[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.