[20240313]使用tpt ashtop.sql脚本的困惑.txt

--//使用tpt ashtop.sql脚本遇到的问题,做一些分析以及说明:

1.环境：
SYS@127.0.0.1:9014/ywdb> @ver1
PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

2.问题:
SYS@127.0.0.1:9014/ywdb> @ ashtop sql_id sql_id='2cqbg080kv9uh' &day
    Total                                                                         Distinct Distinct
  Seconds     AAS %This   SQL_ID        FIRST_SEEN          LAST_SEEN           Execs Seen  Tstamps
--------- ------- ------- ------------- ------------------- ------------------- ---------- --------
        5      .0  100% | 2cqbg080kv9uh 2024-03-12 14:24:04 2024-03-13 10:54:39          1        5

--//Distinct Execs Seen =1,Distinct Tstamps=5,按照我以前的理解,Distinct Execs Seen相当于执行次数,Distinct Tstamps相当于
--//总的执行时间(注:两条相同sql语句同时执行,sample_time总会有一点点不同,相同的概率应该很低),除非很密集的执行也许可能出现
--//sample_time相同的情况.
--//我看过这条sql语句应该很快完成,根本不可能1次执行需要5秒.

--//感觉那里不对。

3.分析:
--//查看ashtop.sql脚本：
...
      , COUNT(DISTINCT sql_exec_start||':'||sql_exec_id) dist_sqlexec_seen
      , COUNT(DISTINCT sample_time) dist_timestamps
...

SELECT sql_id, sql_exec_start || ':' || sql_exec_id, sample_time
  FROM gV$ACTIVE_SESSION_HISTORY
 WHERE     sql_id = '2cqbg080kv9uh'
       AND sample_time BETWEEN SYSDATE - 1 AND SYSDATE;

SQL_ID        SQL_EXEC_START||':'||SQL_EXEC_ID SAMPLE_TIME
------------- -------------------------------- -----------------------
2cqbg080kv9uh :                                2024-03-12 21:38:48.048
2cqbg080kv9uh :                                2024-03-13 10:54:39.810
2cqbg080kv9uh :                                2024-03-13 08:15:53.122
2cqbg080kv9uh :                                2024-03-12 18:41:53.370
2cqbg080kv9uh :                                2024-03-12 14:24:04.705
       
--//噢!! 原来gV$ACTIVE_SESSION_HISTORY视图有一些情况并没有抓取到SQL_EXEC_START,SQL_EXEC_ID的值，这样看到dist_sqlexec_seen=1.
--//不清楚怎么时候会出现这样的情况。

4.总结:
--//Distinct Execs Seen,Distinct Tstamps 只能作为参考.
--//感觉tpt ashtop.sql脚本应该修改为:
COL dist_sqlexec_seen1  HEAD "Distinct|Execs Seen1" FOR 999999
...
, COUNT(DISTINCT decode(sql_exec_start||':'||sql_exec_id,':',to_char(sample_time,'yyyymmdd hh24:mi:ss.ff3'),sql_exec_start||':'||sql_exec_id)) dist_sqlexec_seen1
--//或者再增加一个字段也许更加合理一些.

SYS@127.0.0.1:9014/ywdb> @ ashtop sql_id sql_id='g7ytdh9mxt1s0' &day
    Total                                                                         Distinct Distinct    Distinct
  Seconds     AAS %This   SQL_ID        FIRST_SEEN          LAST_SEEN           Execs Seen  Tstamps Execs Seen1
--------- ------- ------- ------------- ------------------- ------------------- ---------- -------- -----------
      991      .0  100% | g7ytdh9mxt1s0 2024-03-17 11:52:15 2024-03-18 11:51:11        636      987         991

SYS@127.0.0.1:9014/ywdb> @ sql_id g7ytdh9mxt1s0
--SQL_ID = g7ytdh9mxt1s0
select count ( :"SYS_B_0" ) from BSOFT_TEST_CONNECT ;

--//这条语句执行频率非常高, 执行很快,dist_timestamps=987,如果前面dist_sqlexec_seen表示执行次数,明显不妥.
--//dist_sqlexec_seen1=991,说明有4次(991-987)的sample_time存在重复的.
--//当然不能简单的理解每次执行是dist_timestamps/dist_sqlexec_seen1,对于每次执行超过1秒的有一定的参考价值，可以推断每次执
--//行需要的时间。

SYS@127.0.0.1:9014/ywdb> @ ashtop event  sql_id='g7ytdh9mxt1s0'  &day
    Total                                                                                                      Distinct Distinct    Distinct
  Seconds     AAS %This   EVENT                                      FIRST_SEEN          LAST_SEEN           Execs Seen  Tstamps Execs Seen1
--------- ------- ------- ------------------------------------------ ------------------- ------------------- ---------- -------- -----------
     1266      .0   98% |                                            2024-03-18 08:53:33 2024-03-19 08:52:45        852     1261        1266
       16      .0    1% | log file sync                              2024-03-18 10:37:38 2024-03-18 21:53:48          1       16          16
        9      .0    1% | reliable message                           2024-03-18 09:43:51 2024-03-18 17:58:55          1        9           9
        3      .0    0% | SQL*Net message from dblink                2024-03-18 15:23:43 2024-03-18 16:41:05          1        3           3
        2      .0    0% | latch free                                 2024-03-18 11:22:46 2024-03-18 16:58:07          2        2           2
        1      .0    0% | cursor: pin S                              2024-03-18 09:07:13 2024-03-18 09:07:13          1        1           1
6 rows selected.