C++ CollectionMetadataPtr类代码示例

    /**
     * Cleans up one range of orphaned data starting from a range that overlaps or starts at
     * 'startingFromKey'.  If empty, startingFromKey is the minimum key of the sharded range.
     *
     * @return CleanupResult_Continue and 'stoppedAtKey' if orphaned range was found and cleaned
     * @return CleanupResult_Done if no orphaned ranges remain
     * @return CleanupResult_Error and 'errMsg' if an error occurred
     *
     * If the collection is not sharded, returns CleanupResult_Done.
     */
    CleanupResult cleanupOrphanedData( OperationContext* txn,
                                       const NamespaceString& ns,
                                       const BSONObj& startingFromKeyConst,
                                       const WriteConcernOptions& secondaryThrottle,
                                       BSONObj* stoppedAtKey,
                                       string* errMsg ) {

        BSONObj startingFromKey = startingFromKeyConst;

        CollectionMetadataPtr metadata = shardingState.getCollectionMetadata( ns.toString() );
        if ( !metadata || metadata->getKeyPattern().isEmpty() ) {

            warning() << "skipping orphaned data cleanup for " << ns.toString()
                      << ", collection is not sharded" << endl;

            return CleanupResult_Done;
        }

        BSONObj keyPattern = metadata->getKeyPattern();
        if ( !startingFromKey.isEmpty() ) {
            if ( !metadata->isValidKey( startingFromKey ) ) {

                *errMsg = stream() << "could not cleanup orphaned data, start key "
                                   << startingFromKey
                                   << " does not match shard key pattern " << keyPattern;

                warning() << *errMsg << endl;
                return CleanupResult_Error;
            }
        }
        else {
            startingFromKey = metadata->getMinKey();
        }

        KeyRange orphanRange;
        if ( !metadata->getNextOrphanRange( startingFromKey, &orphanRange ) ) {

            LOG( 1 ) << "orphaned data cleanup requested for " << ns.toString()
                     << " starting from " << startingFromKey
                     << ", no orphan ranges remain" << endl;

            return CleanupResult_Done;
        }
        *stoppedAtKey = orphanRange.maxKey;

        // We're done with this metadata now, no matter what happens
        metadata.reset();

        LOG( 1 ) << "orphaned data cleanup requested for " << ns.toString()
                 << " starting from " << startingFromKey
                 << ", removing next orphan range"
                 << " [" << orphanRange.minKey << "," << orphanRange.maxKey << ")"
                 << endl;

        // Metadata snapshot may be stale now, but deleter checks metadata again in write lock
        // before delete.
        if ( !getDeleter()->deleteNow( txn,
                                       ns.toString(),
                                       orphanRange.minKey,
                                       orphanRange.maxKey,
                                       keyPattern,
                                       secondaryThrottle,
                                       errMsg ) ) {

            warning() << *errMsg << endl;
            return CleanupResult_Error;
        }

        return CleanupResult_Continue;
    }

/**
 * For a given query, get a runner.  The runner could be a SingleSolutionRunner, a
 * CachedQueryRunner, or a MultiPlanRunner, depending on the cache/query solver/etc.
 */
Status getRunner(Collection* collection, CanonicalQuery* rawCanonicalQuery,
                 Runner** out, size_t plannerOptions) {

    verify(rawCanonicalQuery);
    auto_ptr<CanonicalQuery> canonicalQuery(rawCanonicalQuery);

    // This can happen as we're called by internal clients as well.
    if (NULL == collection) {
        const string& ns = canonicalQuery->ns();
        *out = new EOFRunner(canonicalQuery.release(), ns);
        return Status::OK();
    }

    // If we have an _id index we can use the idhack runner.
    if (canUseIDHack(*canonicalQuery) && collection->getIndexCatalog()->findIdIndex()) {
        *out = new IDHackRunner(collection, canonicalQuery.release());
        return Status::OK();
    }

    // If it's not NULL, we may have indices.  Access the catalog and fill out IndexEntry(s)
    QueryPlannerParams plannerParams;

    IndexCatalog::IndexIterator ii = collection->getIndexCatalog()->getIndexIterator(false);
    while (ii.more()) {
        const IndexDescriptor* desc = ii.next();
        plannerParams.indices.push_back(IndexEntry(desc->keyPattern(),
                                        desc->isMultikey(),
                                        desc->isSparse(),
                                        desc->indexName(),
                                        desc->infoObj()));
    }

    // If query supports admin hint, filter params.indices by indexes in query settings.
    QuerySettings* querySettings = collection->infoCache()->getQuerySettings();
    AllowedIndices* allowedIndicesRaw;

    // Filter index catalog if admin hint is specified for query.
    // Also, signal to planner that application hint should be ignored.
    if (querySettings->getAllowedIndices(*canonicalQuery, &allowedIndicesRaw)) {
        boost::scoped_ptr<AllowedIndices> allowedIndices(allowedIndicesRaw);
        filterAllowedIndexEntries(*allowedIndices, &plannerParams.indices);
        plannerParams.adminHintApplied = true;
    }

    // Tailable: If the query requests tailable the collection must be capped.
    if (canonicalQuery->getParsed().hasOption(QueryOption_CursorTailable)) {
        if (!collection->isCapped()) {
            return Status(ErrorCodes::BadValue,
                          "error processing query: " + canonicalQuery->toString() +
                          " tailable cursor requested on non capped collection");
        }

        // If a sort is specified it must be equal to expectedSort.
        const BSONObj expectedSort = BSON("$natural" << 1);
        const BSONObj& actualSort = canonicalQuery->getParsed().getSort();
        if (!actualSort.isEmpty() && !(actualSort == expectedSort)) {
            return Status(ErrorCodes::BadValue,
                          "error processing query: " + canonicalQuery->toString() +
                          " invalid sort specified for tailable cursor: "
                          + actualSort.toString());
        }
    }

    // Process the planning options.
    plannerParams.options = plannerOptions;
    if (storageGlobalParams.noTableScan) {
        const string& ns = canonicalQuery->ns();
        // There are certain cases where we ignore this restriction:
        bool ignore = canonicalQuery->getQueryObj().isEmpty()
                      || (string::npos != ns.find(".system."))
                      || (0 == ns.find("local."));
        if (!ignore) {
            plannerParams.options |= QueryPlannerParams::NO_TABLE_SCAN;
        }
    }

    if (!(plannerParams.options & QueryPlannerParams::NO_TABLE_SCAN)) {
        plannerParams.options |= QueryPlannerParams::INCLUDE_COLLSCAN;
    }

    // If the caller wants a shard filter, make sure we're actually sharded.
    if (plannerParams.options & QueryPlannerParams::INCLUDE_SHARD_FILTER) {
        CollectionMetadataPtr collMetadata =
            shardingState.getCollectionMetadata(canonicalQuery->ns());

        if (collMetadata) {
            plannerParams.shardKey = collMetadata->getKeyPattern();
        }
        else {
            // If there's no metadata don't bother w/the shard filter since we won't know what
            // the key pattern is anyway...
            plannerParams.options &= ~QueryPlannerParams::INCLUDE_SHARD_FILTER;
        }
    }

    // Try to look up a cached solution for the query.
//.........这里部分代码省略.........

bool mergeChunks(OperationContext* txn,
                 const NamespaceString& nss,
                 const BSONObj& minKey,
                 const BSONObj& maxKey,
                 const OID& epoch,
                 string* errMsg) {
    //
    // Get sharding state up-to-date
    //

    ConnectionString configLoc = ConnectionString::parse(shardingState.getConfigServer(), *errMsg);
    if (!configLoc.isValid()) {
        warning() << *errMsg << endl;
        return false;
    }

    //
    // Get the distributed lock
    //

    string whyMessage = stream() << "merging chunks in " << nss.ns() << " from " << minKey << " to "
                                 << maxKey;
    auto scopedDistLock = grid.catalogManager()->getDistLockManager()->lock(nss.ns(), whyMessage);

    if (!scopedDistLock.isOK()) {
        *errMsg = stream() << "could not acquire collection lock for " << nss.ns()
                           << " to merge chunks in [" << minKey << "," << maxKey << ")"
                           << causedBy(scopedDistLock.getStatus());

        warning() << *errMsg << endl;
        return false;
    }

    //
    // We now have the collection lock, refresh metadata to latest version and sanity check
    //

    ChunkVersion shardVersion;
    Status status = shardingState.refreshMetadataNow(txn, nss.ns(), &shardVersion);

    if (!status.isOK()) {
        *errMsg = str::stream() << "could not merge chunks, failed to refresh metadata for "
                                << nss.ns() << causedBy(status.reason());

        warning() << *errMsg << endl;
        return false;
    }

    if (epoch.isSet() && shardVersion.epoch() != epoch) {
        *errMsg = stream() << "could not merge chunks, collection " << nss.ns() << " has changed"
                           << " since merge was sent"
                           << "(sent epoch : " << epoch.toString()
                           << ", current epoch : " << shardVersion.epoch().toString() << ")";

        warning() << *errMsg << endl;
        return false;
    }

    CollectionMetadataPtr metadata = shardingState.getCollectionMetadata(nss.ns());

    if (!metadata || metadata->getKeyPattern().isEmpty()) {
        *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                           << " is not sharded";

        warning() << *errMsg << endl;
        return false;
    }

    dassert(metadata->getShardVersion().equals(shardVersion));

    if (!metadata->isValidKey(minKey) || !metadata->isValidKey(maxKey)) {
        *errMsg = stream() << "could not merge chunks, the range " << rangeToString(minKey, maxKey)
                           << " is not valid"
                           << " for collection " << nss.ns() << " with key pattern "
                           << metadata->getKeyPattern();

        warning() << *errMsg << endl;
        return false;
    }

    //
    // Get merged chunk information
    //

    ChunkVersion mergeVersion = metadata->getCollVersion();
    mergeVersion.incMinor();

    std::vector<ChunkType> chunksToMerge;

    ChunkType itChunk;
    itChunk.setMin(minKey);
    itChunk.setMax(minKey);
    itChunk.setNS(nss.ns());
    itChunk.setShard(shardingState.getShardName());

    while (itChunk.getMax().woCompare(maxKey) < 0 &&
           metadata->getNextChunk(itChunk.getMax(), &itChunk)) {
        chunksToMerge.push_back(itChunk);
    }

//.........这里部分代码省略.........

    /**
     * This is called by db/ops/query.cpp.  This is the entry point for answering a query.
     */
    string newRunQuery(Message& m, QueryMessage& q, CurOp& curop, Message &result) {
        // This is a read lock.
        Client::ReadContext ctx(q.ns, dbpath);

        // Parse, canonicalize, plan, transcribe, and get a runner.
        Runner* rawRunner;
        Status status = getRunner(q, &rawRunner);
        if (!status.isOK()) {
            uasserted(17007, "Couldn't process query " + q.query.toString()
                         + " why: " + status.reason());
        }
        verify(NULL != rawRunner);
        auto_ptr<Runner> runner(rawRunner);

        // We freak out later if this changes before we're done with the query.
        const ChunkVersion shardingVersionAtStart = shardingState.getVersion(q.ns);

        // We use this a lot below.
        const ParsedQuery& pq = runner->getQuery().getParsed();

        // TODO: Document why we do this.
        replVerifyReadsOk(&pq);

        // If this exists, the collection is sharded.
        // If it doesn't exist, we can assume we're not sharded.
        // If we're sharded, we might encounter data that is not consistent with our sharding state.
        // We must ignore this data.
        CollectionMetadataPtr collMetadata;
        if (!shardingState.needCollectionMetadata(pq.ns())) {
            collMetadata = CollectionMetadataPtr();
        }
        else {
            collMetadata = shardingState.getCollectionMetadata(pq.ns());
        }

        // Run the query.
        BufBuilder bb(32768);
        bb.skip(sizeof(QueryResult));

        // How many results have we obtained from the runner?
        int numResults = 0;

        // If we're replaying the oplog, we save the last time that we read.
        OpTime slaveReadTill;

        // Do we save the Runner in a ClientCursor for getMore calls later?
        bool saveClientCursor = false;

        BSONObj obj;
        // TODO: Differentiate EOF from error.
        while (runner->getNext(&obj)) {
            // If we're sharded make sure that we don't return any data that hasn't been migrated
            // off of our shared yet.
            if (collMetadata) {
                // This information can change if we yield and as such we must make sure to re-fetch
                // it if we yield.
                KeyPattern kp(collMetadata->getKeyPattern());
                // This performs excessive BSONObj creation but that's OK for now.
                if (!collMetadata->keyBelongsToMe(kp.extractSingleKey(obj))) { continue; }
            }

            // Add result to output buffer.
            bb.appendBuf((void*)obj.objdata(), obj.objsize());

            // Count the result.
            ++numResults;

            // Possibly note slave's position in the oplog.
            if (pq.hasOption(QueryOption_OplogReplay)) {
                BSONElement e = obj["ts"];
                if (Date == e.type() || Timestamp == e.type()) {
                    slaveReadTill = e._opTime();
                }
            }

            // TODO: only one type of 2d search doesn't support this.  We need a way to pull it out
            // of CanonicalQuery. :(
            const bool supportsGetMore = true;
            const bool isExplain = pq.isExplain();
            if (isExplain && pq.enoughForExplain(numResults)) {
                break;
            }
            else if (!supportsGetMore && (pq.enough(numResults)
                                          || bb.len() >= MaxBytesToReturnToClientAtOnce)) {
                break;
            }
            else if (pq.enoughForFirstBatch(numResults, bb.len())) {
                // If only one result requested assume it's a findOne() and don't save the cursor.
                if (pq.wantMore() && 1 != pq.getNumToReturn()) {
                    saveClientCursor = true;
                }
                break;
            }
        }

        // TODO: Stage creation can set tailable depending on what's in the parsed query.  We have
        // the full parsed query available during planning...set it there.
//.........这里部分代码省略.........

    Runner::RunnerState IDHackRunner::getNext(BSONObj* objOut, DiskLoc* dlOut) {
        if (_killed) { return Runner::RUNNER_DEAD; }
        if (_done) { return Runner::RUNNER_EOF; }

        // Use the index catalog to get the id index.
        IndexCatalog* catalog = _collection->getIndexCatalog();

        // Find the index we use.
        const IndexDescriptor* idDesc = catalog->findIdIndex();
        if (NULL == idDesc) {
            _done = true;
            return Runner::RUNNER_EOF;
        }

        BtreeBasedAccessMethod* accessMethod = catalog->getBtreeBasedIndex( idDesc );

        BSONObj key = _query->getQueryObj()["_id"].wrap();

        // Look up the key by going directly to the Btree.
        DiskLoc loc = accessMethod->findSingle( key );

        _done = true;

        // Key not found.
        if (loc.isNull()) {
            return Runner::RUNNER_EOF;
        }

        // Set out parameters and note that we're done w/lookup.
        if (NULL != objOut) {
            Record* record = loc.rec();

            // If the record isn't in memory...
            if (!Record::likelyInPhysicalMemory(record->dataNoThrowing())) {
                // And we're allowed to yield ourselves...
                if (Runner::YIELD_AUTO == _policy) {
                    // Note what we're yielding to fetch so that we don't crash if the loc is
                    // deleted during a yield.
                    _locFetching = loc;
                    // Yield.  TODO: Do we want to bother yielding if micros < 0?
                    int micros = ClientCursor::suggestYieldMicros();
                    ClientCursor::staticYield(micros, "", record);
                    // This can happen when we're yielded for various reasons (e.g. db/idx dropped).
                    if (_killed) {
                        return Runner::RUNNER_DEAD;
                    }
                }
            }

            // Either the data was in memory or we paged it in.
            *objOut = loc.obj();

            // If we're sharded make sure the key belongs to us.  We need the object to do this.
            if (shardingState.needCollectionMetadata(_query->ns())) {
                CollectionMetadataPtr m = shardingState.getCollectionMetadata(_query->ns());
                if (m) {
                    KeyPattern kp(m->getKeyPattern());
                    if (!m->keyBelongsToMe( kp.extractSingleKey(*objOut))) {
                        // We have something with a matching _id but it doesn't belong to me.
                        return Runner::RUNNER_EOF;
                    }
                }
            }

            // If there is a projection...
            if (NULL != _query->getProj()) {
                // Create something to execute it.
                auto_ptr<ProjectionExec> projExec(new ProjectionExec(_query->getParsed().getProj(),
                                                                     _query->root()));
                projExec->transform(*objOut, objOut);
            }
        }

        // Return the DiskLoc if the caller wants it.
        if (NULL != dlOut) {
            *dlOut = loc;
        }

        return Runner::RUNNER_ADVANCED;
    }

    /**
     * Also called by db/ops/query.cpp.  This is the new getMore entry point.
     */
    QueryResult* newGetMore(const char* ns, int ntoreturn, long long cursorid, CurOp& curop,
                            int pass, bool& exhaust, bool* isCursorAuthorized) {
        exhaust = false;
        int bufSize = 512 + sizeof(QueryResult) + MaxBytesToReturnToClientAtOnce;

        BufBuilder bb(bufSize);
        bb.skip(sizeof(QueryResult));

        // This is a read lock.  TODO: There is a cursor flag for not needing this.  Do we care?
        Client::ReadContext ctx(ns);

        // TODO: Document.
        replVerifyReadsOk();

        ClientCursorPin ccPin(cursorid);
        ClientCursor* cc = ccPin.c();

        // These are set in the QueryResult msg we return.
        int resultFlags = ResultFlag_AwaitCapable;

        int numResults = 0;
        int startingResult = 0;

        if (NULL == cc) {
            cursorid = 0;
            resultFlags = ResultFlag_CursorNotFound;
        }
        else {
            // Quote: check for spoofing of the ns such that it does not match the one originally
            // there for the cursor
            uassert(17011, "auth error", str::equals(ns, cc->ns().c_str()));
            *isCursorAuthorized = true;

            // TODO: fail point?

            // If the operation that spawned this cursor had a time limit set, apply leftover
            // time to this getmore.
            curop.setMaxTimeMicros(cc->getLeftoverMaxTimeMicros());
            // TODO:
            // curop.debug().query = BSONForQuery
            // curop.setQuery(curop.debug().query);

            // TODO: What is pass?
            if (0 == pass) { cc->updateSlaveLocation(curop); }

            CollectionMetadataPtr collMetadata = cc->getCollMetadata();

            // If we're replaying the oplog, we save the last time that we read.
            OpTime slaveReadTill;

            startingResult = cc->pos();

            Runner* runner = cc->getRunner();
            const ParsedQuery& pq = runner->getQuery().getParsed();

            // Get results out of the runner.
            // TODO: There may be special handling required for tailable cursors?
            runner->restoreState();
            BSONObj obj;
            // TODO: Differentiate EOF from error.
            while (runner->getNext(&obj)) {
                // If we're sharded make sure that we don't return any data that hasn't been
                // migrated off of our shard yet.
                if (collMetadata) {
                    KeyPattern kp(collMetadata->getKeyPattern());
                    if (!collMetadata->keyBelongsToMe(kp.extractSingleKey(obj))) { continue; }
                }

                // Add result to output buffer.
                bb.appendBuf((void*)obj.objdata(), obj.objsize());

                // Count the result.
                ++numResults;

                // Possibly note slave's position in the oplog.
                if (pq.hasOption(QueryOption_OplogReplay)) {
                    BSONElement e = obj["ts"];
                    if (Date == e.type() || Timestamp == e.type()) {
                        slaveReadTill = e._opTime();
                    }
                }

                if ((numResults && numResults >= ntoreturn)
                    || bb.len() > MaxBytesToReturnToClientAtOnce) {
                    break;
                }
            }

            cc->incPos(numResults);
            runner->saveState();

            // Possibly note slave's position in the oplog.
            if (pq.hasOption(QueryOption_OplogReplay) && !slaveReadTill.isNull()) {
                cc->slaveReadTill(slaveReadTill);
            }

            exhaust = pq.hasOption(QueryOption_Exhaust);
//.........这里部分代码省略.........

    /**
     * This is called by db/ops/query.cpp.  This is the entry point for answering a query.
     */
    string newRunQuery(Message& m, QueryMessage& q, CurOp& curop, Message &result) {
        // This is a read lock.
        Client::ReadContext ctx(q.ns, dbpath);

        // Parse, canonicalize, plan, transcribe, and get a runner.
        Runner* rawRunner;
        CanonicalQuery* cq;
        Status status = getRunner(q, &rawRunner, &cq);
        if (!status.isOK()) {
            uasserted(17007, "Couldn't process query " + q.query.toString()
                         + " why: " + status.reason());
        }
        verify(NULL != rawRunner);
        auto_ptr<Runner> runner(rawRunner);

        log() << "Running query on new system: " << cq->toString();

        // We freak out later if this changes before we're done with the query.
        const ChunkVersion shardingVersionAtStart = shardingState.getVersion(q.ns);

        // We use this a lot below.
        const LiteParsedQuery& pq = cq->getParsed();

        // TODO: Remove when impl'd
        if (pq.hasOption(QueryOption_OplogReplay)) {
            warning() << "haven't implemented findingstartcursor yet\n";
        }

        // Handle query option $maxTimeMS (not used with commands).
        curop.setMaxTimeMicros(static_cast<unsigned long long>(pq.getMaxTimeMS()) * 1000);
        killCurrentOp.checkForInterrupt(); // May trigger maxTimeAlwaysTimeOut fail point.

        // uassert if we are not on a primary, and not a secondary with SlaveOk query parameter set.
        replVerifyReadsOk(&pq);

        // If this exists, the collection is sharded.
        // If it doesn't exist, we can assume we're not sharded.
        // If we're sharded, we might encounter data that is not consistent with our sharding state.
        // We must ignore this data.
        CollectionMetadataPtr collMetadata;
        if (!shardingState.needCollectionMetadata(pq.ns())) {
            collMetadata = CollectionMetadataPtr();
        }
        else {
            collMetadata = shardingState.getCollectionMetadata(pq.ns());
        }

        // Run the query.
        // bb is used to hold query results
        // this buffer should contain either requested documents per query or
        // explain information, but not both
        BufBuilder bb(32768);
        bb.skip(sizeof(QueryResult));

        // How many results have we obtained from the runner?
        int numResults = 0;

        // If we're replaying the oplog, we save the last time that we read.
        OpTime slaveReadTill;

        // Do we save the Runner in a ClientCursor for getMore calls later?
        bool saveClientCursor = false;

        // We turn on auto-yielding for the runner here.  The runner registers itself with the
        // active runners list in ClientCursor.
        ClientCursor::registerRunner(runner.get());
        runner->setYieldPolicy(Runner::YIELD_AUTO);
        auto_ptr<DeregisterEvenIfUnderlyingCodeThrows> safety(
            new DeregisterEvenIfUnderlyingCodeThrows(runner.get()));

        BSONObj obj;
        Runner::RunnerState state;

        // set this outside loop. we will need to use this both within loop and when deciding
        // to fill in explain information
        const bool isExplain = pq.isExplain();

        while (Runner::RUNNER_ADVANCED == (state = runner->getNext(&obj, NULL))) {
            // If we're sharded make sure that we don't return any data that hasn't been migrated
            // off of our shared yet.
            if (collMetadata) {
                // This information can change if we yield and as such we must make sure to re-fetch
                // it if we yield.
                KeyPattern kp(collMetadata->getKeyPattern());
                // This performs excessive BSONObj creation but that's OK for now.
                if (!collMetadata->keyBelongsToMe(kp.extractSingleKey(obj))) { continue; }
            }

            // Add result to output buffer. This is unnecessary if explain info is requested
            if (!isExplain) {
                bb.appendBuf((void*)obj.objdata(), obj.objsize());
            }

            // Count the result.
            ++numResults;

            // Possibly note slave's position in the oplog.
//.........这里部分代码省略.........

    /**
     * Also called by db/ops/query.cpp.  This is the new getMore entry point.
     */
    QueryResult* newGetMore(const char* ns, int ntoreturn, long long cursorid, CurOp& curop,
                            int pass, bool& exhaust, bool* isCursorAuthorized) {
        exhaust = false;
        int bufSize = 512 + sizeof(QueryResult) + MaxBytesToReturnToClientAtOnce;

        BufBuilder bb(bufSize);
        bb.skip(sizeof(QueryResult));

        // This is a read lock.  TODO: There is a cursor flag for not needing this.  Do we care?
        Client::ReadContext ctx(ns);

        //log() << "running getMore in new system, cursorid " << cursorid << endl;

        // This checks to make sure the operation is allowed on a replicated node.  Since we are not
        // passing in a query object (necessary to check SlaveOK query option), the only state where
        // reads are allowed is PRIMARY (or master in master/slave).  This function uasserts if
        // reads are not okay.
        replVerifyReadsOk();

        // A pin performs a CC lookup and if there is a CC, increments the CC's pin value so it
        // doesn't time out.  Also informs ClientCursor that there is somebody actively holding the
        // CC, so don't delete it.
        ClientCursorPin ccPin(cursorid);
        ClientCursor* cc = ccPin.c();

        // These are set in the QueryResult msg we return.
        int resultFlags = ResultFlag_AwaitCapable;

        int numResults = 0;
        int startingResult = 0;

        if (NULL == cc) {
            cursorid = 0;
            resultFlags = ResultFlag_CursorNotFound;
        }
        else {
            // Quote: check for spoofing of the ns such that it does not match the one originally
            // there for the cursor
            uassert(17011, "auth error", str::equals(ns, cc->ns().c_str()));
            *isCursorAuthorized = true;

            // TODO: fail point?

            // If the operation that spawned this cursor had a time limit set, apply leftover
            // time to this getmore.
            curop.setMaxTimeMicros(cc->getLeftoverMaxTimeMicros());
            killCurrentOp.checkForInterrupt(); // May trigger maxTimeAlwaysTimeOut fail point.

            // TODO:
            // curop.debug().query = BSONForQuery
            // curop.setQuery(curop.debug().query);

            // TODO: What is pass?
            if (0 == pass) { cc->updateSlaveLocation(curop); }

            CollectionMetadataPtr collMetadata = cc->getCollMetadata();

            // If we're replaying the oplog, we save the last time that we read.
            OpTime slaveReadTill;

            // What number result are we starting at?  Used to fill out the reply.
            startingResult = cc->pos();

            // What gives us results.
            Runner* runner = cc->getRunner();
            const int queryOptions = cc->queryOptions();

            // Get results out of the runner.
            runner->restoreState();

            BSONObj obj;
            Runner::RunnerState state;
            while (Runner::RUNNER_ADVANCED == (state = runner->getNext(&obj, NULL))) {
                // If we're sharded make sure that we don't return any data that hasn't been
                // migrated off of our shard yet.
                if (collMetadata) {
                    KeyPattern kp(collMetadata->getKeyPattern());
                    if (!collMetadata->keyBelongsToMe(kp.extractSingleKey(obj))) { continue; }
                }

                // Add result to output buffer.
                bb.appendBuf((void*)obj.objdata(), obj.objsize());

                // Count the result.
                ++numResults;

                // Possibly note slave's position in the oplog.
                if (queryOptions & QueryOption_OplogReplay) {
                    BSONElement e = obj["ts"];
                    if (Date == e.type() || Timestamp == e.type()) {
                        slaveReadTill = e._opTime();
                    }
                }

                if ((numResults && numResults >= ntoreturn)
                    || bb.len() > MaxBytesToReturnToClientAtOnce) {
                    break;
//.........这里部分代码省略.........

    /**
     * For a given query, get a runner.  The runner could be a SingleSolutionRunner, a
     * CachedQueryRunner, or a MultiPlanRunner, depending on the cache/query solver/etc.
     */
    Status getRunner(CanonicalQuery* rawCanonicalQuery, Runner** out, size_t plannerOptions) {
        verify(rawCanonicalQuery);
        auto_ptr<CanonicalQuery> canonicalQuery(rawCanonicalQuery);

        // Try to look up a cached solution for the query.
        // TODO: Can the cache have negative data about a solution?
        PlanCache* localCache = PlanCache::get(canonicalQuery->ns());
        if (NULL != localCache) {
            CachedSolution* cs = localCache->get(*canonicalQuery);
            if (NULL != cs) {
                // We have a cached solution.  Hand the canonical query and cached solution off to
                // the cached plan runner, which takes ownership of both.
                WorkingSet* ws;
                PlanStage* root;
                verify(StageBuilder::build(*cs->solution, &root, &ws));
                *out = new CachedPlanRunner(canonicalQuery.release(), cs, root, ws);
                return Status::OK();
            }
        }

        // No entry in cache for the query.  We have to solve the query ourself.

        // Get the indices that we could possibly use.
        Database* db = cc().database();
        verify( db );
        Collection* collection = db->getCollection( canonicalQuery->ns() );

        // This can happen as we're called by internal clients as well.
        if (NULL == collection) {
            const string& ns = canonicalQuery->ns();
            *out = new EOFRunner(canonicalQuery.release(), ns);
            return Status::OK();
        }

        // If we have an _id index we can use the idhack runner.
        if (canUseIDHack(*canonicalQuery) && collection->getIndexCatalog()->findIdIndex()) {
            *out = new IDHackRunner(collection, canonicalQuery.release());
            return Status::OK();
        }

        // If it's not NULL, we may have indices.  Access the catalog and fill out IndexEntry(s)
        QueryPlannerParams plannerParams;
        for (int i = 0; i < collection->getIndexCatalog()->numIndexesReady(); ++i) {
            IndexDescriptor* desc = collection->getIndexCatalog()->getDescriptor( i );
            plannerParams.indices.push_back(IndexEntry(desc->keyPattern(),
                                                       desc->isMultikey(),
                                                       desc->isSparse(),
                                                       desc->indexName()));
        }

        // Tailable: If the query requests tailable the collection must be capped.
        if (canonicalQuery->getParsed().hasOption(QueryOption_CursorTailable)) {
            if (!collection->isCapped()) {
                return Status(ErrorCodes::BadValue,
                              "tailable cursor requested on non capped collection");
            }

            // If a sort is specified it must be equal to expectedSort.
            const BSONObj expectedSort = BSON("$natural" << 1);
            const BSONObj& actualSort = canonicalQuery->getParsed().getSort();
            if (!actualSort.isEmpty() && !(actualSort == expectedSort)) {
                return Status(ErrorCodes::BadValue,
                              "invalid sort specified for tailable cursor: "
                              + actualSort.toString());
            }
        }

        // Process the planning options.
        plannerParams.options = plannerOptions;
        if (storageGlobalParams.noTableScan) {
            const string& ns = canonicalQuery->ns();
            // There are certain cases where we ignore this restriction:
            bool ignore = canonicalQuery->getQueryObj().isEmpty()
                          || (string::npos != ns.find(".system."))
                          || (0 == ns.find("local."));
            if (!ignore) {
                plannerParams.options |= QueryPlannerParams::NO_TABLE_SCAN;
            }
        }

        if (!(plannerParams.options & QueryPlannerParams::NO_TABLE_SCAN)) {
            plannerParams.options |= QueryPlannerParams::INCLUDE_COLLSCAN;
        }

        // If the caller wants a shard filter, make sure we're actually sharded.
        if (plannerParams.options & QueryPlannerParams::INCLUDE_SHARD_FILTER) {
            CollectionMetadataPtr collMetadata = shardingState.getCollectionMetadata(canonicalQuery->ns());
            if (collMetadata) {
                plannerParams.shardKey = collMetadata->getKeyPattern();
            }
            else {
                // If there's no metadata don't bother w/the shard filter since we won't know what
                // the key pattern is anyway...
                plannerParams.options &= ~QueryPlannerParams::INCLUDE_SHARD_FILTER;
            }
        }
//.........这里部分代码省略.........

    QueryResult* processGetMore(const char* ns,
                                int ntoreturn,
                                long long cursorid,
                                CurOp& curop,
                                int pass,
                                bool& exhaust,
                                bool* isCursorAuthorized ) {
        if (isNewQueryFrameworkEnabled()) {
            return newGetMore(ns, ntoreturn, cursorid, curop, pass, exhaust, isCursorAuthorized);
        }

        exhaust = false;

        int bufSize = 512 + sizeof( QueryResult ) + MaxBytesToReturnToClientAtOnce;

        BufBuilder b( bufSize );
        b.skip(sizeof(QueryResult));
        int resultFlags = ResultFlag_AwaitCapable;
        int start = 0;
        int n = 0;

        scoped_ptr<Client::ReadContext> ctx(new Client::ReadContext(ns));
        // call this readlocked so state can't change
        replVerifyReadsOk();

        ClientCursorPin p(cursorid);
        ClientCursor *cc = p.c();

        if ( unlikely(!cc) ) {
            LOGSOME << "getMore: cursorid not found " << ns << " " << cursorid << endl;
            cursorid = 0;
            resultFlags = ResultFlag_CursorNotFound;
        }
        else {
            // Some internal users create a ClientCursor with a Runner.  Don't crash if this
            // happens.  Instead, hand them off to the new framework.
            if (NULL != cc->getRunner()) {
                p.release();
                return newGetMore(ns, ntoreturn, cursorid, curop, pass, exhaust, isCursorAuthorized);
            }

            // check for spoofing of the ns such that it does not match the one originally there for the cursor
            uassert(14833, "auth error", str::equals(ns, cc->ns().c_str()));

            *isCursorAuthorized = true;

            // This must be done after auth check to ensure proper cleanup.
            uassert(16951, "failing getmore due to set failpoint",
                    !MONGO_FAIL_POINT(getMoreError));

            // If the operation that spawned this cursor had a time limit set, apply leftover
            // time to this getmore.
            curop.setMaxTimeMicros( cc->getLeftoverMaxTimeMicros() );

            if ( pass == 0 )
                cc->updateSlaveLocation( curop );

            int queryOptions = cc->queryOptions();
            
            curop.debug().query = cc->query();
            curop.setQuery( cc->query() );

            start = cc->pos();
            Cursor *c = cc->c();

            if (!c->requiresLock()) {
                // make sure it won't be destroyed under us
                fassert(16952, !c->shouldDestroyOnNSDeletion());
                fassert(16953, !c->supportYields());
                ctx.reset(); // unlocks
            }

            c->recoverFromYield();
            DiskLoc last;

            // This metadata may be stale, but it's the state of chunking when the cursor was
            // created.
            CollectionMetadataPtr metadata = cc->getCollMetadata();
            KeyPattern keyPattern( metadata ? metadata->getKeyPattern() : BSONObj() );

            while ( 1 ) {
                if ( !c->ok() ) {
                    if ( c->tailable() ) {
                        // when a tailable cursor hits "EOF", ok() goes false, and current() is
                        // null.  however advance() can still be retries as a reactivation attempt.
                        // when there is new data, it will return true.  that's what we are doing
                        // here.
                        if ( c->advance() )
                            continue;

                        if( n == 0 && (queryOptions & QueryOption_AwaitData) && pass < 1000 ) {
                            return 0;
                        }

                        break;
                    }
                    p.release();
                    bool ok = ClientCursor::erase(cursorid);
                    verify(ok);
                    cursorid = 0;
//.........这里部分代码省略.........