Пример #1
0
    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;
    }
Пример #2
0
    /**
     * 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) {
        log() << "Running query on new system: " << q.query.toString() << endl;

        // 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);

        // 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: Document why we do this.
        // TODO: do this when we can pass in our own parsed query
        //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;

        // We turn on auto-yielding for the runner here, so we must register it with the active
        // runners list in ClientCursor.
        ClientCursor::registerRunner(runner.get());
        runner->setYieldPolicy(Runner::YIELD_AUTO);

        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 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 && enoughForExplain(pq, numResults)) {
                break;
            }
            else if (!supportsGetMore && (enough(pq, numResults)
                                          || bb.len() >= MaxBytesToReturnToClientAtOnce)) {
                break;
            }
            else if (enoughForFirstBatch(pq, 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;
            }
        }

        // If we cache the runner later, we want to deregister it as it receives notifications
        // anyway by virtue of being cached.
        //
        // If we don't cache the runner later, we are deleting it, so it must be deregistered.
        //
        // So, no matter what, deregister the runner.
        ClientCursor::deregisterRunner(runner.get());

        // Why save a dead runner?
        if (Runner::RUNNER_DEAD == state) { saveClientCursor = false; }

        // 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.
        //
        // TODO: If we're tailable we want to save the client cursor.  Make sure we do this later.
        //if (pq.hasOption(QueryOption_CursorTailable) && pq.getNumToReturn() != 1) { ... }

        // TODO(greg): This will go away soon.
        if (!shardingState.getVersion(pq.ns()).isWriteCompatibleWith(shardingVersionAtStart)) {
            // if the version changed during the query we might be missing some data and its safe to
            // send this as mongos can resend at this point
            throw SendStaleConfigException(pq.ns(), "version changed during initial query",
                                           shardingVersionAtStart,
                                           shardingState.getVersion(pq.ns()));
        }

        long long ccId = 0;
        if (saveClientCursor) {
            // We won't use the runner until it's getMore'd.
            runner->saveState();

            // Allocate a new ClientCursor.  We don't have to worry about leaking it as it's
            // inserted into a global map by its ctor.
            ClientCursor* cc = new ClientCursor(runner.get(), cq->getParsed().getOptions(),
                                                cq->getParsed().getFilter());
            ccId = cc->cursorid();

            log() << "caching runner with cursorid " << ccId << endl;

            // ClientCursor takes ownership of runner.  Release to make sure it's not deleted.
            runner.release();

            // TODO document
            if (pq.hasOption(QueryOption_OplogReplay) && !slaveReadTill.isNull()) {
                cc->slaveReadTill(slaveReadTill);
            }

            // TODO document
            if (pq.hasOption(QueryOption_Exhaust)) {
                curop.debug().exhaust = true;
            }

            // Set attributes for getMore.
            cc->setCollMetadata(collMetadata);
            cc->setPos(numResults);

            // If the query had a time limit, remaining time is "rolled over" to the cursor (for
            // use by future getmore ops).
            cc->setLeftoverMaxTimeMicros(curop.getRemainingMaxTimeMicros());
        }

        // Add the results from the query into the output buffer.
        result.appendData(bb.buf(), bb.len());
        bb.decouple();

        // Fill out the output buffer's header.
        QueryResult* qr = static_cast<QueryResult*>(result.header());
        qr->cursorId = ccId;
        curop.debug().cursorid = (0 == ccId ? -1 : ccId);
        qr->setResultFlagsToOk();
        qr->setOperation(opReply);
        qr->startingFrom = 0;
        qr->nReturned = numResults;
        // TODO: nscanned is bogus.
        // curop.debug().nscanned = ( cursor ? cursor->nscanned() : 0LL );
        curop.debug().ntoskip = pq.getSkip();
        curop.debug().nreturned = numResults;

        // curop.debug().exhaust is set above.
        return curop.debug().exhaust ? pq.ns() : "";
    }
Пример #3
0
    /**
     * 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;

        // TODO: Document.
        // TODO: do this when we can pass in our own parsed query
        //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());
            // 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.
            // TODO: There may be special handling required for tailable cursors?
            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;
                }
            }

            if (Runner::RUNNER_DEAD == state || Runner::RUNNER_EOF == state) {
                log() << "getMore(): runner with id " << cursorid << " EOF/DEAD, state = "
                      << static_cast<int>(state) << endl;
                // TODO: If the cursor is tailable we don't kill it if it's eof.
                ccPin.free();
                // cc is now invalid, as is the runner
                cursorid = 0;
                cc = NULL;
            }
            else {
                // Continue caching the ClientCursor.
                cc->incPos(numResults);
                runner->saveState();

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

                exhaust = (queryOptions & QueryOption_Exhaust);

                // If the getmore had a time limit, remaining time is "rolled over" back to the
                // cursor (for use by future getmore ops).
                cc->setLeftoverMaxTimeMicros( curop.getRemainingMaxTimeMicros() );
            }
        }

        QueryResult* qr = reinterpret_cast<QueryResult*>(bb.buf());
        qr->len = bb.len();
        qr->setOperation(opReply);
        qr->_resultFlags() = resultFlags;
        qr->cursorId = cursorid;
        qr->startingFrom = startingResult;
        qr->nReturned = numResults;
        bb.decouple();
        return qr;
    }
Пример #4
0
    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.
        const IndexCatalog* catalog = _collection->getIndexCatalog();

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

        // This may not be valid always.  See SERVER-12397.
        const BtreeBasedAccessMethod* accessMethod =
            static_cast<const BtreeBasedAccessMethod*>(catalog->getIndex(idDesc));

        // 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;
        }

        _nscanned++;

        // Set out parameters and note that we're done w/lookup.
        if (NULL == objOut) {
            // No object requested - nothing to do.
        }
        else if (hasIDProjection(_query.get())) {
            // Covered query on _id field only.
            // Set object to search key.
            // Search key is retrieved from the canonical query at
            // construction and always contains the _id field name.
            // It is possible to construct the ID hack runner with just the collection
            // and the key object (which could be {"": my_obj_id}) but _query would be null
            // in that case and the query would never be seen as covered.
            *objOut = _key.getOwned();
        }
        else {
            invariant(!hasIDProjection(_query.get()));

            // Fetch object from storage.
            Record* record = loc.rec();

            _nscannedObjects++;

            // 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(_collection->ns().ns())) {
                CollectionMetadataPtr m = shardingState.getCollectionMetadata(_collection->ns().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;
                    }
                }
            }
        }

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

        return Runner::RUNNER_ADVANCED;
    }
Пример #5
0
    /**
     * 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);

            // If the getmore had a time limit, remaining time is "rolled over" back to the
            // cursor (for use by future getmore ops).
            cc->setLeftoverMaxTimeMicros( curop.getRemainingMaxTimeMicros() );
        }

        QueryResult* qr = reinterpret_cast<QueryResult*>(bb.buf());
        qr->len = bb.len();
        qr->setOperation(opReply);
        qr->_resultFlags() = resultFlags;
        qr->cursorId = cursorid;
        qr->startingFrom = startingResult;
        qr->nReturned = numResults;
        bb.decouple();
        return qr;
    }
Пример #6
0
    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;
                    cc = 0;
                    break;
                }

                MatchDetails details;
                if ( cc->fields && cc->fields->getArrayOpType() == Projection::ARRAY_OP_POSITIONAL ) {
                    // field projection specified, and contains an array operator
                    details.requestElemMatchKey();
                }

                // in some cases (clone collection) there won't be a matcher
                if ( !c->currentMatches( &details ) ) {
                }
                else if ( metadata && !metadata->keyBelongsToMe( extractKey(c, keyPattern ) ) ) {
                    LOG(2) << "cursor skipping document in un-owned chunk: " << c->current()
                               << endl;
                }
                else {
                    if( c->getsetdup(c->currLoc()) ) {
                        //out() << "  but it's a dup \n";
                    }
                    else {
                        last = c->currLoc();
                        n++;

                        // Fill out the fields requested by the query.
                        const Projection::KeyOnly *keyFieldsOnly = c->keyFieldsOnly();
                        if ( keyFieldsOnly ) {
                            fillQueryResultFromObj( b, 0, keyFieldsOnly->hydrate(
                            c->currKey() ), &details );
                        }
                        else {
                            DiskLoc loc = c->currLoc();
                            fillQueryResultFromObj( b, cc->fields.get(), c->current(), &details,
                                    ( ( cc->pq.get() && cc->pq->showDiskLoc() ) ? &loc : 0 ) );
                        }

                        if ( ( ntoreturn && n >= ntoreturn ) || b.len() > MaxBytesToReturnToClientAtOnce ) {
                            c->advance();
                            cc->incPos( n );
                            break;
                        }
                    }
                }
                c->advance();

                if ( ! cc->yieldSometimes( ( c->ok() && c->keyFieldsOnly() ) ?
                                          ClientCursor::DontNeed : ClientCursor::WillNeed ) ) {
                    ClientCursor::erase(cursorid);
                    cursorid = 0;
                    cc = 0;
                    break;
                }
            }
            
            if ( cc ) {
                if ( c->supportYields() ) {
                    ClientCursor::YieldData data;
                    verify( cc->prepareToYield( data ) );
                }
                else {
                    cc->c()->noteLocation();
                }
                cc->storeOpForSlave( last );
                exhaust = cc->queryOptions() & QueryOption_Exhaust;

                // If the getmore had a time limit, remaining time is "rolled over" back to the
                // cursor (for use by future getmore ops).
                cc->setLeftoverMaxTimeMicros( curop.getRemainingMaxTimeMicros() );
            }
        }

        QueryResult *qr = (QueryResult *) b.buf();
        qr->len = b.len();
        qr->setOperation(opReply);
        qr->_resultFlags() = resultFlags;
        qr->cursorId = cursorid;
        qr->startingFrom = start;
        qr->nReturned = n;
        b.decouple();

        return qr;
    }