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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.
*/
#pragma once
#include "mongo/base/status_with.h"
#include "mongo/db/op_observer.h"
#include "mongo/db/repl/oplog_entry.h"
#include "mongo/db/repl/roll_back_local_operations.h"
#include "mongo/db/repl/rollback.h"
#include "mongo/db/repl/storage_interface.h"
#include "mongo/stdx/functional.h"
namespace mongo {
class OperationContext;
namespace repl {
class OplogInterface;
class ReplicationCoordinator;
class ReplicationProcess;
/**
* Tracks statistics about rollback, and is used to generate a summary about what has occurred.
* Because it is possible for rollback to exit early, fields are initialized to boost::none and are
* populated with actual values during the rollback process.
*/
struct RollbackStats {
/**
* The wall clock time when rollback started.
*/
Date_t startTime;
/**
* The wall clock time when rollback completed, either successfully or unsuccessfully.
*/
Date_t endTime;
/**
* The id number generated for this rollback event.
*/
boost::optional<int> rollbackId;
/**
* The last optime on the branch of history being rolled back.
*/
boost::optional<OpTime> lastLocalOptime;
/**
* The optime of the latest shared oplog entry between this node and the sync source.
*/
boost::optional<OpTime> commonPoint;
/**
* The value of the oplog truncate timestamp. This is the timestamp of the entry immediately
* after the common point on the local oplog (that is, on the branch of history being rolled
* back).
*/
boost::optional<Timestamp> truncateTimestamp;
/**
* The value of the stable timestamp to which rollback recovered.
*/
boost::optional<Timestamp> stableTimestamp;
/**
* The directory containing rollback data files, if any were written.
*/
boost::optional<std::string> rollbackDataFileDirectory;
/**
* The last wall clock time on the branch of history being rolled back, if known.
*/
boost::optional<Date_t> lastLocalWallClockTime;
/**
* The wall clock time at the common point, if known.
*/
boost::optional<Date_t> commonPointWallClockTime;
};
/**
* During steady state replication, it is possible to find the local server in a state where it
* cannot replicate from a sync source. This can happen if the local server has gone offline and
* comes back to find a new primary with an inconsistent set of operations in its oplog from the
* local server. For example:
* F = node that is on the wrong branch of history
* SS = sync source (usually primary)
*
* F : a b c d e f g
* SS : a b c d h
*
* In the example 'e', 'f', and 'g' are getting rolled back, 'h' is what's getting rolled forward.
*
* This class performs 'rollback' via the storage engine's 'recover to a stable timestamp'
* machinery. This class runs synchronously on the caller's thread.
*
* Order of actions:
* 1. Transition to ROLLBACK.
* 2. Await background index completion.
* 3. Find the common point between the local and remote oplogs.
* a. Keep track of what is rolled back to provide a summary to the user and to write
* rollback files.
* b. Maintain a map of how the counts of each collection change during the rollback relative
* to the common point.
* 4. Retrieve the sizes of each collection whose size will change and calculate the
* post-rollback size.
* 5. Increment the Rollback ID (RBID).
* 6. Write rolled back documents to 'Rollback Files'.
* 7. Tell the storage engine to recover to the last stable timestamp.
* 8. Write the oplog entry after the common point as the 'OplogTruncateAfterPoint'.
* 9. Clear drop pending state.
* 10. Call recovery code.
* a. Truncate the oplog at the common point.
* b. Apply all oplog entries to the end of oplog.
* 11. Correct the counts of any collections whose counts changed.
* 12. Reset last optimes from the oplog.
* 13. Trigger the on-rollback op observer.
* 14. Transition to SECONDARY.
*
* If the node crashes while in rollback and the storage engine has not recovered to the last
* stable timestamp yet, then rollback will simply restart against the new sync source upon restart.
* If the node crashes after the storage engine has recovered to the last stable timestamp,
* then the normal startup recovery code will run and finish the rollback process.
*
* If the sync source rolls back while we're searching for a common point, the connection should
* get closed and finding the common point should fail.
*
*/
class RollbackImpl : public Rollback {
public:
/**
* Used to indicate that the files we create with deleted documents are from rollback.
*/
static constexpr auto kRollbackRemoveSaverType = "rollback";
static constexpr auto kRollbackRemoveSaverWhy = "removed";
/**
* A class with functions that get called throughout rollback. These can be overridden to
* instrument this class for diagnostics and testing.
*/
class Listener {
public:
virtual ~Listener() = default;
/**
* Function called after we transition to ROLLBACK.
*/
virtual void onTransitionToRollback() noexcept {}
/**
* Function called after all background index builds have completed.
*/
virtual void onBgIndexesComplete() noexcept {}
/**
* Function called after we find the common point.
*/
virtual void onCommonPointFound(Timestamp commonPoint) noexcept {}
/**
* Function called after a rollback file has been written for each namespace with inserts or
* updates that are being rolled back.
*/
virtual void onRollbackFileWrittenForNamespace(UUID, NamespaceString) noexcept {}
/**
* Function called after we recover to the stable timestamp.
*/
virtual void onRecoverToStableTimestamp(Timestamp stableTimestamp) noexcept {}
/**
* Function called after we set the oplog truncate after point.
*/
virtual void onSetOplogTruncateAfterPoint(Timestamp truncatePoint) noexcept {}
/**
* Function called after we recover from the oplog.
*/
virtual void onRecoverFromOplog() noexcept {}
/**
* Function called after we have triggered the 'onRollback' OpObserver method.
*/
virtual void onRollbackOpObserver(const OpObserver::RollbackObserverInfo& rbInfo) noexcept {
}
};
/**
* Creates a RollbackImpl instance that will run the entire rollback algorithm. This is
* called during steady state replication when we determine that we have to roll back after
* processing the first batch of oplog entries from the sync source.
*/
RollbackImpl(OplogInterface* localOplog,
OplogInterface* remoteOplog,
StorageInterface* storageInterface,
ReplicationProcess* replicationProcess,
ReplicationCoordinator* replicationCoordinator,
Listener* listener);
/**
* Constructs RollbackImpl with a default noop listener.
*/
RollbackImpl(OplogInterface* localOplog,
OplogInterface* remoteOplog,
StorageInterface* storageInterface,
ReplicationProcess* replicationProcess,
ReplicationCoordinator* replicationCoordinator);
virtual ~RollbackImpl();
/**
* Runs the rollback algorithm.
*
* This method transitions to the ROLLBACK state and then performs the steps of the rollback
* process. It is required for this method to transition back to SECONDARY before returning,
* even if rollback did not complete successfully.
*/
Status runRollback(OperationContext* opCtx);
/**
* Cancels all outstanding work.
*/
void shutdown();
/**
* Wrappers to expose private methods for testing.
*/
StatusWith<std::set<NamespaceString>> _namespacesForOp_forTest(const OplogEntry& oplogEntry) {
return _namespacesForOp(oplogEntry);
}
/**
* Returns true if the rollback system should write out data files containing documents that
* will be deleted by rollback.
*/
static bool shouldCreateDataFiles();
/**
* Returns a structure containing all of the documents that would have been written to a
* rollback data file for the namespace represented by 'uuid'.
*
* Only exposed for testing. It is invalid to call this function on a real RollbackImpl.
*/
virtual const std::vector<BSONObj>& docsDeletedForNamespace_forTest(UUID uuid) const& {
MONGO_UNREACHABLE;
}
void docsDeletedForNamespace_forTest(UUID)&& = delete;
protected:
/**
* Returns the document with _id 'id' in the namespace 'nss', or boost::none if that document
* no longer exists in 'nss'. This function is used to write documents to rollback data files,
* and this function will terminate the server if an unexpected error is returned by the storage
* interface.
*
* This function is protected so that subclasses can access this method for test purposes.
*/
boost::optional<BSONObj> _findDocumentById(OperationContext* opCtx,
UUID uuid,
NamespaceString nss,
BSONElement id);
/**
* Writes a rollback file for the namespace 'nss' containing all of the documents whose _ids are
* listed in 'idSet'.
*
* This function is protected so that subclasses can override it for test purposes.
*/
virtual void _writeRollbackFileForNamespace(OperationContext* opCtx,
UUID uuid,
NamespaceString nss,
const SimpleBSONObjUnorderedSet& idSet);
// All member variables are labeled with one of the following codes indicating the
// synchronization rules for accessing them.
//
// (R) Read-only in concurrent operation; no synchronization required.
// (S) Self-synchronizing; access in any way from any context.
// (M) Reads and writes guarded by _mutex.
// (N) Should only ever be accessed by a single thread; no synchronization required.
// A listener that's called at various points throughout rollback.
Listener* _listener; // (R)
private:
/**
* Returns if shutdown was called on this rollback process.
*/
bool _isInShutdown() const;
/**
* Finds the common point between the local and remote oplogs.
*/
StatusWith<RollBackLocalOperations::RollbackCommonPoint> _findCommonPoint(
OperationContext* opCtx);
/**
* Determines whether or not we are trying to roll back too much data. Returns an
* UnrecoverableRollbackError if we have exceeded the limit.
*/
Status _checkAgainstTimeLimit(RollBackLocalOperations::RollbackCommonPoint commonPoint);
/**
* Finds the timestamp of the record after the common point to put into the oplog truncate
* after point.
*/
Timestamp _findTruncateTimestamp(
OperationContext* opCtx, RollBackLocalOperations::RollbackCommonPoint commonPoint) const;
/**
* Uses the ReplicationCoordinator to transition the current member state to ROLLBACK.
* If the transition to ROLLBACK fails, this could mean that we have been elected PRIMARY. In
* this case, we return a NotSecondary error.
*
* 'opCtx' cannot be null.
*/
Status _transitionToRollback(OperationContext* opCtx);
/**
* Waits for any in-progress background index builds to complete. We do this before beginning
* the rollback process to prevent any issues surrounding index builds pausing/resuming around a
* call to 'recoverToStableTimestamp'. It's not clear that an index build, resumed in this way,
* that continues until completion, would be consistent with the collection data. Waiting for
* all background index builds to complete is a conservative approach, to avoid any of these
* potential issues.
*/
Status _awaitBgIndexCompletion(OperationContext* opCtx);
/**
* Recovers to the stable timestamp while holding the global exclusive lock.
* Returns the stable timestamp that the storage engine recovered to.
*/
StatusWith<Timestamp> _recoverToStableTimestamp(OperationContext* opCtx);
/**
* Process a single oplog entry that is getting rolled back and update the necessary rollback
* info structures. This function assumes that oplog entries are processed in descending
* timestamp order (that is, starting from the newest oplog entry, going backwards).
*/
Status _processRollbackOp(const OplogEntry& oplogEntry);
/**
* Iterates through the _countDiff map and retrieves the count of the record store pointed to
* by each UUID. It then saves the post-rollback counts to the _newCounts map.
*/
Status _findRecordStoreCounts(OperationContext* opCtx);
/**
* Sets the record store counts to be the values stored in _newCounts.
*/
void _correctRecordStoreCounts(OperationContext* opCtx);
/**
* Called after we have successfully recovered to the stable timestamp and recovered from the
* oplog. Triggers the replication rollback OpObserver method, notifying other server subsystems
* that a rollback has occurred.
*/
Status _triggerOpObserver(OperationContext* opCtx);
/**
* Transitions the current member state from ROLLBACK to SECONDARY.
* This operation must succeed. Otherwise, we will shut down the server.
*
* 'opCtx' cannot be null.
*/
void _transitionFromRollbackToSecondary(OperationContext* opCtx);
/**
* Returns a set of all collection namespaces affected by the given oplog operation. Does not
* handle 'applyOps' oplog entries, since it assumes their sub operations have already been
* extracted at a higher layer.
*/
StatusWith<std::set<NamespaceString>> _namespacesForOp(const OplogEntry& oplogEntry);
/**
* Persists rollback files to disk for each namespace that contains documents inserted or
* updated after the common point, as these changes will be gone after rollback completes.
* Before each namespace is examined, we check for interrupt and return a non-OK status if
* shutdown is in progress.
*
* This function causes the server to terminate if an error occurs while fetching documents from
* disk or while writing documents to the rollback file. It must be called before marking the
* oplog truncate point, and before the storage engine recovers to the stable timestamp.
*/
Status _writeRollbackFiles(OperationContext* opCtx);
/**
* Logs a summary of what has occurred so far during rollback to the server log.
*/
void _summarizeRollback(OperationContext* opCtx) const;
/**
* Aligns the drop pending reaper's state with the catalog.
*/
void _resetDropPendingState(OperationContext* opCtx);
// Guards access to member variables.
mutable stdx::mutex _mutex; // (S)
// Set to true when RollbackImpl should shut down.
bool _inShutdown = false; // (M)
// This is used to read oplog entries from the local oplog that will be rolled back.
OplogInterface* const _localOplog; // (R)
// This is used to read oplog entries from the remote oplog to find the common point.
OplogInterface* const _remoteOplog; // (R)
// The StorageInterface associated with this Rollback instance. Used to execute operations
// at the storage layer e.g. recovering to a timestamp.
StorageInterface* _storageInterface; // (R)
// The ReplicationProcess associated with this Rollback instance. Used to update and persist
// various pieces of replication state related to the rollback process.
ReplicationProcess* _replicationProcess; // (R)
// This is used to read and update global replication settings. This includes:
// - update transition member states;
ReplicationCoordinator* const _replicationCoordinator; // (R)
// Contains information about the rollback that will be passed along to the rollback OpObserver
// method.
OpObserver::RollbackObserverInfo _observerInfo = {}; // (N)
// Holds information about this rollback event.
RollbackStats _rollbackStats; // (N)
// Maintains a count of the difference between the count of the record store pointed to by the
// UUID before recover to a stable timestamp is called and the count after we recover from the
// oplog. This only must keep track of inserts and deletes. Rolling back drops is just a rename
// and rolling back creates means that the UUID does not exist post rollback.
stdx::unordered_map<UUID, long long, UUID::Hash> _countDiffs; // (N)
// Maintains the count of the record store pointed to by the UUID after we recover from the
// oplog.
stdx::unordered_map<UUID, long long, UUID::Hash> _newCounts; // (N)
};
} // namespace repl
} // namespace mongo
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