[20190401]关于semtimedop函数调用.txt

--//上个星期测试,链接http://blog.itpub.net/267265/viewspace-2639675/
--//关于sql语句中mutexes的问题,实际上仅仅涉及cursor: pin S.
--//我的测试说明这个mutexes在父光标的堆0中.

--//我当时相当然认为:
16:04:56.410785 semtimedop(309166080, 0x7fff83068fd0, 1, {0, 10000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.010684>
--//{0, 10000000} 是 timespec. 前面单位是秒,后面单位是纳秒(毫微秒) 1秒=10^9纳秒, 10000000/10^9 = .01.
--//这样每次调用semtimedop需要0.010xXX秒.
--//我的理解相当于不断spin,检查这个资源是否可用.2秒后调用getrusage.
--//我一直以为0.010684秒中的0.000684秒是spin的时间,犯了一个严重错误,主要不熟悉os函数调用.

--//实际上semtimedop函数调用.里面的{0, 10000000}定义的是最大延迟，即睡眠。这里是0.01是秒(注后面的单位是纳秒).
--//做一个测试就很容易理解:

1.环境:
SCOTT@test> @ &r/ver1

PORT_STRING                    VERSION        BANNER
------------------------------ -------------- ----------------------------------------------------------------
x86_64/Linux 2.4.xx            10.2.0.4.0     Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
--//注10g下好观察一些.

2.测试:
$ ps -ef | grep ora_lgwr_tes[t]
oracle   19051     1  0 Mar20 ?        00:00:03 ora_lgwr_test

# strace -frT -e semtimedop -p 19051
Process 19051 attached - interrupt to quit
     0.000000 semtimedop(12320769, 0x7fff1bef85b0, 1, {2, 410000000}) = -1 EAGAIN (Resource temporarily unavailable) <2.411183>
     2.411526 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001731>
     3.002135 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001646>
     3.001937 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001758>
     3.002166 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001638>

...
--//在没有任何事务的情况下,延迟3秒.打开一个会话执行如下:
SCOTT@test> select * from t for update;
        ID
----------
         1

SCOTT@test> commit;
Commit complete.

# strace -frT -e semtimedop -p 19051
...
     3.001200 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001597>
     3.001884 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000763>
     3.001165 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001639>
     3.001925 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001772>
     3.002179 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001661>
     3.001949 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001761>
     3.002166 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = 0 <1.433330>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~    
     1.433937 semtimedop(12320769, 0x7fff1bef85b0, 1, {1, 570000000}) = -1 EAGAIN (Resource temporarily unavailable) <1.571702>
     1.572208 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001549>
     3.001953 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000633>
     3.000920 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000752>
     3.001153 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0} <unfinished ...>

--//注意看下划线那行,如果有事务执行并提交,并没有等待3秒就唤醒了写日志进程.

3.继续测试:
--//再做一个测试看看:
$ cat b1.txt
host sleep 10
select t.*,systimestamp from t for update;
host sleep 10
select systimestamp from dual;
commit ;
select systimestamp from dual;
quit

# strace -fttT -e semtimedop -p 19051
...

$ sqlplus -s -l scott/btbtms @b1.txt

ID SYSTIMESTAMP
---------- ---------------------------------
         1 2019-04-01 11:40:45.895129 +08:00

SYSTIMESTAMP
---------------------------------
2019-04-01 11:40:55.903089 +08:00

Commit complete.

SYSTIMESTAMP
---------------------------------
2019-04-01 11:40:55.905283 +08:00

# strace -fttT -e semtimedop -p 19051
...
11:40:40.857303 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000738>
11:40:43.858463 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000628>
11:40:46.859403 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000740>
11:40:49.860569 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000629>
11:40:52.861505 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000749>
11:40:55.862679 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = 0 <0.041530>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
11:40:55.904831 semtimedop(12320769, 0x7fff1bef85b0, 1, {2, 960000000}) = -1 EAGAIN (Resource temporarily unavailable) <2.961459>
11:40:58.866605 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000734>
11:41:01.867766 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000631>
11:41:04.868703 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000733>
11:41:07.869856 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001637>
11:41:10.871801 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.000741>
11:41:13.872963 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001630>
11:41:16.874922 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001737>
11:41:19.877089 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = -1 EAGAIN (Resource temporarily unavailable) <3.001619>

--//commit的时间在2019-04-01 11:40:55.903089- 2019-04-01 11:40:55.905283 之间.
--//strace看到的时间是       11:40:55.904831 ,正好在前面两个时间之间.
--//注意下划线这行显示11:40:55.862679 semtimedop(12320769, 0x7fff1bef85b0, 1, {3, 0}) = 0 <0.041530> 的时间不是提交时间.
--//这行前面的时间是开始执行semtimedop调用的时间,在0.041530秒后有事务提交,唤醒.
--//0.862679+0.041530 = .904209,也就是11:40:55.904209 这行调用执行结束.
--//在11:40:55.904831开始执行新的semtimedop调用.
--//也就是commit应该在11:40:55.904209 - 11:40:55.904831 之间.

4.补充11g的lgwr进程的跟踪:
$ ps -ef | grep ora_lgwr_boo[k]
oracle   56345     1  0 08:38 ?        00:00:02 ora_lgwr_book

$ strace -e semtimedop -fTr -p 56345
Process 56345 attached - interrupt to quit
     0.000000 semtimedop(309821440, 0x7fff39b50600, 1, {2, 980000000}) = 0 <0.629618>
     0.629992 semtimedop(309821440, 0x7fff39b50600, 1, {2, 350000000}) = 0 <1.000813>
     1.001257 semtimedop(309821440, 0x7fff39b50600, 1, {1, 350000000}) = 0 <1.000513>
     1.000871 semtimedop(309821440, 0x7fff39b50600, 1, {0, 350000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.350287>
     0.350597 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.649906>
     0.650342 semtimedop(309821440, 0x7fff39b50600, 1, {2, 350000000}) = 0 <1.000628>
     1.000987 semtimedop(309821440, 0x7fff39b50600, 1, {1, 350000000}) = 0 <1.000696>
     1.001135 semtimedop(309821440, 0x7fff39b50600, 1, {0, 350000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.350213>
     0.350491 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.649969>
     0.650330 semtimedop(309821440, 0x7fff39b50600, 1, {2, 350000000}) = 0 <1.000795>
     1.001246 semtimedop(309821440, 0x7fff39b50600, 1, {1, 350000000}) = 0 <1.000516>
     1.000890 semtimedop(309821440, 0x7fff39b50600, 1, {0, 350000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.350268>
     0.350541 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.649974>
     0.650411 semtimedop(309821440, 0x7fff39b50600, 1, {2, 350000000}) = 0 <1.000721>
     1.001088 semtimedop(309821440, 0x7fff39b50600, 1, {1, 350000000}) = 0 <1.000562>
     1.001006 semtimedop(309821440, 0x7fff39b50600, 1, {0, 350000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.350197>
     0.350476 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.649954>
     0.650309 semtimedop(309821440, 0x7fff39b50600, 1, {2, 350000000}) = 0 <1.000833>
     1.001281 semtimedop(309821440, 0x7fff39b50600, 1, {1, 350000000}) = 0 <1.000374>
     1.000735 semtimedop(309821440, 0x7fff39b50600, 1, {0, 350000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.350394>
     0.350669 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.649987>
     0.650427 semtimedop(309821440, 0x7fff39b50600, 1, {2, 350000000}) = 0 <1.000708>
     1.001073 semtimedop(309821440, 0x7fff39b50600, 1, {1, 350000000}) = 0 <1.000603>
     1.001057 semtimedop(309821440, 0x7fff39b50600, 1, {0, 350000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.350159>
     0.350610 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.649828>
     0.650185 semtimedop(309821440, 0x7fff39b50600, 1, {2, 350000000}) = 0 <1.000709>
     1.001164 semtimedop(309821440, 0x7fff39b50600, 1, {1, 350000000}) = 0 <1.000611>
     1.000971 semtimedop(309821440, 0x7fff39b50600, 1, {0, 340000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.340228>
     0.340497 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.659984>
     0.660416 semtimedop(309821440, 0x7fff39b50600, 1, {2, 340000000}) = 0 <1.000653>
     1.001011 semtimedop(309821440, 0x7fff39b50600, 1, {1, 340000000}) = 0 <1.000685>
     1.001131 semtimedop(309821440, 0x7fff39b50600, 1, {0, 340000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.340188>
     0.340463 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.659989>
     0.660341 semtimedop(309821440, 0x7fff39b50600, 1, {2, 340000000}) = 0 <1.000807>
     1.001257 semtimedop(309821440, 0x7fff39b50600, 1, {1, 340000000}) = 0 <1.000387>
     1.000759 semtimedop(309821440, 0x7fff39b50600, 1, {0, 340000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.340378>
     0.340654 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.659976>
     0.660422 semtimedop(309821440, 0x7fff39b50600, 1, {2, 340000000}) = 0 <1.000706>
     1.001074 semtimedop(309821440, 0x7fff39b50600, 1, {1, 340000000}) = 0 <1.000505>
     1.000949 semtimedop(309821440, 0x7fff39b50600, 1, {0, 340000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.340262>
     0.340545 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.660729>
     0.661088 semtimedop(309821440, 0x7fff39b50600, 1, {2, 340000000}) = 0 <1.001027>
     1.001473 semtimedop(309821440, 0x7fff39b50600, 1, {1, 330000000}) = 0 <1.000509>
     1.000870 semtimedop(309821440, 0x7fff39b50600, 1, {0, 330000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.330292>
     0.330581 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.669970>
     0.670416 semtimedop(309821440, 0x7fff39b50600, 1, {2, 330000000}) = 0 <1.000633>
     1.001002 semtimedop(309821440, 0x7fff39b50600, 1, {1, 330000000}) = 0 <1.000676>
     1.001127 semtimedop(309821440, 0x7fff39b50600, 1, {0, 330000000}) = -1 EAGAIN (Resource temporarily unavailable) <0.330172>
     0.330447 semtimedop(309821440, 0x7fff39b50600, 1, {3, 0}) = 0 <0.669963>
     0.670316 semtimedop(309821440, 0x7fff39b50600, 1, {2, 330000000}^C <unfinished ...>
Process 56345 detached

--//还记得链接:http://blog.itpub.net/267265/viewspace-2638170/的测试吗?
--//在没有事务的情况下.每秒scn增加1,日志块增加1,我开始怀疑是否跟我访问这些内存"表"有关.
--//换1个方式测试,取消check.sql后面的host sleep 1,改成sleep 30后,看到的情况每秒scn增加1,日志块增加1.
--//从跟踪上也基本验证我看到的情况.11G会"空转",导致在没有事务产生的情况下,日志也在不断增加.
--//这样11g的日志即使是很空闲的数据库日志增加也会比10g大.

5.最后:
--//理解这些就知道如何测试11g下mutext相关隐含参数,特别是_mutex_spin_count:
SYS@book> @ 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

SYS@book> @ hide mutex
NAME               DESCRIPTION        DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE
------------------ ------------------ ------------- ------------- -------------
_mutex_spin_count  Mutex spin count   TRUE          255           255
_mutex_wait_scheme Mutex wait scheme  TRUE          2             2
_mutex_wait_time   Mutex wait time    TRUE          1             1

--//另外写一篇blog说明.

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