path: root/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.h

/**
 *    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 <functional>
#include <list>
#include <memory>
#include <string>

#include <boost/filesystem/path.hpp>
#include <wiredtiger.h>

#include "mongo/bson/ordering.h"
#include "mongo/bson/timestamp.h"
#include "mongo/db/concurrency/d_concurrency.h"
#include "mongo/db/storage/kv/kv_engine.h"
#include "mongo/db/storage/storage_engine.h"
#include "mongo/db/storage/wiredtiger/wiredtiger_oplog_manager.h"
#include "mongo/db/storage/wiredtiger/wiredtiger_session_cache.h"
#include "mongo/db/storage/wiredtiger/wiredtiger_util.h"
#include "mongo/platform/mutex.h"
#include "mongo/util/elapsed_tracker.h"

namespace mongo {

class ClockSource;
class JournalListener;
class WiredTigerRecordStore;
class WiredTigerSessionCache;
class WiredTigerSizeStorer;
class WiredTigerEngineRuntimeConfigParameter;

struct WiredTigerFileVersion {
    // MongoDB 4.4+ will not open on datafiles left behind by 4.2.5 and earlier. MongoDB 4.4
    // shutting down in FCV 4.2 will leave data files that 4.2.6+ will understand
    // (IS_44_FCV_42). MongoDB 4.2.x always writes out IS_42.
    enum class StartupVersion { IS_42, IS_44_FCV_42, IS_44_FCV_44 };

    StartupVersion _startupVersion;
    bool shouldDowngrade(bool readOnly, bool repairMode, bool hasRecoveryTimestamp);
    std::string getDowngradeString();
};

struct WiredTigerBackup {
    WT_CURSOR* cursor = nullptr;
    WT_CURSOR* dupCursor = nullptr;
    std::set<std::string> logFilePathsSeenByExtendBackupCursor;
    std::set<std::string> logFilePathsSeenByGetNextBatch;

    // 'wtBackupCursorMutex' provides concurrency control between beginNonBlockingBackup(),
    // endNonBlockingBackup(), and getNextBatch() because we stream the output of the backup cursor.
    Mutex wtBackupCursorMutex = MONGO_MAKE_LATCH("WiredTigerKVEngine::wtBackupCursorMutex");

    // 'wtBackupDupCursorMutex' provides concurrency control between getNextBatch() and
    // extendBackupCursor() because WiredTiger only allows one duplicate cursor to be open at a
    // time. extendBackupCursor() blocks on condition variable 'wtBackupDupCursorCV' if a duplicate
    // cursor is already open.
    Mutex wtBackupDupCursorMutex = MONGO_MAKE_LATCH("WiredTigerKVEngine::wtBackupDupCursorMutex");
    stdx::condition_variable wtBackupDupCursorCV;
};

class WiredTigerKVEngine final : public KVEngine {
public:
    static StringData kTableUriPrefix;

    WiredTigerKVEngine(const std::string& canonicalName,
                       const std::string& path,
                       ClockSource* cs,
                       const std::string& extraOpenOptions,
                       size_t cacheSizeMB,
                       size_t maxHistoryFileSizeMB,
                       bool durable,
                       bool ephemeral,
                       bool repair,
                       bool readOnly);

    ~WiredTigerKVEngine();

    void startAsyncThreads() override;

    void setRecordStoreExtraOptions(const std::string& options);
    void setSortedDataInterfaceExtraOptions(const std::string& options);

    bool supportsDocLocking() const override;

    bool supportsDirectoryPerDB() const override;

    /**
     * WiredTiger supports checkpoints when it isn't running in memory.
     */
    bool supportsCheckpoints() const override {
        return !isEphemeral();
    }

    bool isDurable() const override {
        return _durable;
    }

    bool isEphemeral() const override {
        return _ephemeral;
    }

    void setOldestActiveTransactionTimestampCallback(
        StorageEngine::OldestActiveTransactionTimestampCallback callback) override;

    RecoveryUnit* newRecoveryUnit() override;

    Status createRecordStore(OperationContext* opCtx,
                             StringData ns,
                             StringData ident,
                             const CollectionOptions& options) override {
        return createGroupedRecordStore(opCtx, ns, ident, options, KVPrefix::kNotPrefixed);
    }

    std::unique_ptr<RecordStore> getRecordStore(OperationContext* opCtx,
                                                StringData ns,
                                                StringData ident,
                                                const CollectionOptions& options) override {
        return getGroupedRecordStore(opCtx, ns, ident, options, KVPrefix::kNotPrefixed);
    }

    std::unique_ptr<RecordStore> makeTemporaryRecordStore(OperationContext* opCtx,
                                                          StringData ident) override;

    Status createSortedDataInterface(OperationContext* opCtx,
                                     const CollectionOptions& collOptions,
                                     StringData ident,
                                     const IndexDescriptor* desc) override {
        return createGroupedSortedDataInterface(
            opCtx, collOptions, ident, desc, KVPrefix::kNotPrefixed);
    }

    std::unique_ptr<SortedDataInterface> getSortedDataInterface(
        OperationContext* opCtx, StringData ident, const IndexDescriptor* desc) override {
        return getGroupedSortedDataInterface(opCtx, ident, desc, KVPrefix::kNotPrefixed);
    }

    Status createGroupedRecordStore(OperationContext* opCtx,
                                    StringData ns,
                                    StringData ident,
                                    const CollectionOptions& options,
                                    KVPrefix prefix) override;

    std::unique_ptr<RecordStore> getGroupedRecordStore(OperationContext* opCtx,
                                                       StringData ns,
                                                       StringData ident,
                                                       const CollectionOptions& options,
                                                       KVPrefix prefix) override;

    Status createGroupedSortedDataInterface(OperationContext* opCtx,
                                            const CollectionOptions& collOptions,
                                            StringData ident,
                                            const IndexDescriptor* desc,
                                            KVPrefix prefix) override;

    std::unique_ptr<SortedDataInterface> getGroupedSortedDataInterface(OperationContext* opCtx,
                                                                       StringData ident,
                                                                       const IndexDescriptor* desc,
                                                                       KVPrefix prefix) override;

    Status dropIdent(OperationContext* opCtx, RecoveryUnit* ru, StringData ident) override;

    Status okToRename(OperationContext* opCtx,
                      StringData fromNS,
                      StringData toNS,
                      StringData ident,
                      const RecordStore* originalRecordStore) const override;

    void flushAllFiles(OperationContext* opCtx, bool callerHoldsReadLock) override;

    Status beginBackup(OperationContext* opCtx) override;

    void endBackup(OperationContext* opCtx) override;

    Status disableIncrementalBackup(OperationContext* opCtx) override;

    StatusWith<std::unique_ptr<StorageEngine::StreamingCursor>> beginNonBlockingBackup(
        OperationContext* opCtx, const StorageEngine::BackupOptions& options) override;

    void endNonBlockingBackup(OperationContext* opCtx) override;

    virtual StatusWith<std::vector<std::string>> extendBackupCursor(
        OperationContext* opCtx) override;

    int64_t getIdentSize(OperationContext* opCtx, StringData ident) override;

    Status repairIdent(OperationContext* opCtx, StringData ident) override;

    Status recoverOrphanedIdent(OperationContext* opCtx,
                                const NamespaceString& nss,
                                StringData ident,
                                const CollectionOptions& options) override;

    bool hasIdent(OperationContext* opCtx, StringData ident) const override;

    std::vector<std::string> getAllIdents(OperationContext* opCtx) const override;

    void cleanShutdown() override;

    SnapshotManager* getSnapshotManager() const final {
        return &_sessionCache->snapshotManager();
    }

    void setJournalListener(JournalListener* jl) final;

    void setStableTimestamp(Timestamp stableTimestamp, bool force) override;

    void setInitialDataTimestamp(Timestamp initialDataTimestamp) override;

    void setOldestTimestampFromStable() override;

    /**
     * Sets the oldest timestamp for which the storage engine must maintain snapshot history
     * through. If force is true, oldest will be set to the given input value, unmodified, even if
     * it is backwards in time from the last oldest timestamp (accomodating initial sync).
     */
    void setOldestTimestamp(Timestamp newOldestTimestamp, bool force) override;

    bool supportsRecoverToStableTimestamp() const override;

    bool supportsRecoveryTimestamp() const override;

    StatusWith<Timestamp> recoverToStableTimestamp(OperationContext* opCtx) override;

    boost::optional<Timestamp> getRecoveryTimestamp() const override;

    /**
     * Returns a stable timestamp value that is guaranteed to exist on recoverToStableTimestamp.
     * Replication recovery will not need to replay documents with an earlier time.
     *
     * Only returns a stable timestamp when it has advanced to >= the initial data timestamp.
     * Replication recoverable rollback is unsafe when stable < initial during repl initial sync due
     * to initial sync's cloning phase without timestamps.
     *
     * For the persisted mode of this engine, further guarantees a stable timestamp value that is at
     * or before the last checkpoint. Everything before this value is guaranteed to be persisted on
     * disk. This supports replication recovery on restart.
     */
    boost::optional<Timestamp> getLastStableRecoveryTimestamp() const override;

    Timestamp getAllDurableTimestamp() const override;

    Timestamp getOldestOpenReadTimestamp() const override;

    bool supportsReadConcernSnapshot() const final override;

    bool supportsOplogStones() const final override;

    bool isCacheUnderPressure(OperationContext* opCtx) const override;

    bool supportsReadConcernMajority() const final;

    // wiredtiger specific
    // Calls WT_CONNECTION::reconfigure on the underlying WT_CONNECTION
    // held by this class
    int reconfigure(const char* str);

    WT_CONNECTION* getConnection() {
        return _conn;
    }
    void dropSomeQueuedIdents();
    std::list<WiredTigerCachedCursor> filterCursorsWithQueuedDrops(
        std::list<WiredTigerCachedCursor>* cache);
    bool haveDropsQueued() const;

    void syncSizeInfo(bool sync) const;

    /*
     * The oplog manager is always accessible, but this method will start the background thread to
     * control oplog entry visibility for reads.
     *
     * On mongod, the background thread will be started when the oplog record store is created, and
     * stopped when the oplog record store is destroyed. For unit tests, the background thread may
     * be started and stopped multiple times as tests create and destroy the oplog record store.
     */
    void startOplogManager(OperationContext* opCtx, WiredTigerRecordStore* oplogRecordStore);
    void haltOplogManager();

    /*
     * Always returns a non-nil pointer. However, the WiredTigerOplogManager may not have been
     * initialized and its background refreshing thread may not be running.
     *
     * A caller that wants to get the oplog read timestamp, or call
     * `waitForAllEarlierOplogWritesToBeVisible`, is advised to first see if the oplog manager is
     * running with a call to `isRunning`.
     *
     * A caller that simply wants to call `triggerOplogVisibilityUpdate` may do so without concern.
     */
    WiredTigerOplogManager* getOplogManager() const {
        return _oplogManager.get();
    }

    static void appendGlobalStats(BSONObjBuilder& b);

    Timestamp getStableTimestamp() const override;
    Timestamp getOldestTimestamp() const override;
    Timestamp getCheckpointTimestamp() const override;

    Timestamp getInitialDataTimestamp() const;

    /**
     * Returns the data file path associated with an ident on disk. Returns boost::none if the data
     * file can not be found. This will attempt to locate a file even if the storage engine's own
     * metadata is not aware of the ident. This is intented for database repair purposes only.
     */
    boost::optional<boost::filesystem::path> getDataFilePathForIdent(StringData ident) const;

    /**
     * Returns the minimum possible Timestamp value in the oplog that replication may need for
     * recovery in the event of a rollback. This value depends on the timestamp passed to
     * `setStableTimestamp` and on the set of active MongoDB transactions. Returns an error if it
     * times out querying the active transctions.
     */
    StatusWith<Timestamp> getOplogNeededForRollback() const;

    /**
     * Returns the minimum possible Timestamp value in the oplog that replication may need for
     * recovery in the event of a crash. This value gets updated every time a checkpoint is
     * completed. This value is typically a lagged version of what's needed for rollback.
     *
     * Returns boost::none when called on an ephemeral database.
     */
    boost::optional<Timestamp> getOplogNeededForCrashRecovery() const final;

    /**
     * Returns oplog that may not be truncated. This method is a function of oplog needed for
     * rollback and oplog needed for crash recovery. This method considers different states the
     * storage engine can be running in, such as running in in-memory mode.
     *
     * This method returning Timestamp::min() implies no oplog should be truncated and
     * Timestamp::max() means oplog can be truncated freely based on user oplog size
     * configuration.
     */
    Timestamp getPinnedOplog() const;

    ClockSource* getClockSource() const {
        return _clockSource;
    }

private:
    class WiredTigerSessionSweeper;
    class WiredTigerCheckpointThread;

    /**
     * Opens a connection on the WiredTiger database 'path' with the configuration 'wtOpenConfig'.
     * Only returns when successful. Intializes both '_conn' and '_fileVersion'.
     *
     * If corruption is detected and _inRepairMode is 'true', attempts to salvage the WiredTiger
     * metadata.
     */
    void _openWiredTiger(const std::string& path, const std::string& wtOpenConfig);

    Status _salvageIfNeeded(const char* uri);
    void _ensureIdentPath(StringData ident);

    /**
     * Recreates a WiredTiger ident from the provided URI by dropping and recreating the ident.
     * This moves aside the existing data file, if one exists, with an added ".corrupt" suffix.
     *
     * Returns DataModifiedByRepair if the rebuild was successful, and any other error on failure.
     * This will never return Status::OK().
     */
    Status _rebuildIdent(WT_SESSION* session, const char* uri);

    bool _hasUri(WT_SESSION* session, const std::string& uri) const;

    std::string _uri(StringData ident) const;

    /**
     * Uses the 'stableTimestamp', the 'minSnapshotHistoryWindowInSeconds' setting and the
     * current _oldestTimestamp to calculate what the new oldest_timestamp should be, in order to
     * maintain a window of available snapshots on the storage engine from oldest to stable
     * timestamp.
     *
     * If the returned Timestamp isNull(), oldest_timestamp should not be moved forward.
     */
    Timestamp _calculateHistoryLagFromStableTimestamp(Timestamp stableTimestamp);

    /**
     * Checks whether rollback to a timestamp can occur, enforcing a contract of use between the
     * storage engine and replication.
     *
     * It is required that setInitialDataTimestamp has been called with a valid value other than
     * kAllowUnstableCheckpointsSentinel by the time a node is fully set up -- initial sync
     * complete, replica set initialized, etc. Else, this fasserts.
     * Furthermore, rollback cannot go back farther in the past than the initial data timestamp, so
     * the stable timestamp must be greater than initial data timestamp for a valid rollback. This
     * function will return false if that is not true.
     */
    bool _canRecoverToStableTimestamp() const;

    std::uint64_t _getCheckpointTimestamp() const;

    mutable Mutex _oldestActiveTransactionTimestampCallbackMutex =
        MONGO_MAKE_LATCH("::_oldestActiveTransactionTimestampCallbackMutex");
    StorageEngine::OldestActiveTransactionTimestampCallback
        _oldestActiveTransactionTimestampCallback;

    WT_CONNECTION* _conn;
    WiredTigerFileVersion _fileVersion;
    WiredTigerEventHandler _eventHandler;
    std::unique_ptr<WiredTigerSessionCache> _sessionCache;
    ClockSource* const _clockSource;

    // Mutex to protect use of _oplogManagerCount by this instance of KV engine.
    mutable Mutex _oplogManagerMutex = MONGO_MAKE_LATCH("::_oplogManagerMutex");
    std::size_t _oplogManagerCount = 0;
    std::unique_ptr<WiredTigerOplogManager> _oplogManager;

    std::string _canonicalName;
    std::string _path;
    std::string _wtOpenConfig;

    std::unique_ptr<WiredTigerSizeStorer> _sizeStorer;
    std::string _sizeStorerUri;
    mutable ElapsedTracker _sizeStorerSyncTracker;

    bool _durable;
    bool _ephemeral;  // whether we are using the in-memory mode of the WT engine
    const bool _inRepairMode;
    bool _readOnly;

    // If _keepDataHistory is true, then the storage engine keeps all history after the stable
    // timestamp, and WiredTigerKVEngine is responsible for advancing the oldest timestamp. If
    // _keepDataHistory is false (i.e. majority reads are disabled), then we only keep history after
    // the "no holes point", and WiredTigerOplogManager is responsible for advancing the oldest
    // timestamp.
    const bool _keepDataHistory = true;

    std::unique_ptr<WiredTigerSessionSweeper> _sessionSweeper;
    std::unique_ptr<WiredTigerCheckpointThread> _checkpointThread;

    std::string _rsOptions;
    std::string _indexOptions;

    mutable Mutex _dropAllQueuesMutex = MONGO_MAKE_LATCH("WiredTigerKVEngine::_dropAllQueuesMutex");
    mutable Mutex _identToDropMutex = MONGO_MAKE_LATCH("WiredTigerKVEngine::_identToDropMutex");
    std::list<std::string> _identToDrop;

    mutable Date_t _previousCheckedDropsQueued;

    std::unique_ptr<WiredTigerSession> _backupSession;
    WiredTigerBackup _wtBackup;

    mutable Mutex _oplogPinnedByBackupMutex =
        MONGO_MAKE_LATCH("WiredTigerKVEngine::_oplogPinnedByBackupMutex");
    boost::optional<Timestamp> _oplogPinnedByBackup;
    Timestamp _recoveryTimestamp;

    // Tracks the stable and oldest timestamps we've set on the storage engine.
    AtomicWord<std::uint64_t> _oldestTimestamp;
    AtomicWord<std::uint64_t> _stableTimestamp;

    // Timestamp of data at startup. Used internally to advise checkpointing and recovery to a
    // timestamp. Provided by replication layer because WT does not persist timestamps.
    AtomicWord<std::uint64_t> _initialDataTimestamp;

    std::unique_ptr<WiredTigerEngineRuntimeConfigParameter> _runTimeConfigParam;

    mutable Mutex _highestDurableTimestampMutex =
        MONGO_MAKE_LATCH("WiredTigerKVEngine::_highestDurableTimestampMutex");
    mutable unsigned long long _highestSeenDurableTimestamp = StorageEngine::kMinimumTimestamp;
};
}  // namespace mongo