RAND()/ENCODE() lack of concurrency

./rand-test.lua --threads=140 --db-driver=mysql --mysql-user=root --mysql-db=information_schema  --mysql-host=10.61.210.91  --histogram  run

{

    "errors":    0,

    "events": 2423705,

    "latency_avg": 0.0005767600,

    "latency_max": 0.0049197530,

    "latency_min": 0.0001138200,

    "latency_pct": 0.0005972396,

    "latency_sum": 1397.8983984280,

    "other":    0,

    "reads": 2423705,

    "reconnects":    0,

    "threads_running":    0,

    "time_interval": 10.0254642940,

    "time_total": 10.0225462340,

    "writes":    0

Samples: 715K of event 'cycles', Event count (approx.): 109823327400

  Overhead  Command  Shared Object       Symbol

+    9.85%  mysqld   mysqld              [.] SQL_CRYPT::init                                                                  ◆

+    9.42%  mysqld   mysqld              [.] my_rnd                                                                           ▒

+    8.05%  mysqld   [kernel.vmlinux]    [k] ctx_sched_in        

-    9.85%  mysqld   mysqld              [.] SQL_CRYPT::init                                                                  ◆

     __clone                                                                                                                  ▒

     start_thread                                                                                                             ▒

     handle_one_connection                                                                                                    ▒

     do_handle_one_connection                                                                                                 ▒

     do_command                                                                                                               ▒

     dispatch_command                                                                                                         ▒

     mysql_stmt_execute_common                                                                                                ▒

     Prepared_statement::execute_loop                                                                                         ▒

     Prepared_statement::execute                                                                                              ▒

     mysql_execute_command                                                                                                    ▒

     execute_sqlcom_select                                                                                                    ▒

     handle_select                                                                                                            ▒

     mysql_select                                                                                                             ▒

     JOIN::exec                                                                                                               ▒

     JOIN::exec_inner                                                                                                         ▒

     select_send::send_data                                                                                                   ▒

     Protocol::send_result_set_row                                                                                            ▒

     Item::send                                                                                                               ▒

     Type_handler_string_result::Item_send                                                                                    ▒

     Type_handler::Item_send_str                                                                                              ▒

   - Item_func_encode::val_str                                                                                                ▒

      - 9.82% Item_func_encode::seed                                                                                          ▒

           SQL_CRYPT::init     

       │         int idx= (uint) (my_rnd(&rand)*255.0);

  2.71 │ 70:   mr      r3,r30

  0.02 │     → bl      my_rnd

  2.45 │       nop

       │         char a= decode_buff[idx];

       │         decode_buff[idx]= decode_buff[i];

  4.57 │       lbzu    r8,1(r31)

       │         int idx= (uint) (my_rnd(&rand)*255.0);

  0.00 │       lfd     f0,0(r28)

       │       for (i=0 ; i<= 255 ; i++)

 19.45 │       cmpld   cr7,r31,r27

       │         int idx= (uint) (my_rnd(&rand)*255.0);

  0.05 │       fmul    f1,f1,f0

  0.00 │       fctiwuz f1,f1

 18.98 │       mffprwz r9,f1

  0.03 │       extsw   r9,r9

       │         char a= decode_buff[idx];

       │       add     r9,r30,r9

 23.24 │       lbz     r10,64(r9)

       │         decode_buff[idx]= decode_buff[i];

  2.10 │       stb     r8,64(r9)

       │         decode_buff[+i]=a;

  0.03 │       stb     r10,0(r31)

       │       for (i=0 ; i<= 255 ; i++)

       │     ↑ bne     cr7,70

       │       }

       │       for (i=0 ; i <= 255 ; i++)

  0.02 │       li      r9,256

       │       li      r10,0

-    9.42%  mysqld   mysqld              [.] my_rnd                                                                           ▒

     __clone                                                                                                                  ▒

     start_thread                                                                                                             ▒

     handle_one_connection                                                                                                    ▒

   - do_handle_one_connection                                                                                                 ▒

      - 9.42% do_command                                                                                                      ▒

           dispatch_command                                                                                                   ▒

           mysql_stmt_execute_common                                                                                          ▒

           Prepared_statement::execute_loop                                                                                   ▒

           Prepared_statement::execute                                                                                        ▒

           mysql_execute_command                                                                                              ▒

           execute_sqlcom_select                                                                                              ▒

           handle_select                                                                                                      ▒

           mysql_select                                                                                                       ▒

           JOIN::exec                                                                                                         ▒

           JOIN::exec_inner                                                                                                   ▒

           select_send::send_data                                                                                             ▒

           Protocol::send_result_set_row                                                                                      ▒

           Item::send                                                                                                         ▒

           Type_handler_string_result::Item_send                                                                              ▒

           Type_handler::Item_send_str                                                                                        ▒

         - Item_func_encode::val_str                                                                                          ▒

            - 9.26% Item_func_encode::seed                                                                                    ▒

               - 9.16% SQL_CRYPT::init                                                                                        ▒

                    my_rnd            

  0.04 │      rldicr r9,r6,1,62

       │      rand_st->seed2=(seed1+rand_st->seed2+33) % rand_st->max_value;

       │      addi   r8,r10,33

       │      seed1= (rand_st->seed1*3+rand_st->seed2) % rand_st->max_value;

  5.77 │      add    r9,r9,r6

  0.19 │      add    r10,r9,r10

  0.66 │      divdu  r9,r10,r7

  4.79 │      mulld  r9,r9,r7

  0.07 │      subf   r9,r9,r10

       │      rand_st->seed2=(seed1+rand_st->seed2+33) % rand_st->max_value;

  1.23 │      add    r8,r8,r9

       │      return (((double) seed1)/rand_st->max_value_dbl);

 19.94 │      mtvsrd vs12,r9

       │      rand_st->seed2=(seed1+rand_st->seed2+33) % rand_st->max_value;

  0.08 │      divdu  r10,r8,r7

       │      rand_st->seed1= seed1;

  3.22 │      std    r9,0(r3)

       │      return (((double) seed1)/rand_st->max_value_dbl);

 50.64 │      fcfidu f1,f12

       │    }

  3.38 │      fdiv   f1,f1,f0

       │      rand_st->seed2=(seed1+rand_st->seed2+33) % rand_st->max_value;

  0.19 │      mulld  r9,r10,r7

  2.58 │      subf   r9,r9,r8

  0.32 │      std    r9,8(r3)

       │    }