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arangodb/arangod/Agency/Agent.cpp

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////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// 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.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Kaveh Vahedipour
////////////////////////////////////////////////////////////////////////////////
#include "Agent.h"
#include "Basics/ConditionLocker.h"
#include "RestServer/DatabaseFeature.h"
#include "RestServer/QueryRegistryFeature.h"
#include "VocBase/server.h"
#include "VocBase/vocbase.h"
#include <velocypack/Iterator.h>
#include <velocypack/velocypack-aliases.h>
#include <chrono>
using namespace arangodb::application_features;
using namespace arangodb::velocypack;
namespace arangodb {
namespace consensus {
/// Agent configuration
Agent::Agent(config_t const& config)
: Thread("Agent"),
_config(config),
_lastCommitIndex(0),
_spearhead(this),
_readDB(this),
_nextCompationAfter(_config.compactionStepSize) {
_state.configure(this);
_constituent.configure(this);
_confirmed.resize(size(), 0); // agency's size and reset to 0
}
/// This agent's id
arangodb::consensus::id_t Agent::id() const {
return _config.id;
}
/// Dtor shuts down thread
Agent::~Agent() {
shutdown();
}
/// State machine
State const& Agent::state() const {
return _state;
}
/// Start all agent thread
bool Agent::start() {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Starting agency comm worker.";
Thread::start();
return true;
}
/// This agent's term
term_t Agent::term() const {
return _constituent.term();
}
/// Agency size
size_t Agent::size() const {
return _config.size();
}
/// My endpoint
std::string const& Agent::endpoint() const {
return _config.endpoint;
}
/// Handle voting
priv_rpc_ret_t Agent::requestVote(
term_t t, arangodb::consensus::id_t id, index_t lastLogIndex,
index_t lastLogTerm, query_t const& query) {
/// Are we receiving new endpoints
if (query != nullptr) { // record new endpoints
if (query->slice().hasKey("endpoints") &&
query->slice().get("endpoints").isArray()) {
size_t j = 0;
for (auto const& i : VPackArrayIterator(query->slice().get("endpoints"))) {
_config.endpoints[j++] = i.copyString();
}
}
}
/// Constituent handles this
return priv_rpc_ret_t(_constituent.vote(t, id, lastLogIndex, lastLogTerm),
this->term());
}
/// Get configuration
config_t const& Agent::config() const {
return _config;
}
/// Leader's id
arangodb::consensus::id_t Agent::leaderID() const {
return _constituent.leaderID();
}
/// Are we leading?
bool Agent::leading() const {
return _constituent.leading();
}
// Waits here for confirmation of log's commits up to index.
// Timeout in seconds
bool Agent::waitFor(index_t index, double timeout) {
if (size() == 1) { // single host agency
return true;
}
CONDITION_LOCKER(guard, _waitForCV);
// Wait until woken up through AgentCallback
while (true) {
/// success?
if (_lastCommitIndex >= index) {
return true;
}
// timeout
if (!_waitForCV.wait(static_cast<uint64_t>(1.0e6 * timeout))) {
return false;
}
// shutting down
if (this->isStopping()) {
return false;
}
}
// We should never get here
TRI_ASSERT(false);
}
// AgentCallback reports id of follower and its highest processed index
void Agent::reportIn(arangodb::consensus::id_t id, index_t index) {
MUTEX_LOCKER(mutexLocker, _ioLock);
TRI_ASSERT(id<_confirmed.size());
if (index > _confirmed[id]) { // progress this follower?
_confirmed[id] = index;
}
if (index > _lastCommitIndex) { // progress last commit?
size_t n = 0;
for (size_t i = 0; i < size(); ++i) {
n += (_confirmed[i] >= index);
}
// catch up read database and commit index
if (n > size() / 2) {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Critical mass for commiting "
<< _lastCommitIndex + 1 << " through "
<< index << " to read db";
_readDB.apply(_state.slices(_lastCommitIndex + 1, index));
_lastCommitIndex = index;
if (_lastCommitIndex >= _nextCompationAfter) {
_state.compact(_lastCommitIndex);
_nextCompationAfter += _config.compactionStepSize;
}
}
}
{
CONDITION_LOCKER(guard, _waitForCV);
guard.broadcast();
}
}
/// Followers' append entries
bool Agent::recvAppendEntriesRPC(term_t term,
arangodb::consensus::id_t leaderId,
index_t prevIndex, term_t prevTerm,
index_t leaderCommitIndex,
query_t const& queries) {
// Update commit index
if (queries->slice().type() != VPackValueType::Array) {
LOG_TOPIC(WARN, Logger::AGENCY)
<< "Received malformed entries for appending. Discarting!";
return false;
}
MUTEX_LOCKER(mutexLocker, _ioLock);
// index_t lastPersistedIndex = _lastCommitIndex;
if (this->term() > term) {
LOG_TOPIC(WARN, Logger::AGENCY) << "I have a higher term than RPC caller.";
return false;
}
if (!_constituent.vote(term, leaderId, prevIndex, prevTerm, true)) {
return false;
}
_state.removeConflicts(queries);
if (queries->slice().length()) {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Appending "
<< queries->slice().length()
<< " entries to state machine.";
/* bool success = */
_state.log(queries, term, prevIndex, prevTerm);
_spearhead.apply(_state.slices(_lastCommitIndex + 1, leaderCommitIndex));
_readDB.apply(_state.slices(_lastCommitIndex + 1, leaderCommitIndex));
_lastCommitIndex = leaderCommitIndex;
}
if (_lastCommitIndex >= _nextCompationAfter) {
_state.compact(_lastCommitIndex);
_nextCompationAfter += _config.compactionStepSize;
}
return true;
}
/// Leader's append entries
priv_rpc_ret_t Agent::sendAppendEntriesRPC(
arangodb::consensus::id_t follower_id) {
index_t last_confirmed = _confirmed[follower_id];
std::vector<log_t> unconfirmed = _state.get(last_confirmed);
term_t t(0);
{
MUTEX_LOCKER(mutexLocker, _ioLock);
t = this->term();
}
if (unconfirmed.empty()) {
return priv_rpc_ret_t(false, t);
}
// RPC path
std::stringstream path;
path << "/_api/agency_priv/appendEntries?term=" << t << "&leaderId=" << id()
<< "&prevLogIndex=" << unconfirmed.front().index
<< "&prevLogTerm=" << unconfirmed.front().term
<< "&leaderCommit=" << _lastCommitIndex;
// Headers
auto headerFields =
std::make_unique<std::unordered_map<std::string, std::string>>();
// Highest unconfirmed
index_t last = unconfirmed[0].index;
// Body
Builder builder;
builder.add(VPackValue(VPackValueType::Array));
for (size_t i = 1; i < unconfirmed.size(); ++i) {
auto const& entry = unconfirmed.at(i);
builder.add(VPackValue(VPackValueType::Object));
builder.add("index", VPackValue(entry.index));
builder.add("term", VPackValue(entry.term));
builder.add("query", VPackSlice(entry.entry->data()));
builder.close();
last = entry.index;
}
builder.close();
// Verbose output
if (unconfirmed.size() > 1) {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Appending " << unconfirmed.size() - 1
<< " entries up to index " << last
<< " to follower " << follower_id;
}
// Send request
arangodb::ClusterComm::instance()->asyncRequest(
"1", 1, _config.endpoints[follower_id],
arangodb::GeneralRequest::RequestType::POST, path.str(),
std::make_shared<std::string>(builder.toJson()), headerFields,
std::make_shared<AgentCallback>(this, follower_id, last), 1, true);
return priv_rpc_ret_t(true, t);
}
/// Load persistent state
bool Agent::load() {
DatabaseFeature* database =
ApplicationServer::getFeature<DatabaseFeature>("Database");
auto vocbase = database->vocbase();
if (vocbase == nullptr) {
LOG_TOPIC(FATAL, Logger::AGENCY) << "could not determine _system database";
FATAL_ERROR_EXIT();
}
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Loading persistent state.";
if (!_state.loadCollections(vocbase, _config.waitForSync)) {
LOG_TOPIC(DEBUG, Logger::AGENCY)
<< "Failed to load persistent state on startup.";
}
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Reassembling spearhead and read stores.";
_spearhead.apply(_state.slices(_lastCommitIndex + 1));
reportIn(id(), _state.lastLog().index);
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Starting spearhead worker.";
_spearhead.start();
_readDB.start();
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Starting constituent personality.";
auto queryRegistry = QueryRegistryFeature::QUERY_REGISTRY;
TRI_ASSERT(queryRegistry != nullptr);
_constituent.start(vocbase, queryRegistry);
if (_config.supervision) {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Starting cluster sanity facilities";
_supervision.start(this);
}
return true;
}
/// Write new entries to replicated state and store
write_ret_t Agent::write(query_t const& query) {
std::vector<bool> applied;
std::vector<index_t> indices;
index_t maxind = 0;
// Only leader else redirect
if (!_constituent.leading()) {
return write_ret_t(false, _constituent.leaderID());
}
// Apply to spearhead and get indices for log entries
{
MUTEX_LOCKER(mutexLocker, _ioLock);
applied = _spearhead.apply(query);
indices = _state.log(query, applied, term());
}
// Maximum log index
if (!indices.empty()) {
maxind = *std::max_element(indices.begin(), indices.end());
}
// Report that leader has persisted
reportIn(id(), maxind);
return write_ret_t(true, id(), applied, indices);
}
/// Read from store
read_ret_t Agent::read(query_t const& query) {
// Only leader else redirect
if (!_constituent.leading()) {
return read_ret_t(false, _constituent.leaderID());
}
// Retrieve data from readDB
query_t result = std::make_shared<arangodb::velocypack::Builder>();
std::vector<bool> success = _readDB.read(query, result);
return read_ret_t(true, _constituent.leaderID(), success, result);
}
/// Send out append entries to followers regularly or on event
void Agent::run() {
CONDITION_LOCKER(guard, _appendCV);
// Only run in case we are in multi-host mode
while (!this->isStopping() && size() > 1) {
if (leading()) { // Only if leading
_appendCV.wait(100000);
} else {
_appendCV.wait(); // Else wait for our moment in the sun
}
// Append entries to followers
for (arangodb::consensus::id_t i = 0; i < size(); ++i) {
if (i != id()) {
sendAppendEntriesRPC(i);
}
}
}
}
/// Orderly shutdown
void Agent::beginShutdown() {
Thread::beginShutdown();
// Stop supervision
if (_config.supervision) {
_supervision.beginShutdown();
}
// Stop constituent and key value stores
_constituent.beginShutdown();
_spearhead.beginShutdown();
_readDB.beginShutdown();
// Wake up all waiting rest handlers
{
CONDITION_LOCKER(guardW, _waitForCV);
guardW.broadcast();
}
// Wake up run
{
CONDITION_LOCKER(guardA, _appendCV);
guardA.broadcast();
}
}
/// Becoming leader
bool Agent::lead() {
// Key value stores
//rebuildDBs();
// Wake up run
CONDITION_LOCKER(guard, _appendCV);
guard.broadcast();
return true;
}
// Rebuild key value stores
bool Agent::rebuildDBs() {
MUTEX_LOCKER(mutexLocker, _ioLock);
_spearhead.apply(_state.slices());
_readDB.apply(_state.slices());
return true;
}
/// Last commit index
arangodb::consensus::index_t Agent::lastCommited() const {
return _lastCommitIndex;
}
/// Last log entry
log_t const& Agent::lastLog() const { return _state.lastLog(); }
/// Get spearhead
Store const& Agent::spearhead() const { return _spearhead; }
/// Get readdb
Store const& Agent::readDB() const { return _readDB; }
/// Rebuild from persisted state
Agent& Agent::operator=(VPackSlice const& compaction) {
// Catch up with compacted state
MUTEX_LOCKER(mutexLocker, _ioLock);
_spearhead = compaction.get("readDB");
_readDB = compaction.get("readDB");
// Catch up with commit
try {
_lastCommitIndex = std::stoul(compaction.get("_key").copyString());
} catch (std::exception const& e) {
LOG_TOPIC(ERR, Logger::AGENCY) << e.what() << " " <<__FILE__ << __LINE__;
}
// Schedule next compaction
_nextCompationAfter = _lastCommitIndex + _config.compactionStepSize;
return *this;
}
}} // namespace
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