path: root/src/mongo/db/write_concern.cpp

/**
 *    Copyright (C) 2013 10gen Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    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
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    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 GNU Affero General 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,
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 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#include "mongo/platform/basic.h"

#include "mongo/db/write_concern.h"

#include "mongo/base/counter.h"
#include "mongo/bson/util/bson_extract.h"
#include "mongo/db/commands/server_status_metric.h"
#include "mongo/db/service_context.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/repl/optime.h"
#include "mongo/db/repl/replication_coordinator_global.h"
#include "mongo/db/server_options.h"
#include "mongo/db/stats/timer_stats.h"
#include "mongo/db/storage/storage_engine.h"
#include "mongo/db/write_concern_options.h"

namespace mongo {

    using std::string;
    using repl::OpTime;

    static TimerStats gleWtimeStats;
    static ServerStatusMetricField<TimerStats> displayGleLatency("getLastError.wtime",
                                                                 &gleWtimeStats );

    static Counter64 gleWtimeouts;
    static ServerStatusMetricField<Counter64> gleWtimeoutsDisplay("getLastError.wtimeouts",
                                                                  &gleWtimeouts );

    void setupSynchronousCommit(OperationContext* txn) {
        const WriteConcernOptions& writeConcern = txn->getWriteConcern();

        if ( writeConcern.syncMode == WriteConcernOptions::JOURNAL ||
             writeConcern.syncMode == WriteConcernOptions::FSYNC ) {
            txn->recoveryUnit()->goingToWaitUntilDurable();
        }
    }

    namespace {
        // The consensus protocol requires that w: majority implies j: true on all nodes.
        void addJournalSyncForWMajority(WriteConcernOptions* writeConcern) {
            if (repl::getGlobalReplicationCoordinator()->isV1ElectionProtocol()
                && writeConcern->wMode == WriteConcernOptions::kMajority
                && writeConcern->syncMode == WriteConcernOptions::NONE)
            {
                writeConcern->syncMode = WriteConcernOptions::JOURNAL;
            }
        }
    } // namespace

    StatusWith<WriteConcernOptions> extractWriteConcern(const BSONObj& cmdObj) {
        // The default write concern if empty is w : 1
        // Specifying w : 0 is/was allowed, but is interpreted identically to w : 1
        WriteConcernOptions writeConcern = repl::getGlobalReplicationCoordinator()
                ->getGetLastErrorDefault();
        if (writeConcern.wNumNodes == 0 && writeConcern.wMode.empty()) {
            writeConcern.wNumNodes = 1;
        }
        // Upgrade default write concern if necessary.
        addJournalSyncForWMajority(&writeConcern);

        BSONElement writeConcernElement;
        Status wcStatus = bsonExtractTypedField(cmdObj,
                                                "writeConcern",
                                                Object,
                                                &writeConcernElement);
        if (!wcStatus.isOK()) {
            if (wcStatus == ErrorCodes::NoSuchKey) {
                // Return default write concern if no write concern is given.
                return writeConcern;
            }
            return wcStatus;
        }

        BSONObj writeConcernObj = writeConcernElement.Obj();
        // Empty write concern is interpreted to default.
        if (writeConcernObj.isEmpty()) {
            return writeConcern;
        }

        wcStatus = writeConcern.parse(writeConcernObj);
        if (!wcStatus.isOK()) {
            return wcStatus;
        }

        wcStatus = validateWriteConcern(writeConcern);
        if (!wcStatus.isOK()) {
            return wcStatus;
        }

        // Upgrade parsed write concern if necessary.
        addJournalSyncForWMajority(&writeConcern);

        return writeConcern;
    }

    Status validateWriteConcern( const WriteConcernOptions& writeConcern ) {
        const bool isJournalEnabled = getGlobalServiceContext()->getGlobalStorageEngine()->isDurable();

        if ( writeConcern.syncMode == WriteConcernOptions::JOURNAL && !isJournalEnabled ) {
            return Status( ErrorCodes::BadValue,
                           "cannot use 'j' option when a host does not have journaling enabled" );
        }

        const bool isConfigServer = serverGlobalParams.configsvr;
        const repl::ReplicationCoordinator::Mode replMode =
                repl::getGlobalReplicationCoordinator()->getReplicationMode();

        if ( isConfigServer || replMode == repl::ReplicationCoordinator::modeNone ) {

            // Note that config servers can be replicated (have an oplog), but we still don't allow
            // w > 1

            if ( writeConcern.wNumNodes > 1 ) {
                return Status( ErrorCodes::BadValue,
                               string( "cannot use 'w' > 1 " ) +
                               ( isConfigServer ? "on a config server host" :
                                                  "when a host is not replicated" ) );
            }
        }

        if ( replMode != repl::ReplicationCoordinator::modeReplSet &&
                !writeConcern.wMode.empty() &&
                writeConcern.wMode != WriteConcernOptions::kMajority ) {
            return Status( ErrorCodes::BadValue,
                           string( "cannot use non-majority 'w' mode " ) + writeConcern.wMode
                           + " when a host is not a member of a replica set" );
        }

        return Status::OK();
    }

    void WriteConcernResult::appendTo( const WriteConcernOptions& writeConcern,
                                       BSONObjBuilder* result ) const {

        if ( syncMillis >= 0 )
            result->appendNumber( "syncMillis", syncMillis );

        if ( fsyncFiles >= 0 )
            result->appendNumber( "fsyncFiles", fsyncFiles );

        if ( wTime >= 0 ) {
            if ( wTimedOut )
                result->appendNumber( "waited", wTime );
            else
                result->appendNumber( "wtime", wTime );
        }

        if ( wTimedOut )
            result->appendBool( "wtimeout", true );

        if (writtenTo.size()) {
            BSONArrayBuilder hosts(result->subarrayStart("writtenTo"));
            for (size_t i = 0; i < writtenTo.size(); ++i) {
                hosts.append(writtenTo[i].toString());
            }
        }
        else {
            result->appendNull( "writtenTo" );
        }

        if ( err.empty() )
            result->appendNull( "err" );
        else
            result->append( "err", err );

        // *** 2.4 SyncClusterConnection compatibility ***
        // 2.4 expects either fsync'd files, or a "waited" field exist after running an fsync : true
        // GLE, but with journaling we don't actually need to run the fsync (fsync command is
        // preferred in 2.6).  So we add a "waited" field if one doesn't exist.

        if ( writeConcern.syncMode == WriteConcernOptions::FSYNC ) {

            if ( fsyncFiles < 0 && ( wTime < 0 || !wTimedOut ) ) {
                dassert( result->asTempObj()["waited"].eoo() );
                result->appendNumber( "waited", syncMillis );
            }

            dassert( result->asTempObj()["fsyncFiles"].numberInt() > 0 ||
                     !result->asTempObj()["waited"].eoo() );
        }
    }

    Status waitForWriteConcern( OperationContext* txn,
                                const OpTime& replOpTime,
                                WriteConcernResult* result ) {

        const WriteConcernOptions& writeConcern = txn->getWriteConcern();

        // We assume all options have been validated earlier, if not, programming error
        dassert( validateWriteConcern( writeConcern ).isOK() );

        // Next handle blocking on disk

        Timer syncTimer;

        switch( writeConcern.syncMode ) {
        case WriteConcernOptions::NONE:
            break;
        case WriteConcernOptions::FSYNC: {
            StorageEngine* storageEngine = getGlobalServiceContext()->getGlobalStorageEngine();
            if ( !storageEngine->isDurable() ) {
                result->fsyncFiles = storageEngine->flushAllFiles( true );
            }
            else {
                // We only need to commit the journal if we're durable
                txn->recoveryUnit()->waitUntilDurable();
            }
            break;
        }
        case WriteConcernOptions::JOURNAL:
            txn->recoveryUnit()->waitUntilDurable();
            break;
        }

        result->syncMillis = syncTimer.millis();

        // Now wait for replication

        if (replOpTime.isNull()) {
            // no write happened for this client yet
            return Status::OK();
        }

        // needed to avoid incrementing gleWtimeStats SERVER-9005
        if (writeConcern.wNumNodes <= 1 && writeConcern.wMode.empty()) {
            // no desired replication check
            return Status::OK();
        }

        // Now we wait for replication
        // Note that replica set stepdowns and gle mode changes are thrown as errors
        repl::ReplicationCoordinator::StatusAndDuration replStatus =
                repl::getGlobalReplicationCoordinator()->awaitReplication(txn,
                                                                          replOpTime,
                                                                          writeConcern);
        if (replStatus.status == ErrorCodes::WriteConcernFailed) {
            gleWtimeouts.increment();
            result->err = "timeout";
            result->wTimedOut = true;
        }
        // Add stats
        result->writtenTo = repl::getGlobalReplicationCoordinator()->getHostsWrittenTo(replOpTime);
        gleWtimeStats.recordMillis(replStatus.duration.count());
        result->wTime = replStatus.duration.count();

        return replStatus.status;
    }

} // namespace mongo