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foundationdb/fdbserver/PaxosConfigConsumer.actor.cpp

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/*
* PaxosConfigConsumer.actor.cpp
*
* This source file is part of the FoundationDB open source project
*
* Copyright 2013-2022 Apple Inc. and the FoundationDB project authors
*
* 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 "fdbserver/PaxosConfigConsumer.h"
#include <algorithm>
#include <map>
#include <numeric>
#include "fdbserver/Knobs.h"
#include "flow/actorcompiler.h" // This must be the last #include.
using ConfigFollowerInfo = ModelInterface<ConfigFollowerInterface>;
struct CommittedVersions {
Version secondToLastCommitted;
Version lastCommitted;
};
struct QuorumVersion {
CommittedVersions versions;
bool isQuorum;
};
class GetCommittedVersionQuorum {
// Set to the <secondToLastCommitted, lastCommitted> versions a quorum of
// ConfigNodes agree on, otherwise unset.
Promise<QuorumVersion> quorumVersion;
std::vector<Future<Void>> actors;
std::vector<ConfigFollowerInterface> cfis;
std::map<Version, std::vector<ConfigFollowerInterface>> replies;
std::map<Version, Version> priorVersions;
std::map<NetworkAddress, Version> committed;
// Need to know the largest compacted version on any node to avoid asking
// for changes that have already been compacted.
Version largestCompactedResponse{ 0 };
// Last durably committed version.
Version lastSeenVersion;
size_t totalRepliesReceived{ 0 };
size_t maxAgreement{ 0 };
// Stores the largest committed version out of all responses.
Version largestCommitted{ 0 };
// Sends rollback/rollforward messages to any nodes that are not up to date
// with the latest committed version as determined by the quorum. Should
// only be called after a committed version has been determined.
ACTOR static Future<Void> updateNode(GetCommittedVersionQuorum* self,
CommittedVersions nodeVersion,
CommittedVersions quorumVersion,
Version lastCompacted,
ConfigFollowerInterface cfi) {
state Version target = quorumVersion.lastCommitted;
if (nodeVersion.lastCommitted == target) {
return Void();
}
if (nodeVersion.lastCommitted < target) {
state Optional<Version> rollback;
if (nodeVersion.lastCommitted > quorumVersion.secondToLastCommitted) {
// If a non-quorum node has a last committed version less than
// the last committed version on the quorum, but greater than
// the second to last committed version on the quorum, it has
// committed changes the quorum does not agree with. Therefore,
// it needs to be rolled back before being rolled forward.
rollback = quorumVersion.secondToLastCommitted;
} else if (nodeVersion.lastCommitted < quorumVersion.secondToLastCommitted) {
// On the other hand, if the node is on an older committed
// version, it's possible the version it is on was never made
// durable. To be safe, roll it back by one version.
rollback = std::max(nodeVersion.lastCommitted - 1, Version{ 0 });
}
if (rollback.present()) {
// When a new ConfigBroadcaster is created, it may not know
// about the last committed version on the ConfigNodes. If
// compaction has occurred, this can cause change requests to
// be sent to nodes asking for version 0 when the node has
// already compacted that version, causing an error. Make sure
// the rollback version is at least set to the last compacted
// version to prevent this issue.
rollback = std::max(rollback.get(), lastCompacted);
}
// Now roll node forward to match the largest committed version of
// the replies.
try {
state std::vector<ConfigFollowerInterface> interfs = self->replies[target];
std::vector<Future<Void>> fs;
for (ConfigFollowerInterface& interf : interfs) {
if (interf.hostname.present()) {
fs.push_back(tryInitializeRequestStream(
&interf.getChanges, interf.hostname.get(), WLTOKEN_CONFIGFOLLOWER_GETCHANGES));
}
}
wait(waitForAll(fs));
state Reference<ConfigFollowerInfo> quorumCfi(new ConfigFollowerInfo(interfs));
state Version lastSeenVersion = std::max(
rollback.present() ? rollback.get() : nodeVersion.lastCommitted, self->largestCompactedResponse);
ConfigFollowerGetChangesReply reply =
wait(timeoutError(basicLoadBalance(quorumCfi,
&ConfigFollowerInterface::getChanges,
ConfigFollowerGetChangesRequest{ lastSeenVersion, target }),
SERVER_KNOBS->GET_COMMITTED_VERSION_TIMEOUT));
if (cfi.hostname.present()) {
wait(timeoutError(
retryGetReplyFromHostname(
ConfigFollowerRollforwardRequest{
rollback, nodeVersion.lastCommitted, target, reply.changes, reply.annotations },
cfi.hostname.get(),
WLTOKEN_CONFIGFOLLOWER_ROLLFORWARD),
SERVER_KNOBS->GET_COMMITTED_VERSION_TIMEOUT));
} else {
wait(timeoutError(
cfi.rollforward.getReply(ConfigFollowerRollforwardRequest{
rollback, nodeVersion.lastCommitted, target, reply.changes, reply.annotations }),
SERVER_KNOBS->GET_COMMITTED_VERSION_TIMEOUT));
}
} catch (Error& e) {
if (e.code() == error_code_transaction_too_old) {
// Seeing this trace is not necessarily a problem. There
// are legitimate scenarios where a ConfigNode could return
// one of these errors in response to a get changes or
// rollforward request. The retry loop should handle this
// case.
TraceEvent(SevInfo, "ConfigNodeRollforwardError").error(e);
} else {
throw;
}
}
}
return Void();
}
ACTOR static Future<Void> getCommittedVersionActor(GetCommittedVersionQuorum* self, ConfigFollowerInterface cfi) {
try {
state ConfigFollowerGetCommittedVersionReply reply;
if (cfi.hostname.present()) {
wait(timeoutError(store(reply,
retryGetReplyFromHostname(ConfigFollowerGetCommittedVersionRequest{},
cfi.hostname.get(),
WLTOKEN_CONFIGFOLLOWER_GETCOMMITTEDVERSION)),
SERVER_KNOBS->GET_COMMITTED_VERSION_TIMEOUT));
} else {
wait(timeoutError(
store(reply, cfi.getCommittedVersion.getReply(ConfigFollowerGetCommittedVersionRequest{})),
SERVER_KNOBS->GET_COMMITTED_VERSION_TIMEOUT));
}
++self->totalRepliesReceived;
self->largestCompactedResponse = std::max(self->largestCompactedResponse, reply.lastCompacted);
state Version lastCompacted = reply.lastCompacted;
self->largestCommitted = std::max(self->largestCommitted, reply.lastCommitted);
state CommittedVersions committedVersions = CommittedVersions{ self->lastSeenVersion, reply.lastCommitted };
if (self->priorVersions.find(committedVersions.lastCommitted) == self->priorVersions.end()) {
self->priorVersions[committedVersions.lastCommitted] = self->lastSeenVersion;
}
auto& nodes = self->replies[committedVersions.lastCommitted];
nodes.push_back(cfi);
self->maxAgreement = std::max(nodes.size(), self->maxAgreement);
if (nodes.size() >= self->cfis.size() / 2 + 1) {
// A quorum of ConfigNodes agree on the latest committed version.
if (self->quorumVersion.canBeSet()) {
self->quorumVersion.send(QuorumVersion{ committedVersions, true });
}
wait(self->updateNode(
self, committedVersions, self->quorumVersion.getFuture().get().versions, lastCompacted, cfi));
} else if (self->maxAgreement >= self->cfis.size() / 2 + 1) {
// A quorum of ConfigNodes agree on the latest committed version,
// but the node we just got a reply from is not one of them. We may
// need to roll it forward or back.
QuorumVersion quorumVersion = wait(self->quorumVersion.getFuture());
ASSERT(committedVersions.lastCommitted != quorumVersion.versions.lastCommitted);
wait(self->updateNode(self, committedVersions, quorumVersion.versions, lastCompacted, cfi));
} else if (self->maxAgreement + (self->cfis.size() - self->totalRepliesReceived) <
(self->cfis.size() / 2 + 1)) {
// It is impossible to reach a quorum of ConfigNodes that agree
// on the same committed version. This breaks "quorum" logic
// slightly in that there is no quorum that agrees on a single
// committed version. So instead we pick the highest committed
// version among the replies and roll all nodes forward to that
// version.
Version largestCommitted = self->replies.rbegin()->first;
Version largestCommittedPrior = self->priorVersions[largestCommitted];
if (self->quorumVersion.canBeSet()) {
self->quorumVersion.send(
QuorumVersion{ CommittedVersions{ largestCommittedPrior, largestCommitted }, false });
}
wait(self->updateNode(
self, committedVersions, self->quorumVersion.getFuture().get().versions, lastCompacted, cfi));
} else {
// Still building up responses; don't have enough data to act on
// yet, so wait until we do.
QuorumVersion quorumVersion = wait(self->quorumVersion.getFuture());
wait(self->updateNode(self, committedVersions, quorumVersion.versions, lastCompacted, cfi));
}
} catch (Error& e) {
// Count a timeout as a reply.
++self->totalRepliesReceived;
if (e.code() == error_code_version_already_compacted) {
if (self->quorumVersion.canBeSet()) {
self->quorumVersion.sendError(e);
}
} else if (e.code() != error_code_timed_out && e.code() != error_code_broken_promise) {
if (self->quorumVersion.canBeSet()) {
self->quorumVersion.sendError(e);
}
} else if (self->totalRepliesReceived == self->cfis.size() && self->quorumVersion.canBeSet() &&
!self->quorumVersion.isError()) {
size_t nonTimeoutReplies =
std::accumulate(self->replies.begin(), self->replies.end(), 0, [](int value, auto const& p) {
return value + p.second.size();
});
if (nonTimeoutReplies >= self->cfis.size() / 2 + 1) {
// Make sure to trigger the quorumVersion if a timeout
// occurred, a quorum disagree on the committed version,
// and there are no more incoming responses. Note that this
// means that it is impossible to reach a quorum, so send
// back the largest committed version seen.
self->quorumVersion.send(
QuorumVersion{ CommittedVersions{ self->lastSeenVersion, self->largestCommitted }, false });
} else if (!self->quorumVersion.isSet()) {
// Otherwise, if a quorum agree on the committed version,
// some other occurred. Notify the caller of it.
self->quorumVersion.sendError(e);
}
}
}
return Void();
}
public:
explicit GetCommittedVersionQuorum(std::vector<ConfigFollowerInterface> const& cfis, Version lastSeenVersion)
: cfis(cfis), lastSeenVersion(lastSeenVersion) {}
Future<QuorumVersion> getCommittedVersion() {
ASSERT(!isReady()); // ensures this function is not accidentally called before resetting state
for (const auto& cfi : cfis) {
actors.push_back(getCommittedVersionActor(this, cfi));
}
return quorumVersion.getFuture();
}
bool isReady() const {
return quorumVersion.getFuture().isValid() && quorumVersion.getFuture().isReady() &&
!quorumVersion.getFuture().isError();
}
std::vector<ConfigFollowerInterface> getReadReplicas() const {
if (quorumVersion.getFuture().isError()) {
throw quorumVersion.getFuture().getError();
}
ASSERT(isReady());
return replies.at(quorumVersion.getFuture().get().versions.lastCommitted);
}
Version getSmallestCommitted() const {
if (committed.size() == cfis.size()) {
Version smallest = MAX_VERSION;
for (const auto& [key, value] : committed) {
smallest = std::min(smallest, value);
}
return smallest;
}
return ::invalidVersion;
}
Future<Void> complete() const { return waitForAll(actors); }
};
class PaxosConfigConsumerImpl {
std::vector<ConfigFollowerInterface> cfis;
GetCommittedVersionQuorum getCommittedVersionQuorum;
Version lastSeenVersion{ 0 };
Version compactionVersion{ 0 };
double pollingInterval;
Optional<double> compactionInterval;
UID id;
ACTOR static Future<Version> getCommittedVersion(PaxosConfigConsumerImpl* self) {
QuorumVersion quorumVersion = wait(self->getCommittedVersionQuorum.getCommittedVersion());
if (!quorumVersion.isQuorum) {
throw failed_to_reach_quorum();
}
return quorumVersion.versions.lastCommitted;
}
// Periodically compact knob changes on the configuration nodes. All nodes
// must have received a version before it can be compacted.
ACTOR static Future<Void> compactor(PaxosConfigConsumerImpl* self, ConfigBroadcaster* broadcaster) {
if (!self->compactionInterval.present()) {
wait(Never());
return Void();
}
loop {
state Version compactionVersion = self->compactionVersion;
wait(delayJittered(self->compactionInterval.get()));
std::vector<Future<Void>> compactionRequests;
compactionRequests.reserve(compactionRequests.size());
for (const auto& cfi : self->cfis) {
if (cfi.hostname.present()) {
compactionRequests.push_back(
retryGetReplyFromHostname(ConfigFollowerCompactRequest{ compactionVersion },
cfi.hostname.get(),
WLTOKEN_CONFIGFOLLOWER_COMPACT));
} else {
compactionRequests.push_back(
cfi.compact.getReply(ConfigFollowerCompactRequest{ compactionVersion }));
}
}
try {
wait(timeoutError(waitForAll(compactionRequests), 1.0));
} catch (Error& e) {
TraceEvent(SevWarn, "ErrorSendingCompactionRequest").error(e);
}
}
}
ACTOR static Future<Void> getSnapshotAndChanges(PaxosConfigConsumerImpl* self, ConfigBroadcaster* broadcaster) {
loop {
self->resetCommittedVersionQuorum(); // TODO: This seems to fix a segfault, investigate more
try {
state Version committedVersion = wait(getCommittedVersion(self));
state std::vector<ConfigFollowerInterface> readReplicas =
self->getCommittedVersionQuorum.getReadReplicas();
std::vector<Future<Void>> fs;
for (ConfigFollowerInterface& readReplica : readReplicas) {
if (readReplica.hostname.present()) {
fs.push_back(tryInitializeRequestStream(&readReplica.getSnapshotAndChanges,
readReplica.hostname.get(),
WLTOKEN_CONFIGFOLLOWER_GETSNAPSHOTANDCHANGES));
}
}
wait(waitForAll(fs));
state Reference<ConfigFollowerInfo> configNodes(new ConfigFollowerInfo(readReplicas));
ConfigFollowerGetSnapshotAndChangesReply reply =
wait(timeoutError(basicLoadBalance(configNodes,
&ConfigFollowerInterface::getSnapshotAndChanges,
ConfigFollowerGetSnapshotAndChangesRequest{ committedVersion }),
SERVER_KNOBS->GET_SNAPSHOT_AND_CHANGES_TIMEOUT));
TraceEvent(SevDebug, "ConfigConsumerGotSnapshotAndChanges", self->id)
.detail("SnapshotVersion", reply.snapshotVersion)
.detail("SnapshotSize", reply.snapshot.size())
.detail("ChangesVersion", committedVersion)
.detail("ChangesSize", reply.changes.size())
.detail("AnnotationsSize", reply.annotations.size());
ASSERT_GE(committedVersion, self->lastSeenVersion);
self->lastSeenVersion = committedVersion;
Version smallestCommitted = self->getCommittedVersionQuorum.getSmallestCommitted();
self->compactionVersion = std::max(self->compactionVersion, smallestCommitted);
broadcaster->applySnapshotAndChanges(std::move(reply.snapshot),
reply.snapshotVersion,
reply.changes,
committedVersion,
reply.annotations,
self->getCommittedVersionQuorum.getReadReplicas());
wait(self->getCommittedVersionQuorum.complete());
break;
} catch (Error& e) {
if (e.code() == error_code_failed_to_reach_quorum) {
wait(self->getCommittedVersionQuorum.complete());
} else if (e.code() != error_code_timed_out && e.code() != error_code_broken_promise &&
e.code() != error_code_version_already_compacted && e.code() != error_code_process_behind) {
throw;
}
wait(delayJittered(0.1));
self->resetCommittedVersionQuorum();
}
}
return Void();
}
ACTOR static Future<Void> fetchChanges(PaxosConfigConsumerImpl* self, ConfigBroadcaster* broadcaster) {
wait(getSnapshotAndChanges(self, broadcaster));
self->resetCommittedVersionQuorum();
loop {
try {
state Version committedVersion = wait(getCommittedVersion(self));
// Because the committed version returned can be a value not
// accepted by a quorum, it is possible to read a committed
// version less than the last seen committed version.
// Specifically, if a new consumer starts and reads a snapshot
// with ConfigNodes at versions 0, 1, 2, it will return a
// committed version of 2. Later, if the configuration of the
// ConfigNodes changes to 1, 1, 2, the committed version
// returned would be 1.
if (committedVersion > self->lastSeenVersion) {
ASSERT(self->getCommittedVersionQuorum.getReadReplicas().size() >= self->cfis.size() / 2 + 1);
state std::vector<ConfigFollowerInterface> readReplicas =
self->getCommittedVersionQuorum.getReadReplicas();
std::vector<Future<Void>> fs;
for (ConfigFollowerInterface& readReplica : readReplicas) {
if (readReplica.hostname.present()) {
fs.push_back(tryInitializeRequestStream(&readReplica.getChanges,
readReplica.hostname.get(),
WLTOKEN_CONFIGFOLLOWER_GETCHANGES));
}
}
wait(waitForAll(fs));
state Reference<ConfigFollowerInfo> configNodes(new ConfigFollowerInfo(readReplicas));
ConfigFollowerGetChangesReply reply = wait(timeoutError(
basicLoadBalance(configNodes,
&ConfigFollowerInterface::getChanges,
ConfigFollowerGetChangesRequest{ self->lastSeenVersion, committedVersion }),
SERVER_KNOBS->FETCH_CHANGES_TIMEOUT));
for (const auto& versionedMutation : reply.changes) {
TraceEvent te(SevDebug, "ConsumerFetchedMutation", self->id);
te.detail("Version", versionedMutation.version)
.detail("ConfigClass", versionedMutation.mutation.getConfigClass())
.detail("KnobName", versionedMutation.mutation.getKnobName());
if (versionedMutation.mutation.isSet()) {
te.detail("Op", "Set")
.detail("KnobValue", versionedMutation.mutation.getValue().toString());
} else {
te.detail("Op", "Clear");
}
}
self->lastSeenVersion = committedVersion;
Version smallestCommitted = self->getCommittedVersionQuorum.getSmallestCommitted();
self->compactionVersion = std::max(self->compactionVersion, smallestCommitted);
broadcaster->applyChanges(reply.changes,
committedVersion,
reply.annotations,
self->getCommittedVersionQuorum.getReadReplicas());
} else if (committedVersion == self->lastSeenVersion) {
broadcaster->applyChanges({}, -1, {}, self->getCommittedVersionQuorum.getReadReplicas());
}
wait(delayJittered(self->pollingInterval));
} catch (Error& e) {
if (e.code() == error_code_version_already_compacted || e.code() == error_code_timed_out ||
e.code() == error_code_failed_to_reach_quorum || e.code() == error_code_version_already_compacted ||
e.code() == error_code_process_behind) {
TEST(true); // PaxosConfigConsumer get version_already_compacted error
if (e.code() == error_code_failed_to_reach_quorum) {
try {
wait(self->getCommittedVersionQuorum.complete());
} catch (Error& e) {
if (e.code() == error_code_broken_promise) {
self->resetCommittedVersionQuorum();
continue;
} else {
throw;
}
}
}
self->resetCommittedVersionQuorum();
wait(getSnapshotAndChanges(self, broadcaster));
} else if (e.code() == error_code_broken_promise) {
self->resetCommittedVersionQuorum();
continue;
} else {
throw;
}
}
try {
wait(self->getCommittedVersionQuorum.complete());
} catch (Error& e) {
if (e.code() != error_code_broken_promise) {
throw;
}
}
self->resetCommittedVersionQuorum();
}
}
void resetCommittedVersionQuorum() {
getCommittedVersionQuorum = GetCommittedVersionQuorum{ cfis, lastSeenVersion };
}
public:
Future<Void> consume(ConfigBroadcaster& broadcaster) {
return fetchChanges(this, &broadcaster) || compactor(this, &broadcaster);
}
UID getID() const { return id; }
PaxosConfigConsumerImpl(std::vector<ConfigFollowerInterface> const& cfis,
double pollingInterval,
Optional<double> compactionInterval)
: cfis(cfis), getCommittedVersionQuorum(cfis, 0), pollingInterval(pollingInterval),
compactionInterval(compactionInterval), id(deterministicRandom()->randomUniqueID()) {}
};
PaxosConfigConsumer::PaxosConfigConsumer(std::vector<ConfigFollowerInterface> const& cfis,
double pollingInterval,
Optional<double> compactionInterval)
: impl(PImpl<PaxosConfigConsumerImpl>::create(cfis, pollingInterval, compactionInterval)) {}
PaxosConfigConsumer::PaxosConfigConsumer(ServerCoordinators const& coordinators,
double pollingInterval,
Optional<double> compactionInterval)
: impl(PImpl<PaxosConfigConsumerImpl>::create(coordinators.configServers, pollingInterval, compactionInterval)) {}
PaxosConfigConsumer::~PaxosConfigConsumer() = default;
Future<Void> PaxosConfigConsumer::consume(ConfigBroadcaster& broadcaster) {
return impl->consume(broadcaster);
}
UID PaxosConfigConsumer::getID() const {
return impl->getID();
}
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