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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 "GossipCallback.h"
#include "Basics/ConditionLocker.h"
#include "RestServer/DatabaseFeature.h"
#include "RestServer/QueryRegistryFeature.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;
using namespace std::chrono;
namespace arangodb {
namespace consensus {
/// Agent configuration
Agent::Agent(config_t const& config)
: Thread("Agent"),
_config(config),
_lastCommitIndex(0),
_spearhead(this),
_readDB(this),
_serveActiveAgent(false),
_nextCompationAfter(_config.compactionStepSize()),
_inception(std::make_unique<Inception>(this)),
_activator(nullptr) {
_state.configure(this);
_constituent.configure(this);
}
/// This agent's id
std::string Agent::id() const { return config().id(); }
/// Agent's id is set once from state machine
bool Agent::id(std::string const& id) {
bool success;
if ((success = _config.setId(id))) {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "My id is " << id;
} else {
LOG_TOPIC(ERR, Logger::AGENCY) << "Cannot reassign id once set: My id is "
<< _config.id() << " reassignment to " << id;
}
return success;
}
/// Merge command line and persisted comfigurations
bool Agent::mergeConfiguration(VPackSlice const& persisted) {
return _config.merge(persisted);
}
/// Dtor shuts down thread
Agent::~Agent() {
int counter = 0;
while (_constituent.isRunning()) {
usleep(100000);
// emit warning after 5 seconds
if (++counter == 10 * 5) {
LOG_TOPIC(FATAL, Logger::AGENCY) << "constituent thread did not finish";
FATAL_ERROR_EXIT();
}
}
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;
}
/// Get all logs from state machine
query_t Agent::allLogs() const {
return _state.allLogs();
}
/// 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 Agent::endpoint() const { return _config.endpoint(); }
/// Handle voting
priv_rpc_ret_t Agent::requestVote(term_t t, std::string const& id,
index_t lastLogIndex, index_t lastLogTerm,
query_t const& query) {
return priv_rpc_ret_t(_constituent.vote(t, id, lastLogIndex, lastLogTerm),
this->term());
}
/// Get copy of momentary configuration
config_t const Agent::config() const { return _config; }
/// Leader's id
std::string Agent::leaderID() const { return _constituent.leaderID(); }
/// Are we leading?
bool Agent::leading() const { return _constituent.leading(); }
/// Start constituent personality
void Agent::startConstituent() {
activateAgency();
}
// 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(std::string const& id, index_t index) {
MUTEX_LOCKER(mutexLocker, _ioLock);
_lastAcked[id] = system_clock::now();
if (index > _confirmed[id]) { // progress this follower?
_confirmed[id] = index;
}
if (index > _lastCommitIndex) { // progress last commit?
size_t n = 0;
for (auto const& i : _config.active()) {
n += (_confirmed[i] >= index);
}
// catch up read database and commit index
if (n > size() / 2) {
LOG_TOPIC(TRACE, 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, std::string const& 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);
if (this->term() > term) { // peer at higher term
if (leaderCommitIndex >= _lastCommitIndex) { //
_constituent.follow(term);
} else {
LOG_TOPIC(WARN, Logger::AGENCY)
<< "I have a higher term than RPC caller.";
return false;
}
}
if (!_constituent.vote(term, leaderId, prevIndex, prevTerm, true)) {
LOG_TOPIC(WARN, Logger::AGENCY) << "Not voting for " << leaderId;
return false;
}
size_t nqs = queries->slice().length();
if (nqs > 0) {
size_t ndups = _state.removeConflicts(queries);
if (nqs > ndups) {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Appending " << nqs - ndups
<< " entries to state machine." << nqs
<< " " << ndups;
try {
_state.log(queries, ndups);
} catch (std::exception const& e) {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Malformed query: " << __FILE__
<< __LINE__;
}
}
}
_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
void Agent::sendAppendEntriesRPC() {
for (auto const& followerId : _config.active()) {
if (followerId != id()) {
term_t t(0);
{
MUTEX_LOCKER(mutexLocker, _ioLock);
t = this->term();
}
index_t last_confirmed = _confirmed[followerId];
std::vector<log_t> unconfirmed = _state.get(last_confirmed);
index_t highest = unconfirmed.back().index;
duration<double> m =
system_clock::now() - _lastSent[followerId];
if (highest == _lastHighest[followerId]
&& 0.5 * _config.minPing() > m.count()) {
continue;
}
// RPC path
std::stringstream path;
path << "/_api/agency_priv/appendEntries?term=" << t
<< "&leaderId=" << id()
<< "&prevLogIndex=" << unconfirmed.front().index
<< "&prevLogTerm=" << unconfirmed.front().term
<< "&leaderCommit=" << _lastCommitIndex;
// 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();
highest = entry.index;
}
builder.close();
// Verbose output
if (unconfirmed.size() > 1) {
LOG_TOPIC(DEBUG, Logger::AGENCY)
<< "Appending " << unconfirmed.size() - 1 << " entries up to index "
<< highest << " to follower " << followerId;
}
// Send request
auto headerFields =
std::make_unique<std::unordered_map<std::string, std::string>>();
arangodb::ClusterComm::instance()->asyncRequest(
"1", 1, _config.poolAt(followerId),
arangodb::rest::RequestType::POST, path.str(),
std::make_shared<std::string>(builder.toJson()), headerFields,
std::make_shared<AgentCallback>(this, followerId, highest),
0.1 * _config.minPing(), true, 0.05 * _config.minPing());
{
MUTEX_LOCKER(mutexLocker, _ioLock);
_lastSent[followerId] = system_clock::now();
_lastHighest[followerId] = highest;
}
}
}
}
/// @brief
bool Agent::activateAgency() {
if (_config.activeEmpty()) {
size_t count = 0;
for (auto const& pair : _config.pool()) {
_config.activePushBack(pair.first);
if (++count == size()) {
break;
}
}
bool persisted = false;
try {
persisted = _state.persistActiveAgents(_config.activeToBuilder(),
_config.poolToBuilder());
} catch (std::exception const& e) {
LOG_TOPIC(FATAL, Logger::AGENCY) << "Failed to persist active agency: "
<< e.what();
}
return persisted;
}
return true;
}
/// Load persistent state
bool Agent::load() {
DatabaseFeature* database =
ApplicationServer::getFeature<DatabaseFeature>("Database");
auto vocbase = database->systemDatabase();
auto queryRegistry = QueryRegistryFeature::QUERY_REGISTRY;
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, queryRegistry, _config.waitForSync())) {
LOG_TOPIC(DEBUG, Logger::AGENCY)
<< "Failed to load persistent state on startup.";
}
if (size() > 1) {
_inception->start();
}
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Reassembling spearhead and read stores.";
_spearhead.apply(_state.slices(_lastCommitIndex + 1));
{
CONDITION_LOCKER(guard, _appendCV);
guard.broadcast();
}
reportIn(id(), _state.lastLog().index);
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Starting spearhead worker.";
if (!this->isStopping()) {
_spearhead.start();
_readDB.start();
}
TRI_ASSERT(queryRegistry != nullptr);
if (size() == 1) {
activateAgency();
}
if (!this->isStopping()) {
_constituent.start(vocbase, queryRegistry);
}
if (!this->isStopping() && _config.supervision()) {
LOG_TOPIC(DEBUG, Logger::AGENCY) << "Starting cluster sanity facilities";
_supervision.start(this);
}
return true;
}
/// Challenge my own leadership
bool Agent::challengeLeadership() {
// Still leading?
size_t good = 0;
for (auto const& i : _lastAcked) {
duration<double> m =
system_clock::now() - i.second;
if (0.9 * _config.minPing() > m.count()) {
++good;
}
}
return (good < size() / 2); // not counting myself
}
/// 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());
} else {
if (challengeLeadership()) {
_constituent.candidate();
return write_ret_t(false, NO_LEADER);
}
}
// 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) {
MUTEX_LOCKER(mutexLocker, _ioLock);
// Only leader else redirect
if (!_constituent.leading()) {
return read_ret_t(false, _constituent.leaderID());
} else {
if (challengeLeadership()) {
_constituent.candidate();
return read_ret_t(false, NO_LEADER);
}
}
// Retrieve data from readDB
auto 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);
using namespace std::chrono;
auto tp = system_clock::now();
// Only run in case we are in multi-host mode
while (!this->isStopping() && size() > 1) {
// Leader working only
if (leading()) {
_appendCV.wait(1000);
// Append entries to followers
sendAppendEntriesRPC();
// Detect faulty agent and replace
// if possible and only if not already activating
if (_activator == nullptr &&
duration<double>(system_clock::now() - tp).count() > 5.0) {
detectActiveAgentFailures();
tp = system_clock::now();
}
} else {
_appendCV.wait(1000000);
updateConfiguration();
}
}
}
void Agent::reportActivated(
std::string const& failed, std::string const& replacement, query_t state) {
_config.swapActiveMember(failed, replacement);
MUTEX_LOCKER(mutexLocker, _ioLock);
_confirmed.erase(failed);
auto commitIndex = state->slice().get("commitIndex").getNumericValue<index_t>();
_confirmed[replacement] = commitIndex;
_lastAcked[replacement] = system_clock::now();
}
void Agent::failedActivation(
std::string const& failed, std::string const& replacement) {
_activator.reset(nullptr);
}
void Agent::detectActiveAgentFailures() {
// Detect faulty agent if pool larger than agency
if (_config.poolSize() > _config.size()) {
std::vector<std::string> active = _config.active();
for (auto const& id : active) {
auto ds = duration<double>(
system_clock::now() - _lastAcked.at(id)).count();
if (ds > 10.0) {
std::string repl = _config.nextAgentInLine();
LOG(WARN) << "Active agent " << id << " has failed. << "
<< repl << " will be promoted to active agency membership";
MUTEX_LOCKER(mutexLocker, _ioLock);
_activator =
std::unique_ptr<AgentActivator>(new AgentActivator(this, id, repl));
}
}
}
}
void Agent::updateConfiguration() {
// First ask last know leader
}
/// 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();
}
for (auto const& i : _config.active()) {
_lastAcked[i] = system_clock::now();
}
// Agency configuration
auto agency = std::make_shared<Builder>();
agency->openArray();
agency->openArray();
agency->openObject();
agency->add(".agency", VPackValue(VPackValueType::Object));
agency->add("term", VPackValue(term()));
agency->add("id", VPackValue(id()));
agency->add("active", _config.activeToBuilder()->slice());
agency->add("pool", _config.poolToBuilder()->slice());
agency->close();
agency->close();
agency->close();
agency->close();
write(agency);
// Wake up supervision
_supervision.wakeUp();
// Notify inactive pool
notifyInactive();
return true;
}
// Notify inactive pool members of configuration change()
void Agent::notifyInactive() const {
if (_config.poolSize() > _config.size()) {
size_t size = _config.size(), counter = 0;
std::map<std::string, std::string> pool = _config.pool();
std::string path = "/_api/agency_priv/inform";
Builder out;
out.openObject();
out.add("term", VPackValue(term()));
out.add("id", VPackValue(id()));
out.add("active", _config.activeToBuilder()->slice());
out.add("pool", _config.poolToBuilder()->slice());
out.close();
for (auto const& p : pool) {
++counter;
if (counter > size) {
auto headerFields =
std::make_unique<std::unordered_map<std::string, std::string>>();
arangodb::ClusterComm::instance()->asyncRequest(
"1", 1, p.second, arangodb::rest::RequestType::POST,
path, std::make_shared<std::string>(out.toJson()), headerFields,
nullptr, 1.0, true);
}
}
}
}
void Agent::notify(query_t const& message) {
VPackSlice slice = message->slice();
if (!slice.isObject()) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20011,
std::string("Inform message must be an object. Incoming type is ") +
slice.typeName());
}
if (!slice.hasKey("id") || !slice.get("id").isString()) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20013, "Inform message must contain string parameter 'id'");
}
if (!slice.hasKey("term")) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20012, "Inform message must contain uint parameter 'term'");
}
_constituent.update(slice.get("id").copyString(),
slice.get("term").getUInt());
if (!slice.hasKey("active") || !slice.get("active").isArray()) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20014, "Inform message must contain array 'active'");
}
if (!slice.hasKey("pool") || !slice.get("pool").isObject()) {
THROW_ARANGO_EXCEPTION_MESSAGE(20015,
"Inform message must contain object 'pool'");
}
_config.update(message);
_state.persistActiveAgents(_config.activeToBuilder(),
_config.poolToBuilder());
}
// Rebuild key value stores
bool Agent::rebuildDBs() {
MUTEX_LOCKER(mutexLocker, _ioLock);
_spearhead.apply(_state.slices(_lastCommitIndex + 1));
_readDB.apply(_state.slices(_lastCommitIndex + 1));
return true;
}
/// Last commit index
arangodb::consensus::index_t Agent::lastCommitted() const {
return _lastCommitIndex;
}
/// Last commit index
void Agent::lastCommitted(arangodb::consensus::index_t lastCommitIndex) {
MUTEX_LOCKER(mutexLocker, _ioLock);
_lastCommitIndex = 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;
}
/// Are we still starting up?
bool Agent::booting() { return (!_config.poolComplete()); }
/// We expect an object as follows {id:<id>,endpoint:<endpoint>,pool:{...}}
/// key: uuid value: endpoint
/// Lock configuration and compare
/// Add whatever is missing in our list.
/// Compare whatever is in our list already. (ASSERT identity)
/// If I know more immediately contact peer with my list.
query_t Agent::gossip(query_t const& in, bool isCallback) {
VPackSlice slice = in->slice();
if (!slice.isObject()) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20001,
std::string("Gossip message must be an object. Incoming type is ") +
slice.typeName());
}
if (!slice.hasKey("id") || !slice.get("id").isString()) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20002, "Gossip message must contain string parameter 'id'");
}
// std::string id = slice.get("id").copyString();
if (!slice.hasKey("endpoint") || !slice.get("endpoint").isString()) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20003, "Gossip message must contain string parameter 'endpoint'");
}
std::string endpoint = slice.get("endpoint").copyString();
LOG_TOPIC(TRACE, Logger::AGENCY)
<< "Gossip " << ((isCallback) ? "callback" : "call") << " from "
<< endpoint;
if (!slice.hasKey("pool") || !slice.get("pool").isObject()) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20003, "Gossip message must contain object parameter 'pool'");
}
VPackSlice pslice = slice.get("pool");
LOG_TOPIC(TRACE, Logger::AGENCY) << "Received gossip " << slice.toJson();
std::map<std::string, std::string> incoming;
for (auto const& pair : VPackObjectIterator(pslice)) {
if (!pair.value.isString()) {
THROW_ARANGO_EXCEPTION_MESSAGE(
20004, "Gossip message pool must contain string parameters");
}
incoming[pair.key.copyString()] = pair.value.copyString();
}
query_t out = std::make_shared<Builder>();
out->openObject();
if (!isCallback) {
std::vector<std::string> gossipPeers = _config.gossipPeers();
if (!gossipPeers.empty()) {
try {
_config.eraseFromGossipPeers(endpoint);
} catch (std::exception const& e) {
LOG_TOPIC(ERR, Logger::AGENCY) << __FILE__ << ":" << __LINE__ << " "
<< e.what();
}
}
size_t counter = 0;
for (auto const& i : incoming) {
if (++counter >
_config.poolSize()) { /// more data than pool size: fatal!
LOG_TOPIC(FATAL, Logger::AGENCY)
<< "Too many peers for poolsize: " << counter << ">"
<< _config.poolSize();
FATAL_ERROR_EXIT();
}
if (!_config.addToPool(i)) {
LOG_TOPIC(FATAL, Logger::AGENCY) << "Discrepancy in agent pool!";
FATAL_ERROR_EXIT();
}
}
// bool send = false;
std::map<std::string, std::string> pool = _config.pool();
out->add("endpoint", VPackValue(_config.endpoint()));
out->add("id", VPackValue(_config.id()));
out->add("pool", VPackValue(VPackValueType::Object));
for (auto const& i : pool) {
out->add(i.first, VPackValue(i.second));
}
out->close();
}
out->close();
LOG_TOPIC(TRACE, Logger::AGENCY) << "Answering with gossip "
<< out->slice().toJson();
return out;
}
}
} // namespace
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