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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kStorage
#include "mongo/platform/basic.h"
#include "mongo/db/db_raii.h"
#include "mongo/db/catalog/database_holder.h"
#include "mongo/db/concurrency/locker.h"
#include "mongo/db/curop.h"
#include "mongo/db/repl/replication_coordinator.h"
#include "mongo/db/s/collection_sharding_state.h"
#include "mongo/db/storage/snapshot_helper.h"
#include "mongo/logv2/log.h"
namespace mongo {
namespace {
const boost::optional<int> kDoNotChangeProfilingLevel = boost::none;
// TODO: SERVER-44105 remove
// If set to false, secondary reads should wait behind the PBW lock.
const auto allowSecondaryReadsDuringBatchApplication_DONT_USE =
OperationContext::declareDecoration<boost::optional<bool>>();
/**
* Performs some checks to determine whether the operation is compatible with a lock-free read.
* The DBDirectClient and multi-doc transactions are not supported.
*/
bool supportsLockFreeRead(OperationContext* opCtx) {
// Lock-free reads are only supported for external queries, not internal via DBDirectClient.
// Lock-free reads are not supported in multi-document transactions.
return !opCtx->getClient()->isInDirectClient() && !opCtx->inMultiDocumentTransaction();
}
} // namespace
AutoStatsTracker::AutoStatsTracker(OperationContext* opCtx,
const NamespaceString& nss,
Top::LockType lockType,
LogMode logMode,
int dbProfilingLevel,
Date_t deadline)
: _opCtx(opCtx), _lockType(lockType), _nss(nss), _logMode(logMode) {
if (_logMode == LogMode::kUpdateTop) {
return;
}
stdx::lock_guard<Client> clientLock(*_opCtx->getClient());
CurOp::get(_opCtx)->enter_inlock(_nss.ns().c_str(), dbProfilingLevel);
}
AutoStatsTracker::~AutoStatsTracker() {
if (_logMode == LogMode::kUpdateCurOp) {
return;
}
auto curOp = CurOp::get(_opCtx);
Top::get(_opCtx->getServiceContext())
.record(_opCtx,
_nss.ns(),
curOp->getLogicalOp(),
_lockType,
durationCount<Microseconds>(curOp->elapsedTimeExcludingPauses()),
curOp->isCommand(),
curOp->getReadWriteType());
}
template <typename AutoGetCollectionType>
AutoGetCollectionForReadBase<AutoGetCollectionType>::AutoGetCollectionForReadBase(
OperationContext* opCtx,
const NamespaceStringOrUUID& nsOrUUID,
AutoGetCollectionViewMode viewMode,
Date_t deadline) {
// The caller was expecting to conflict with batch application before entering this function.
// i.e. the caller does not currently have a ShouldNotConflict... block in scope.
bool callerWasConflicting = opCtx->lockState()->shouldConflictWithSecondaryBatchApplication();
if (allowSecondaryReadsDuringBatchApplication_DONT_USE(opCtx).value_or(true) &&
opCtx->getServiceContext()->getStorageEngine()->supportsReadConcernSnapshot()) {
_shouldNotConflictWithSecondaryBatchApplicationBlock.emplace(opCtx->lockState());
}
// Multi-document transactions need MODE_IX locks, otherwise MODE_IS.
const auto collectionLockMode = getLockModeForQuery(opCtx, nsOrUUID.nss());
_autoColl.emplace(opCtx, nsOrUUID, collectionLockMode, viewMode, deadline);
repl::ReplicationCoordinator* const replCoord = repl::ReplicationCoordinator::get(opCtx);
const auto readConcernLevel = repl::ReadConcernArgs::get(opCtx).getLevel();
// If the collection doesn't exist or disappears after releasing locks and waiting, there is no
// need to check for pending catalog changes.
while (const auto& coll = _autoColl->getCollection()) {
// Ban snapshot reads on capped collections.
uassert(ErrorCodes::SnapshotUnavailable,
"Reading from capped collections with readConcern snapshot is not supported",
!coll->isCapped() ||
readConcernLevel != repl::ReadConcernLevel::kSnapshotReadConcern);
// During batch application on secondaries, there is a potential to read inconsistent states
// that would normally be protected by the PBWM lock. In order to serve secondary reads
// during this period, we default to not acquiring the lock (by setting
// _shouldNotConflictWithSecondaryBatchApplicationBlock). On primaries, we always read at a
// consistent time, so not taking the PBWM lock is not a problem. On secondaries, we have to
// guarantee we read at a consistent state, so we must read at the lastApplied timestamp,
// which is set after each complete batch.
const NamespaceString nss = coll->ns();
auto readSource = opCtx->recoveryUnit()->getTimestampReadSource();
// Once we have our locks, check whether or not we should override the ReadSource that was
// set before acquiring locks.
if (auto newReadSource = SnapshotHelper::getNewReadSource(opCtx, nss)) {
opCtx->recoveryUnit()->setTimestampReadSource(*newReadSource);
readSource = *newReadSource;
}
const auto readTimestamp = opCtx->recoveryUnit()->getPointInTimeReadTimestamp();
const auto afterClusterTime = repl::ReadConcernArgs::get(opCtx).getArgsAfterClusterTime();
if (readTimestamp && afterClusterTime) {
// Readers that use afterClusterTime have already waited at a higher level for the
// all_durable time to advance to a specified optime, and they assume the read timestamp
// of the operation is at least that waited-for timestamp. For kNoOverlap, which is
// the minimum of lastApplied and all_durable, this invariant ensures that
// afterClusterTime reads do not choose a read timestamp older than the one requested.
invariant(*readTimestamp >= afterClusterTime->asTimestamp(),
str::stream() << "read timestamp " << readTimestamp->toString()
<< "was less than afterClusterTime: "
<< afterClusterTime->asTimestamp().toString());
}
// This assertion protects operations from reading inconsistent data on secondaries when
// using the default ReadSource of kNoTimestamp.
// Reading at lastApplied on secondaries is the safest behavior and is enabled for all user
// and DBDirectClient reads using 'local' and 'available' readConcerns. If an internal
// operation wishes to read without a timestamp during a batch, a ShouldNotConflict can
// suppress this fatal assertion with the following considerations:
// * The operation is not reading replicated data in a replication state where batch
// application is active OR
// * Reading inconsistent, out-of-order data is either inconsequential or required by
// the operation.
// If the caller entered this function expecting to conflict with batch application
// (i.e. no ShouldNotConflict block in scope), but they are reading without a timestamp and
// not holding the PBWM lock, then there is a possibility that this reader may
// unintentionally see inconsistent data during a batch. Certain namespaces are applied
// serially in oplog application, and therefore can be safely read without taking the PBWM
// lock or reading at a timestamp.
if (readSource == RecoveryUnit::ReadSource::kNoTimestamp && callerWasConflicting &&
!nss.mustBeAppliedInOwnOplogBatch() &&
SnapshotHelper::shouldReadAtLastApplied(opCtx, nss)) {
LOGV2_FATAL(4728700,
"Reading from replicated collection on a secondary without read timestamp "
"or PBWM lock",
"collection"_attr = nss);
}
auto minSnapshot = coll->getMinimumVisibleSnapshot();
if (!SnapshotHelper::collectionChangesConflictWithRead(minSnapshot, readTimestamp)) {
return;
}
// If we are reading at a provided timestamp earlier than the latest catalog changes,
// then we must return an error.
if (readSource == RecoveryUnit::ReadSource::kProvided) {
uasserted(ErrorCodes::SnapshotUnavailable,
str::stream()
<< "Unable to read from a snapshot due to pending collection catalog "
"changes; please retry the operation. Snapshot timestamp is "
<< readTimestamp->toString() << ". Collection minimum is "
<< minSnapshot->toString());
}
invariant(
// The kMajorityCommitted and kLastApplied read sources already read from timestamps
// that are safe with respect to concurrent secondary batch application, and are
// eligible for retrying.
readSource == RecoveryUnit::ReadSource::kMajorityCommitted ||
readSource == RecoveryUnit::ReadSource::kNoOverlap ||
readSource == RecoveryUnit::ReadSource::kLastApplied);
invariant(readConcernLevel != repl::ReadConcernLevel::kSnapshotReadConcern);
// Yield locks in order to do the blocking call below.
_autoColl = boost::none;
// If there are pending catalog changes when using a no-overlap or lastApplied read source,
// we yield to get a new read timestamp ahead of the minimum visible snapshot.
if (readSource == RecoveryUnit::ReadSource::kLastApplied ||
readSource == RecoveryUnit::ReadSource::kNoOverlap) {
invariant(readTimestamp);
LOGV2(20576,
"Tried reading at a timestamp, but future catalog changes are pending. "
"Trying again",
"readTimestamp"_attr = *readTimestamp,
"collection"_attr = nss.ns(),
"collectionMinSnapshot"_attr = *minSnapshot);
// If we are AutoGetting multiple collections, it is possible that we've already done
// some reads and locked in our snapshot. At this point, the only way out is to fail
// the operation. The client application will need to retry.
uassert(
ErrorCodes::SnapshotUnavailable,
str::stream() << "Unable to read from a snapshot due to pending collection catalog "
"changes and holding multiple collection locks; please retry the "
"operation. Snapshot timestamp is "
<< readTimestamp->toString() << ". Collection minimum is "
<< minSnapshot->toString(),
!opCtx->lockState()->isLocked());
// Abandon our snapshot. We may select a new read timestamp or ReadSource in the next
// loop iteration.
opCtx->recoveryUnit()->abandonSnapshot();
}
if (readSource == RecoveryUnit::ReadSource::kMajorityCommitted) {
replCoord->waitUntilSnapshotCommitted(opCtx, *minSnapshot);
uassertStatusOK(opCtx->recoveryUnit()->obtainMajorityCommittedSnapshot());
}
{
stdx::lock_guard<Client> lk(*opCtx->getClient());
CurOp::get(opCtx)->yielded();
}
_autoColl.emplace(opCtx, nsOrUUID, collectionLockMode, viewMode, deadline);
}
}
AutoGetCollectionForReadLockFree::AutoGetCollectionForReadLockFree(
OperationContext* opCtx,
const NamespaceStringOrUUID& nsOrUUID,
AutoGetCollectionViewMode viewMode,
Date_t deadline) {
// Supported lock-free reads should never have an open storage snapshot prior to calling
// this helper. The storage snapshot and in-memory state fetched here must be consistent.
invariant(supportsLockFreeRead(opCtx) && !opCtx->recoveryUnit()->inActiveTxn());
while (true) {
// AutoGetCollectionForReadBase can choose a read source based on the current replication
// state. Therefore we must fetch the repl state beforehand, to compare with afterwards.
long long replTerm = repl::ReplicationCoordinator::get(opCtx)->getTerm();
_autoGetCollectionForReadBase.emplace(opCtx, nsOrUUID, viewMode, deadline);
// A lock request does not always find a collection to lock.
if (!_autoGetCollectionForReadBase.get()) {
break;
}
// We must open a storage snapshot consistent with the fetched in-memory Collection instance
// and chosen read source. The Collection instance and replication state after opening a
// snapshot will be compared with the previously acquired state. If either does not match,
// then this loop will retry lock acquisition and read source selection until there is a
// match.
//
// Note: AutoGetCollectionForReadBase may open a snapshot for PIT reads, so
// preallocateSnapshot() may be a no-op, but that is OK because the snapshot is established
// by _autoGetCollectionForReadBase after it fetches a Collection instance.
if (_autoGetCollectionForReadBase->getNss().isOplog()) {
// Signal to the RecoveryUnit that the snapshot will be used for reading the oplog.
// Normally the snapshot is opened from a cursor that can take special action when
// reading from the oplog.
opCtx->recoveryUnit()->preallocateSnapshotForOplogRead();
} else {
opCtx->recoveryUnit()->preallocateSnapshot();
}
auto newCollection = CollectionCatalog::get(opCtx).lookupCollectionByUUIDForRead(
opCtx, _autoGetCollectionForReadBase.get()->uuid());
// The collection may have been dropped since the previous lookup, run the loop one more
// time to cleanup
if (!newCollection) {
continue;
}
if (_autoGetCollectionForReadBase.get()->getMinimumVisibleSnapshot() ==
newCollection->getMinimumVisibleSnapshot() &&
replTerm == repl::ReplicationCoordinator::get(opCtx)->getTerm()) {
break;
}
LOGV2_DEBUG(5067701,
3,
"Retrying acquiring state for lock-free read because collection or replication "
"state changed.");
_autoGetCollectionForReadBase.reset();
opCtx->recoveryUnit()->abandonSnapshot();
}
}
AutoGetCollectionForReadMaybeLockFree::AutoGetCollectionForReadMaybeLockFree(
OperationContext* opCtx,
const NamespaceStringOrUUID& nsOrUUID,
AutoGetCollectionViewMode viewMode,
Date_t deadline) {
if (supportsLockFreeRead(opCtx)) {
_autoGetLockFree.emplace(opCtx, nsOrUUID, viewMode, deadline);
} else {
_autoGet.emplace(opCtx, nsOrUUID, viewMode, deadline);
}
}
ViewDefinition* AutoGetCollectionForReadMaybeLockFree::getView() const {
if (_autoGet) {
return _autoGet->getView();
} else {
return _autoGetLockFree->getView();
}
}
const NamespaceString& AutoGetCollectionForReadMaybeLockFree::getNss() const {
if (_autoGet) {
return _autoGet->getNss();
} else {
return _autoGetLockFree->getNss();
}
}
const CollectionPtr& AutoGetCollectionForReadMaybeLockFree::getCollection() const {
if (_autoGet) {
return _autoGet->getCollection();
} else {
return _autoGetLockFree->getCollection();
}
}
template <typename AutoGetCollectionForReadType>
AutoGetCollectionForReadCommandBase<AutoGetCollectionForReadType>::
AutoGetCollectionForReadCommandBase(OperationContext* opCtx,
const NamespaceStringOrUUID& nsOrUUID,
AutoGetCollectionViewMode viewMode,
Date_t deadline,
AutoStatsTracker::LogMode logMode)
: _autoCollForRead(opCtx, nsOrUUID, viewMode, deadline),
_statsTracker(
opCtx,
_autoCollForRead.getNss(),
Top::LockType::ReadLocked,
logMode,
CollectionCatalog::get(opCtx).getDatabaseProfileLevel(_autoCollForRead.getNss().db()),
deadline) {
if (!_autoCollForRead.getView()) {
auto* const css = CollectionShardingState::get(opCtx, _autoCollForRead.getNss());
css->checkShardVersionOrThrow(opCtx);
}
}
OldClientContext::OldClientContext(OperationContext* opCtx, const std::string& ns, bool doVersion)
: _opCtx(opCtx), _db(DatabaseHolder::get(opCtx)->getDb(opCtx, ns)) {
if (!_db) {
const auto dbName = nsToDatabaseSubstring(ns);
_db = DatabaseHolder::get(opCtx)->openDb(_opCtx, dbName, &_justCreated);
invariant(_db);
}
auto const currentOp = CurOp::get(_opCtx);
if (doVersion) {
switch (currentOp->getNetworkOp()) {
case dbGetMore: // getMore is special and should be handled elsewhere
case dbUpdate: // update & delete check shard version as part of the write executor
case dbDelete: // path, so no need to check them here as well
break;
default:
CollectionShardingState::get(_opCtx, NamespaceString(ns))
->checkShardVersionOrThrow(_opCtx);
break;
}
}
stdx::lock_guard<Client> lk(*_opCtx->getClient());
currentOp->enter_inlock(ns.c_str(),
CollectionCatalog::get(opCtx).getDatabaseProfileLevel(_db->name()));
}
AutoGetCollectionForReadCommandMaybeLockFree::AutoGetCollectionForReadCommandMaybeLockFree(
OperationContext* opCtx,
const NamespaceStringOrUUID& nsOrUUID,
AutoGetCollectionViewMode viewMode,
Date_t deadline,
AutoStatsTracker::LogMode logMode) {
if (supportsLockFreeRead(opCtx)) {
_autoGetLockFree.emplace(opCtx, nsOrUUID, viewMode, deadline, logMode);
} else {
_autoGet.emplace(opCtx, nsOrUUID, viewMode, deadline, logMode);
}
}
const CollectionPtr& AutoGetCollectionForReadCommandMaybeLockFree::getCollection() const {
if (_autoGet) {
return _autoGet->getCollection();
} else {
return _autoGetLockFree->getCollection();
}
}
ViewDefinition* AutoGetCollectionForReadCommandMaybeLockFree::getView() const {
if (_autoGet) {
return _autoGet->getView();
} else {
return _autoGetLockFree->getView();
}
}
const NamespaceString& AutoGetCollectionForReadCommandMaybeLockFree::getNss() const {
if (_autoGet) {
return _autoGet->getNss();
} else {
return _autoGetLockFree->getNss();
}
}
OldClientContext::~OldClientContext() {
// If in an interrupt, don't record any stats.
// It is possible to have no lock after saving the lock state and being interrupted while
// waiting to restore.
if (_opCtx->getKillStatus() != ErrorCodes::OK)
return;
invariant(_opCtx->lockState()->isLocked());
auto currentOp = CurOp::get(_opCtx);
Top::get(_opCtx->getClient()->getServiceContext())
.record(_opCtx,
currentOp->getNS(),
currentOp->getLogicalOp(),
_opCtx->lockState()->isWriteLocked() ? Top::LockType::WriteLocked
: Top::LockType::ReadLocked,
_timer.micros(),
currentOp->isCommand(),
currentOp->getReadWriteType());
}
LockMode getLockModeForQuery(OperationContext* opCtx, const boost::optional<NamespaceString>& nss) {
invariant(opCtx);
// Use IX locks for multi-statement transactions; otherwise, use IS locks.
if (opCtx->inMultiDocumentTransaction()) {
uassert(51071,
"Cannot query system.views within a transaction",
!nss || !nss->isSystemDotViews());
return MODE_IX;
}
return MODE_IS;
}
BlockSecondaryReadsDuringBatchApplication_DONT_USE::
BlockSecondaryReadsDuringBatchApplication_DONT_USE(OperationContext* opCtx)
: _opCtx(opCtx) {
auto allowSecondaryReads = &allowSecondaryReadsDuringBatchApplication_DONT_USE(opCtx);
allowSecondaryReads->swap(_originalSettings);
*allowSecondaryReads = false;
}
BlockSecondaryReadsDuringBatchApplication_DONT_USE::
~BlockSecondaryReadsDuringBatchApplication_DONT_USE() {
auto allowSecondaryReads = &allowSecondaryReadsDuringBatchApplication_DONT_USE(_opCtx);
allowSecondaryReads->swap(_originalSettings);
}
template class AutoGetCollectionForReadBase<AutoGetCollection>;
template class AutoGetCollectionForReadCommandBase<AutoGetCollectionForRead>;
template class AutoGetCollectionForReadBase<AutoGetCollectionLockFree>;
template class AutoGetCollectionForReadCommandBase<AutoGetCollectionForReadLockFree>;
} // namespace mongo
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