CASS_DEFAULT_CONSISTENCY;
  return new DCAwareQueryPlan(this, cl, index_++);
}

void DCAwarePolicy::on_add(const Host::Ptr& host) {
  const std::string& dc = host->dc();
  if (local_dc_.empty() && !dc.empty()) {
    LOG_INFO("Using '%s' for local data center "
             "(if this is incorrect, please provide the correct data center)",
             host->dc().c_str());
    local_dc_ = dc;
  }

  if (dc == local_dc_) {
    local_dc_live_hosts_->push_back(host);
  } else {
    per_remote_dc_live_hosts_.add_host_to_dc(dc, host);
  }
}

void DCAwarePolicy::on_remove(const Host::Ptr& host) {
  const std::string& dc = host->dc();
  if (dc == local_dc_) {
    remove_host(local_dc_live_hosts_, host);
  } else {
    per_remote_dc_live_hosts_.remove_host_from_dc(host->dc(), host);
  }
}

void DCAwarePolicy::on_up(const Host::Ptr& host) {
  on_add(host);
}

void DCAwarePolicy::on_down(const Host::Ptr& host) {
  on_remove(host);
}

void DCAwarePolicy::PerDCHostMap::add_host_to_dc(const std::string& dc, const Host::Ptr& host) {
  ScopedWriteLock wl(&rwlock_);
  Map::iterator i = map_.find(dc);
  if (i == map_.end()) {
    CopyOnWriteHostVec hosts(new HostVec());
    hosts->push_back(host);
    map_.insert(Map::value_type(dc, hosts));
  } else {
    add_host(i->second, host);
  }
}

void DCAwarePolicy::PerDCHostMap::remove_host_from_dc(const std::string& dc, const Host::Ptr& host) {
  ScopedWriteLock wl(&rwlock_);
  Map::iterator i = map_.find(dc);
  if (i != map_.end()) {
    remove_host(i->second, host);
  }
}

const CopyOnWriteHostVec& DCAwarePolicy::PerDCHostMap::get_hosts(const std::string& dc) const {
  ScopedReadLock rl(&rwlock_);
  Map::const_iterator i = map_.find(dc);
  if (i == map_.end()) return NO_HOSTS;
  return i->second;
}

void DCAwarePolicy::PerDCHostMap::copy_dcs(KeySet* dcs) const {
  ScopedReadLock rl(&rwlock_);
  for (Map::const_iterator i = map_.begin(),
       end = map_.end(); i != end; ++i) {
    dcs->insert(i->first);
  }
}

// Helper functions to prevent copy (Notice: "const CopyOnWriteHostVec&")

static const Host::Ptr& get_next_host(const CopyOnWriteHostVec& hosts, size_t index) {
  return (*hosts)[index % hosts->size()];
}

static const Host::Ptr& get_next_host_bounded(const CopyOnWriteHostVec& hosts,
                                              size_t index, size_t bound) {
  return (*hosts)[index % std::min(hosts->size(), bound)];
}

static size_t get_hosts_size(const CopyOnWriteHostVec& hosts) {
  return hosts->size();
}

DCAwarePolicy::DCAwareQueryPlan::DCAwareQueryPlan(const DCAwarePolicy* policy,
                                                  CassConsistency cl,
                                                  size_t start_index)
  : policy_(policy)
  , cl_(cl)
  , hosts_(policy_->local_dc_live_hosts_)
  , local_remaining_(get_hosts_size(hosts_))
  , remote_remaining_(0)
  , index_(start_index) {}

Host::Ptr DCAwarePolicy::DCAwareQueryPlan::compute_next() {
  while (local_remaining_ > 0) {
    --local_remaining_;
    const Host::Ptr& host(get_next_host(hosts_, index_++));
    if (host->is_up()) {
      return host;
    }
  }

  if (policy_->skip_remote_dcs_for_local_cl_ && is_dc_local(cl_)) {
    return Host::Ptr();
  }

  if (!remote_dcs_) {
    remote_dcs_.reset(new PerDCHostMap::KeySet());
    policy_->per_remote_dc_live_hosts_.copy_dcs(remote_dcs_.get());
  }

  while (true) {
    while (remote_remaining_ > 0) {
      --remote_remaining_;
      const Host::Ptr& host(get_next_host_bounded(hosts_,
                                                  index_++,
                                                  policy_->used_hosts_per_remote_dc_));
      if (host->is_up()) {
        return host;
      }
    }

    if (remote_dcs_->empty()) {
      break;
    }

    PerDCHostMap::KeySet::iterator i = remote_dcs_->begin();
    hosts_ = policy_->per_remote_dc_live_hosts_.get_hosts(*i);
    remote_remaining_ = std::min(get_hosts_size(hosts_), policy_->used_hosts_per_remote_dc_);
    remote_dcs_->erase(i);
  }

  return Host::Ptr();
}

} // namespace cass