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arangodb/arangod/Agency/RemoveFollower.cpp

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////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2018-2018 ArangoDB 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 Andreas Streichardt
////////////////////////////////////////////////////////////////////////////////
#include "RemoveFollower.h"
#include "Agency/AgentInterface.h"
#include "Agency/Job.h"
#include "Cluster/ClusterInfo.h"
#include "Random/RandomGenerator.h"
using namespace arangodb::consensus;
RemoveFollower::RemoveFollower(Node const& snapshot, AgentInterface* agent,
std::string const& jobId, std::string const& creator,
std::string const& database,
std::string const& collection, std::string const& shard)
: Job(NOTFOUND, snapshot, agent, jobId, creator),
_database(database),
_collection(collection),
_shard(shard) {}
RemoveFollower::RemoveFollower(Node const& snapshot, AgentInterface* agent,
JOB_STATUS status, std::string const& jobId)
: Job(status, snapshot, agent, jobId) {
// Get job details from agency:
std::string path = pos[status] + _jobId + "/";
auto tmp_database = _snapshot.hasAsString(path + "database");
auto tmp_collection = _snapshot.hasAsString(path + "collection");
auto tmp_shard = _snapshot.hasAsString(path + "shard");
auto tmp_creator = _snapshot.hasAsString(path + "creator");
if (tmp_database.second && tmp_collection.second && tmp_shard.second &&
tmp_creator.second) {
_database = tmp_database.first;
_collection = tmp_collection.first;
_shard = tmp_shard.first;
_creator = tmp_creator.first;
} else {
std::stringstream err;
err << "Failed to find job " << _jobId << " in agency.";
LOG_TOPIC("ac178", ERR, Logger::SUPERVISION) << err.str();
finish("", tmp_shard.first, false, err.str());
_status = FAILED;
}
}
RemoveFollower::~RemoveFollower() {}
void RemoveFollower::run(bool& aborts) { runHelper("", _shard, aborts); }
bool RemoveFollower::create(std::shared_ptr<VPackBuilder> envelope) {
LOG_TOPIC("26152", DEBUG, Logger::SUPERVISION)
<< "Todo: RemoveFollower(s) "
<< " to shard " << _shard << " in collection " << _collection;
bool selfCreate = (envelope == nullptr); // Do we create ourselves?
if (selfCreate) {
_jb = std::make_shared<Builder>();
} else {
_jb = envelope;
}
std::string now(timepointToString(std::chrono::system_clock::now()));
if (selfCreate) {
_jb->openArray();
_jb->openObject();
}
std::string path = toDoPrefix + _jobId;
_jb->add(VPackValue(path));
{
VPackObjectBuilder guard(_jb.get());
_jb->add("creator", VPackValue(_creator));
_jb->add("type", VPackValue("removeFollower"));
_jb->add("database", VPackValue(_database));
_jb->add("collection", VPackValue(_collection));
_jb->add("shard", VPackValue(_shard));
_jb->add("jobId", VPackValue(_jobId));
_jb->add("timeCreated", VPackValue(now));
}
_status = TODO;
if (!selfCreate) {
return true;
}
_jb->close(); // transaction object
_jb->close(); // close array
write_ret_t res = singleWriteTransaction(_agent, *_jb);
if (res.accepted && res.indices.size() == 1 && res.indices[0]) {
return true;
}
_status = NOTFOUND;
LOG_TOPIC("83bf8", INFO, Logger::SUPERVISION) << "Failed to insert job " + _jobId;
return false;
}
bool RemoveFollower::start(bool&) {
// If anything throws here, the run() method catches it and finishes
// the job.
// Are we distributeShardsLiking other shard? Then fail miserably.
if (!_snapshot.has(planColPrefix + _database + "/" + _collection)) {
finish("", "", true, "collection has been dropped in the meantime");
return false;
}
Node collection =
_snapshot.hasAsNode(planColPrefix + _database + "/" + _collection).first;
if (collection.has("distributeShardsLike")) {
finish("", "", false,
"collection must not have 'distributeShardsLike' attribute");
return false;
}
// Look at Plan:
std::string planPath =
planColPrefix + _database + "/" + _collection + "/shards/" + _shard;
Slice planned = _snapshot.hasAsSlice(planPath).first;
TRI_ASSERT(planned.isArray());
// First check that we still have too many followers for the current
// `replicationFactor`:
size_t desiredReplFactor = 1;
auto replFact = collection.hasAsUInt("replicationFactor");
if (replFact.second) {
desiredReplFactor = replFact.first;
} else {
auto replFact2 = collection.hasAsString("replicationFactor");
if (replFact2.second && replFact2.first == "satellite") {
// satellites => distribute to every server
auto available = Job::availableServers(_snapshot);
desiredReplFactor = Job::countGoodOrBadServersInList(_snapshot, available);
}
}
size_t actualReplFactor = planned.length();
if (actualReplFactor <= desiredReplFactor) {
finish("", "", true, "job no longer necessary, have few enough replicas");
return true;
}
// Check that the shard is not locked:
if (_snapshot.has(blockedShardsPrefix + _shard)) {
LOG_TOPIC("cef47", DEBUG, Logger::SUPERVISION)
<< "shard " << _shard
<< " is currently locked, not starting RemoveFollower job " << _jobId;
return false;
}
// Find the group of shards that are distributed alike:
std::vector<Job::shard_t> shardsLikeMe =
clones(_snapshot, _database, _collection, _shard);
// Now find some new servers to remove:
std::unordered_map<std::string, int> overview; // get an overview over the servers
// -1 : not "GOOD", can be in sync, or leader, or not
// >=0: number of servers for which it is in sync or confirmed leader
bool leaderBad = false;
for (auto const& srv : VPackArrayIterator(planned)) {
std::string serverName = srv.copyString();
if (checkServerHealth(_snapshot, serverName) == "GOOD") {
overview.emplace(serverName, 0);
} else {
overview.emplace(serverName, -1);
if (serverName == planned[0].copyString()) {
leaderBad = true;
}
}
}
doForAllShards(_snapshot, _database, shardsLikeMe,
[&planned, &overview, &leaderBad](Slice plan, Slice current,
std::string& planPath, std::string& curPath) {
if (current.length() > 0) {
if (current[0].copyString() != planned[0].copyString()) {
leaderBad = true;
} else {
for (auto const s : VPackArrayIterator(current)) {
auto it = overview.find(s.copyString());
if (it != overview.end()) {
if (it->second >= 0) {
++(it->second);
}
}
}
}
} else {
leaderBad = true;
}
});
size_t inSyncCount = 0;
size_t notGoodCount = 0;
for (auto const& pair : overview) {
if (pair.second == -1) {
++notGoodCount;
} else if (static_cast<size_t>(pair.second) >= shardsLikeMe.size()) {
++inSyncCount;
}
}
// Check that leader is OK for all shards:
if (leaderBad) {
LOG_TOPIC("d4845", DEBUG, Logger::SUPERVISION)
<< "shard " << _shard
<< " does not have a leader that has confirmed leadership, waiting, "
"jobId="
<< _jobId;
finish("", "", false, "job no longer sensible, leader has gone bad");
return false;
}
// Check that we have enough:
if (inSyncCount < desiredReplFactor) {
LOG_TOPIC("d9118", DEBUG, Logger::SUPERVISION)
<< "shard " << _shard
<< " does not have enough in sync followers to remove one, waiting, "
"jobId="
<< _jobId;
finish("", "", false, "job no longer sensible, do not have few enough replicas");
return true;
}
// We now know actualReplFactor >= inSyncCount + noGoodCount and
// inSyncCount >= desiredReplFactor
// Let notInSyncCount = actualReplFactor - (inSyncCount + noGoodCount)
// To reduce actualReplFactor down to desiredReplFactor we
// Randomly choose enough servers:
std::unordered_set<std::string> chosenToRemove;
size_t currentReplFactor = actualReplFactor; // will be counted down
if (currentReplFactor > desiredReplFactor) {
// First choose BAD servers:
// Iterate the list of planned servers in reverse order,
// because the last must be removed first
std::vector<ServerID> reversedPlannedServers{planned.length()};
{
auto rDbIt = reversedPlannedServers.rbegin();
for (auto const& vPackIt : VPackArrayIterator(planned)) {
*rDbIt = vPackIt.copyString();
rDbIt++;
}
}
for (auto const& it : reversedPlannedServers) {
auto const pair = *overview.find(it);
if (pair.second == -1) {
chosenToRemove.insert(pair.first);
--currentReplFactor;
}
if (currentReplFactor == desiredReplFactor) {
break;
}
}
if (currentReplFactor > desiredReplFactor) {
// Now choose servers that are not in sync for all shards:
for (auto const& it : reversedPlannedServers) {
auto const pair = *overview.find(it);
if (pair.second >= 0 && static_cast<size_t>(pair.second) < shardsLikeMe.size()) {
chosenToRemove.insert(pair.first);
--currentReplFactor;
}
if (currentReplFactor == desiredReplFactor) {
break;
}
}
if (currentReplFactor > desiredReplFactor) {
// Finally choose servers that are in sync, but are no leader:
for (auto const& it : reversedPlannedServers) {
auto const pair = *overview.find(it);
if (pair.second >= 0 &&
static_cast<size_t>(pair.second) >= shardsLikeMe.size() &&
pair.first != planned[0].copyString()) {
if (Job::isInServerList(_snapshot, toBeCleanedPrefix, pair.first, true) ||
Job::isInServerList(_snapshot, cleanedPrefix, pair.first, true)) {
// Prefer those cleaned or to be cleaned servers
chosenToRemove.insert(pair.first);
--currentReplFactor;
}
}
if (currentReplFactor == desiredReplFactor) {
break;
}
}
if (currentReplFactor > desiredReplFactor) {
// Now allow those which are perfectly good as well:
for (auto const& it : reversedPlannedServers) {
auto const pair = *overview.find(it);
if (pair.second >= 0 &&
static_cast<size_t>(pair.second) >= shardsLikeMe.size() &&
pair.first != planned[0].copyString()) {
if (!Job::isInServerList(_snapshot, toBeCleanedPrefix, pair.first, true) &&
!Job::isInServerList(_snapshot, cleanedPrefix, pair.first, true)) {
chosenToRemove.insert(pair.first);
--currentReplFactor;
}
}
if (currentReplFactor == desiredReplFactor) {
break;
}
}
}
}
}
}
std::vector<std::string> kept;
for (auto const& srv : VPackArrayIterator(planned)) {
std::string serverName = srv.copyString();
if (chosenToRemove.find(serverName) == chosenToRemove.end()) {
kept.push_back(serverName);
}
}
// Copy todo to finished:
Builder todo, trx;
// Get todo entry
{
VPackArrayBuilder guard(&todo);
// When create() was done with the current snapshot, then the job object
// will not be in the snapshot under ToDo, but in this case we find it
// in _jb:
if (_jb == nullptr) {
auto tmp_todo = _snapshot.hasAsBuilder(toDoPrefix + _jobId, todo);
if (!tmp_todo.second) {
// Just in case, this is never going to happen, since we will only
// call the start() method if the job is already in ToDo.
LOG_TOPIC("4fac6", INFO, Logger::SUPERVISION) << "Failed to get key " + toDoPrefix + _jobId +
" from agency snapshot";
return false;
}
} else {
try {
todo.add(_jb->slice()[0].get(toDoPrefix + _jobId));
} catch (std::exception const& e) {
// Just in case, this is never going to happen, since when _jb is
// set, then the current job is stored under ToDo.
LOG_TOPIC("95927", WARN, Logger::SUPERVISION)
<< e.what() << ": " << __FILE__ << ":" << __LINE__;
return false;
}
}
}
// Enter pending, remove todo, block toserver
{
VPackArrayBuilder listOfTransactions(&trx);
{
VPackObjectBuilder objectForMutation(&trx);
addPutJobIntoSomewhere(trx, "Finished", todo.slice()[0]);
addRemoveJobFromSomewhere(trx, "ToDo", _jobId);
// --- Plan changes
doForAllShards(_snapshot, _database, shardsLikeMe,
[&trx, &chosenToRemove](Slice plan, Slice current, std::string& planPath, std::string& curPath) {
trx.add(VPackValue(planPath));
{
VPackArrayBuilder serverList(&trx);
for (auto const& srv : VPackArrayIterator(plan)) {
if (chosenToRemove.find(srv.copyString()) ==
chosenToRemove.end()) {
trx.add(srv);
}
}
}
});
addIncreasePlanVersion(trx);
} // mutation part of transaction done
// Preconditions
{
VPackObjectBuilder precondition(&trx);
// --- Check that Planned servers are still as we expect
addPreconditionUnchanged(trx, planPath, planned);
addPreconditionShardNotBlocked(trx, _shard);
for (auto const& srv : kept) {
addPreconditionServerHealth(trx, srv, "GOOD");
}
} // precondition done
} // array for transaction done
// Transact to agency
write_ret_t res = singleWriteTransaction(_agent, trx);
if (res.accepted && res.indices.size() == 1 && res.indices[0]) {
_status = FINISHED;
LOG_TOPIC("9ec40", DEBUG, Logger::SUPERVISION)
<< "Pending: RemoveFollower(s) to shard " << _shard << " in collection "
<< _collection;
return true;
}
LOG_TOPIC("f2df8", INFO, Logger::SUPERVISION)
<< "Start precondition failed for RemoveFollower Job " + _jobId;
return false;
}
JOB_STATUS RemoveFollower::status() {
if (_status != PENDING) {
return _status;
}
TRI_ASSERT(false); // PENDING is not an option for this job, since it
// travels directly from ToDo to Finished or Failed
return _status;
}
arangodb::Result RemoveFollower::abort() {
Result result;
// We can assume that the job is in ToDo or not there:
if (_status == NOTFOUND || _status == FINISHED || _status == FAILED) {
result =
Result(1, "Failed aborting RemoveFollower job beyond pending stage");
return result;
}
// Can now only be TODO or PENDING
if (_status == TODO) {
finish("", "", false, "job aborted");
return result;
}
TRI_ASSERT(false); // cannot happen, since job moves directly to FINISHED
return result;
}
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