BSONObj SyncClusterConnection::findOne(const string &ns, Query query, const BSONObj *fieldsToReturn, int queryOptions) {
        
        if ( ns.find( ".$cmd" ) != string::npos ){
            string cmdName = query.obj.firstElement().fieldName();

            int lockType = _lockType( cmdName );

            if ( lockType > 0 ){ // write $cmd
                string errmsg;
                if ( ! prepare( errmsg ) )
                    throw UserException( 13104 , (string)"SyncClusterConnection::insert prepare failed: " + errmsg );
                
                vector<BSONObj> all;
                for ( size_t i=0; i<_conns.size(); i++ ){
                    all.push_back( _conns[i]->findOne( ns , query , 0 , queryOptions ).getOwned() );
                }
                
                _checkLast();
                
                for ( size_t i=0; i<all.size(); i++ ){
                    BSONObj temp = all[i];
                    if ( isOk( temp ) )
                        continue;
                    stringstream ss;
                    ss << "write $cmd failed on a shard: " << temp.jsonString();
                    ss << " " << _conns[i]->toString();
                    throw UserException( 13105 , ss.str() );
                }
                
                return all[0];
            }
        }

        return DBClientBase::findOne( ns , query , fieldsToReturn , queryOptions );
    }
    auto_ptr<DBClientCursor> SyncClusterConnection::query(const string &ns, Query query, int nToReturn, int nToSkip,
            const BSONObj *fieldsToReturn, int queryOptions, int batchSize ) {
        _lastErrors.clear();
        if ( ns.find( ".$cmd" ) != string::npos ) {
            string cmdName = query.obj.firstElementFieldName();
            int lockType = _lockType( cmdName );
            uassert( 13054 , (string)"write $cmd not supported in SyncClusterConnection::query for:" + cmdName , lockType <= 0 );
        }

        return _queryOnActive( ns , query , nToReturn , nToSkip , fieldsToReturn , queryOptions , batchSize );
    }