couch_stats_reader exit with timeout and then the memcached died

The main error log as below:
[error_logger:error,2014-03-06T15:45:05.981,ns_1@192.168.100.106:error_logger<0.6.0>:ale_error_logger_handler:log_msg:76]** Generic server 'couch_stats_reader-contacts' terminating

• • Last message in was refresh_stats
  • When Server state == {state,"contacts",undefined,undefined}
  • Reason for termination ==
  • {timeout,
    Unknown macro: {gen_server,call, [dir_size, {dir_size,"/opt/couchbase/var/lib/couchbase/data/contacts"}]}

    }

[ns_server:info,2014-03-06T15:45:06.037,ns_1@192.168.100.106:ns_config_events<0.276.0>:ns_ports_setup:memcached_force_killer_fn:159]Sent force death command to own memcached:

[ns_server:info,2014-03-06T15:45:06.607,ns_1@192.168.100.106:<0.1512.0>:mc_connection:run_loop:202]mccouch connection was normally closed
[ns_server:info,2014-03-06T15:45:06.609,ns_1@192.168.100.106:<0.16942.0>:mc_connection:run_loop:202]mccouch connection was normally closed
[ns_server:info,2014-03-06T15:45:06.671,ns_1@192.168.100.106:<0.26822.1>:mc_connection:run_loop:202]mccouch connection was normally closed
[error_logger:error,2014-03-06T15:45:06.926,ns_1@192.168.100.106:error_logger<0.6.0>:ale_error_logger_handler:log_report:72]
=========================CRASH REPORT=========================
crasher:
initial call: erlang:apply/2
pid: <0.4224.0>
registered_name: []
exception error: no match of right hand side value

in function mc_client_binary:cmd_binary_vocal_recv/5
in call from mc_client_binary:wait_for_checkpoint_persistence/3
in call from ns_memcached:perform_wait_for_checkpoint_persistence/5
ancestors: ['ns_memcached-usercenter','single_bucket_sup-usercenter',
<0.1487.0>]
messages: []
links: <0.1501.0>,#Port<0.8699>
dictionary: []
trap_exit: false
status: running
heap_size: 121393
stack_size: 24
reductions: 11072
neighbours:

[rebalance:warn,2014-03-06T15:45:06.928,ns_1@192.168.100.106:<0.20193.3>:ebucketmigrator_srv:do_confirm_sent_messages:744]Got error while trying to read close ack:

[ns_server:debug,2014-03-06T15:45:06.046,babysitter_of_ns_1@127.0.0.1:<0.81.0>:ns_port_server:handle_info:80]Sending the following to port: <<"die!\n">>
[ns_server:info,2014-03-06T15:45:06.340,babysitter_of_ns_1@127.0.0.1:<0.81.0>:ns_port_server:log:168]memcached<0.81.0>: 'die!' on stdin. Exiting super-quickly

[error_logger:error,2014-03-06T15:45:06.433,babysitter_of_ns_1@127.0.0.1:error_logger<0.6.0>:ale_error_logger_handler:log_msg:76]** Generic server <0.81.0> terminating

• • Last message in was {#Port<0.2964>,
    Unknown macro: {exit_status,0}

    }

  • When Server state == {state,#Port<0.2964>,memcached,
    {["'die!' on stdin. Exiting super-quickly",