db=/ssd/db
uri="mongodb://localhost:27017/test?replicaSet=rs"

function clean {
    killall -9 -w mongod
    rm -rf $db
    mkdir -p $db/{r0,r1,r2}
}

function start {
    killall -w mongod
    opts=""
    mongod --dbpath $db/r0 --port 27017 --logpath $db/r0.log --logappend --replSet rs --fork $opts
    mongod --dbpath $db/r1 --port 27117 --logpath $db/r1.log --logappend --replSet rs --fork $opts
    mongod --dbpath $db/r2 --port 27217 --logpath $db/r2.log --logappend --replSet rs --fork $opts
}

function initrs {
    mongo --quiet --eval 'rs.initiate({_id: "rs", members: [{_id: 0, host: "127.0.0.1:27017"}]})'
    mongo --quiet --eval 'rs.add("127.0.0.1:27117")'
    mongo --quiet --eval 'rs.add("127.0.0.1:27217")'
}

function waitrs {
    mongo $uri --quiet --eval "db.version()"
}

function setup {
    mongo $uri --eval '
        db.c.drop()
        db.c.createIndex({_id: 1, x: 1})
        for (var i = 0; i < 10000; i++)
            db.c.insert({_id: i, x: i})
    '
}

function run {
    threads=10
    for i in $(seq $threads); do
        mongo $uri --eval '
            terms = []
            for (var i = 0; i < 10000; i++)
                terms.push({_id: i, x: i})
            print("starting queries")
            for (var i = 0; ; i++) {
                count = db.c.aggregate([{$match: {$or: terms}}]).itcount()
                print(new Date().toISOString(), i, count)
            }
        ' &
    done
    wait
}

clean; start; initrs; waitrs
setup
run

  10 __wt_cond_wait_signal,__wt_readlock,__wt_session_lock_dhandle,__wt_session_get_btree,__wt_session_get_btree_ckpt,__wt_curfile_open,__session_open_cursor_int,__wt_curtable_open,__session_open_cursor_int,__session_open_cursor,mongo::WiredTigerSession::getCursor(std::__cxx11::basic_string<char,,mongo::WiredTigerCursor::WiredTigerCursor(std::__cxx11::basic_string<char,,mongo::WiredTigerRecordStore::getCursor(mongo::OperationContext*,,mongo::Collection::getCursor(mongo::OperationContext*,,mongo::FetchStage::doWork(unsigned,mongo::PlanStage::work(unsigned,mongo::OrStage::doWork(unsigned,mongo::PlanStage::work(unsigned,mongo::PlanStage::work(unsigned,mongo::PlanExecutor::getNextImpl(mongo::Snapshotted<mongo::BSONObj>*,,mongo::PlanExecutor::getNext(mongo::BSONObj*,,mongo::DocumentSourceCursor::loadBatch(),mongo::DocumentSourceCursor::getNext(),mongo::Pipeline::getNext(),mongo::PipelineProxyStage::getNextBson(),mongo::PipelineProxyStage::doWork(unsigned,mongo::PlanStage::work(unsigned,mongo::PlanExecutor::getNextImpl(mongo::Snapshotted<mongo::BSONObj>*,,mongo::PlanExecutor::getNext(mongo::BSONObj*,,mongo::GetMoreCmd::generateBatch(mongo::ClientCursor*,,mongo::GetMoreCmd::runParsed(mongo::OperationContext*,,mongo::GetMoreCmd::run(mongo::OperationContext*,,mongo::Command::run(mongo::OperationContext*,,mongo::Command::execCommand(mongo::OperationContext*,,mongo::runCommands(mongo::OperationContext*,,mongo::assembleResponse(mongo::OperationContext*,,mongo::ServiceEntryPointMongod::_sessionLoop(std::shared_ptr<mongo::transport::Session>,std::_Function_handler<void,mongo::(anonymous,start_thread,clone
   4 __wt_cond_wait_signal,__wt_cond_auto_wait_signal,__wt_cond_auto_wait,__wt_evict_thread_run,__wt_thread_run,start_thread,clone
   1 __wt_cond_wait_signal,__wt_readlock,__wt_session_lock_dhandle,__wt_session_get_btree,__conn_btree_apply_internal,__wt_conn_btree_apply,__checkpoint_apply_all,__checkpoint_prepare,__txn_checkpoint_wrapper,__wt_txn_checkpoint,__session_checkpoint,__ckpt_server,start_thread,clone
   1 __wt_cond_wait_signal,__wt_cond_auto_wait_signal,__wt_cond_auto_wait,__log_wrlsn_server,start_thread,clone
   1 __wt_cond_wait_signal,__wt_cond_auto_wait_signal,__log_server,start_thread,clone
   1 __wt_cond_wait_signal,__sweep_server,start_thread,clone
   1 __wt_cond_wait_signal,__log_file_server,start_thread,clone