[20190423]那个更快的疑问3.txt

--//前一阵子,做了11g在单表单条记录唯一索引扫描的测试,摘要如下:
--//参考链接:
http://blog.itpub.net/267265/viewspace-2636321/
http://blog.itpub.net/267265/viewspace-2636342/

--//在链接中我解析唯一索引查询的情况，为什么10g快于11g，链接：http://blog.itpub.net/267265/viewspace-2639920/
--//差异在于10g很少做times的系统调用上.10g下仅仅116次.而11g高达200179.(getrusage与times调用次数比大约是7:2)
--//我当时的感觉10g漏写times系统函数调用，导致这样的情况，11g把它补上了。
--//实际上有网友提出疑问.我的测试下的结论有问题.当时测试的情况如下:
--//11g的测试:
$ strace -f -c sqlplus -s -l scott/book @m1.txt 1e5 id=1_unique_index 0 >/dev/null
...
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 72.78    0.043919           0    700708           getrusage
 19.80    0.011947           0    200179           times
  6.67    0.004024         671         6         3 wait4
  0.24    0.000147          29         5           clone
  0.18    0.000106           0       375         2 read
  0.16    0.000096           0       264       106 open
...
------ ----------- ----------- --------- --------- ----------------
100.00    0.060341                902967       206 total

--//1e5次执行times调用消耗0.011947秒,放大10倍(我每个session执行次数是1e6)也就是0.119470秒,什么可能产生这么大的差异.
--//仔细查看,我觉得strace跟踪记录的syscallsyscall.linux标准C函数.看不出oracle内部函数调用次数.
--//我当时的解析是这增加的times调用一定是11g版本唯一索引扫描中增加几个oracle内部函数调用,导致11g的唯一索引
--//扫描更慢,如何验证我当时确实不知道? 最近shared latch测试,建立一些gdb脚本,有了这些脚本可以latch获得释放的情况.

1.环境:
SCOTT@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

2.建立测试脚本:

create table t as select rownum id from dual ;
create unique index pk_t on t(id);
alter table t modify id  not null ;
create table job_times (sid number, time_ela number,method varchar2(20));
--//分析表略.

$ cat z1.txt
set verify off
host sleep $(echo &&3/50 | bc -l )
variable vmethod varchar2(20);
exec :vmethod := '&&2';
insert into job_times values ( sys_context ('userenv', 'sid') ,dbms_utility.get_time ,:vmethod) ;
commit ;
declare
v_id number;
v_d date;
begin
    for i in 1 .. &&1 loop
        select /*+  &&3 */ count (*) into v_id from t where id=1 ;
    end loop;
end ;
/
update job_times set time_ela = dbms_utility.get_time - time_ela where sid=sys_context ('userenv', 'sid') and method=:vmethod;
commit;
quit

3.分别测试:
$ sqlplus -s -l scott/book @z1.txt 1e6 id=unindex 0 >/dev/null

SCOTT@book> Select method,count(*),round(avg(TIME_ELA),0),sum(TIME_ELA) from job_times group by method order by 3 ;
METHOD                 COUNT(*) ROUND(AVG(TIME_ELA),0) SUM(TIME_ELA)
-------------------- ---------- ---------------------- -------------
id=unindex                    1                   2723          2723

--//在10g下重复测试:
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

SCOTT@test> select method,count(*),round(avg(TIME_ELA),0),sum(TIME_ELA) from job_times group by method order by 3 ;
METHOD                 COUNT(*) ROUND(AVG(TIME_ELA),0) SUM(TIME_ELA)
-------------------- ---------- ---------------------- -------------
id=unindex                    1                   1591          1591
--//即使单用户执行10g下比11g快许多.

3.通过gdb脚本分析:
--//11g:
SCOTT@book> @ spid
       SID    SERIAL# PROCESS                  SERVER    SPID       PID  P_SERIAL# C50
---------- ---------- ------------------------ --------- ------ ------- ---------- --------------------------------------------------
        88         89 65066                    DEDICATED 65067       30         65 alter system kill session '88,89' immediate;

--//执行多次3次以上避免递归.
select count(*) from t where id=1;
--//打开window 2:
$ gdb -p 65067 -x latch11g.gdb
(gdb) c
Continuing.
ksl_get_shared_latch laddr:85f7fe28, willing:1, where:-2050764096, why:95, mode:8
ksl_get_shared_latch laddr:85f7fe28, willing:1, where:-2050764096, why:96, mode:16
ksl_get_shared_latch laddr:85f7fe28, willing:1, where:-2050764096, why:95, mode:8
kslgetl 844ed538, 0, 49, 2062
kslgetl 8353a258, 1, 16777771, 2053
ksl_get_shared_latch laddr:85f7fe28, willing:1, where:-2050764096, why:96, mode:16
ksl_get_shared_latch laddr:85f7fe28, willing:1, where:-2050764096, why:95, mode:8
ksl_get_shared_latch laddr:85f7fe28, willing:1, where:-2050764096, why:96, mode:16

--//看到ksl_get_shared_latch 6次,kslgetl 2次,看看是什么latch.
> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('85f7fe28'),'16','0')
ADDR             NAME             LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- ---------------- ------ ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
0000000085F7FE28 session idle bit      1         14       1095          0          0              0                0             0                   0          0          0

--//session idle bit 第一次看见,我看了我的测试机器,一共24次children latch.估计跟CPU数量有关.我在另外的会话重复测试
--//ksl_get_shared_latch的地址不一样,而kslgetl 也是2次都是一样.

> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('844ed538'),'16','0')
ADDR             NAME                LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- ------------------- ------ ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
00000000844ED538 simulator lru latch      6        185        560          1          0       72795239          3207148             0                   0          1          0

> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('8353a258'),'16','0')
ADDR             NAME                 LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- -------------------- ------ ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
000000008353A258 simulator hash latch      7        186   72792634          0          0              0                0             0                   0          0          0

--//奇怪这两个latch我从来没有过,而且奇怪的是根本看不到cbc latch.
--//在10g下重复测试看看(注10g shared latch 的函数是kslgetsl )

Breakpoint 1 at 0x7a0644
Breakpoint 2 at 0x7a0a44
Breakpoint 3 at 0x3bccd52
Breakpoint 4 at 0x3be9a04
Breakpoint 5 at 0x3181cd6400
Breakpoint 6 at 0x78ef44
Function "ksl_get_shared_latch" not defined.
Make breakpoint pending on future shared library load? (y or [n]) [answered N; input not from terminal]
Breakpoint 7 at 0x78f4bc
Breakpoint 8 at 0x79054c
--//奇怪10g没有ksl_get_shared_latchoracle内部函数.注解这部分内容.

(gdb) c
Continuing.
kslgetsl laddr:7cfb24f8, willing:1, where:2096584384, why:80, mode:8
kslgetsl laddr:7cfb24f8, willing:1, where:2096584384, why:81, mode:16
kslgetsl laddr:7cfb24f8, willing:1, where:2096584384, why:80, mode:8
kslgetl 7a10aaa0, 1, 0, 2741
kslgetsl laddr:7cfb24f8, willing:1, where:2096584384, why:81, mode:16
kslgetsl laddr:7cfb24f8, willing:1, where:2096584384, why:80, mode:8
kslgetsl laddr:7cfb24f8, willing:1, where:2096584384, why:81, mode:16
--//看到kslgetsl 6次,kslgetl 1次,看看是什么latch.
SYS@test> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('7cfb24f8'),'16','0');
ADDR             NAME                 LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- -------------------- ------ ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
000000007CFB24F8 session idle bit          1          7       7112          0          0              0                0             0                   0          0          0

SYS@test> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('7a10aaa0'),'16','0');
ADDR             NAME                   LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- ---------------------- ------ ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
000000007A10AAA0 shared pool simulator       8        241     146325          1          0              0                0             0                   0          1          0

--//你可以再次执行sql语句看看gets的变化:
SYS@test> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('7cfb24f8'),'16','0');
ADDR             NAME             LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- ---------------- ------ ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
000000007CFB24F8 session idle bit      1          7       7118          0          0              0                0             0                   0          0          0

SYS@test> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('7a10aaa0'),'16','0');
ADDR             NAME                  LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- --------------------- ------ ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
000000007A10AAA0 shared pool simulator      8        241     146326          1          0              0                0             0                   0          1          0

--//说明跟踪到的get变化没有问题.我在11g看了latch的变化,只不过simulator lru latch 变成了IMMEDIATE_GETS数量增加:
> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('8353a258'),'16','0')
ADDR             NAME                                         LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- ---------------------------------------- ---------- ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
000000008353A258 simulator hash latch                              7        186   72792639          0          0              0                0             0                   0          0          0

> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('844ed538'),'16','0')
ADDR             NAME                                         LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- ---------------------------------------- ---------- ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
00000000844ED538 simulator lru latch                               6        185        563          1          0       72795248          3207148             0                   0          1          0

--//执行sql语句再查看.
> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('8353a258'),'16','0')
ADDR             NAME                                         LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- ---------------------------------------- ---------- ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
000000008353A258 simulator hash latch                              7        186   72792640          0          0              0                0             0                   0          0          0

> select addr,name,level#,latch#,gets,misses,sleeps,immediate_gets,immediate_misses,waiters_woken,waits_holding_latch,spin_gets,wait_time from v$latch_children where addr=lpad(upper('844ed538'),'16','0')
ADDR             NAME                                         LEVEL#     LATCH#       GETS     MISSES     SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH  SPIN_GETS  WAIT_TIME
---------------- ---------------------------------------- ---------- ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
00000000844ED538 simulator lru latch                               6        185        563          1          0       72795249          3207148             0                   0          1          0

--//我估计跟一些参数有关:
kslgetl 844ed538, 0, 49, 2062
kslgetl 8353a258, 1, 16777771, 2053
--//我猜测0表示no willing等待. 1表示willing等待.
--//我最后猜测也许正是11g下代码改动使用ksl_get_shared_latch,多了1次kslgetl调用,使用导致11g下每次执行多了2次times syscall,
--//可以讲11g下唯一索引扫描是一个退步.
--//至于为什么没有阻塞看不到cbc latch获取和释放,我给再探究看看...

4.我加入1个字段看看:
drop table t purge ;
create table t as select rownum id,'test' name  from dual ;
create unique index pk_t on t(id);
alter table t modify id  not null ;

$ cat z1.txt
set verify off
host sleep $(echo &&3/50 | bc -l )
variable vmethod varchar2(20);
exec :vmethod := '&&2';
insert into job_times values ( sys_context ('userenv', 'sid') ,dbms_utility.get_time ,:vmethod) ;
commit ;
declare
v_id number;
v_d date;
v_name varchar2(4) ;
begin
    for i in 1 .. &&1 loop
        select /*+  &&3 */ name  into v_name from t where id=1 ;
    end loop;
end ;
/
update job_times set time_ela = dbms_utility.get_time - time_ela where sid=sys_context ('userenv', 'sid') and method=:vmethod;
commit;
quit

--//重复测试:
--//11g:
SCOTT@book> Select method,count(*),round(avg(TIME_ELA),0),sum(TIME_ELA) from job_times group by method order by 3 ;
METHOD                 COUNT(*) ROUND(AVG(TIME_ELA),0) SUM(TIME_ELA)
-------------------- ---------- ---------------------- -------------
id=unindex_name               1                   2135          2135
id=unindex                    1                   2723          2723

--//10g:
SCOTT@test> select method,count(*),round(avg(TIME_ELA),0),sum(TIME_ELA) from job_times group by method order by 3 ;
METHOD                 COUNT(*) ROUND(AVG(TIME_ELA),0) SUM(TIME_ELA)
-------------------- ---------- ---------------------- -------------
id=unindex_name               1                   1359          1359
id=unindex                    1                   1591          1591

--//真心搞不懂,回表反而更快一些.oracle许多东西真心搞不懂....
--//感觉如果访问数据块缓存数据块,没有阻塞无需要获取cbc latch吗?

5.附上gdb脚本:
--//11g版本:
$ cat latch11g.gdb
break kslgetl
  commands
    silent
    printf "kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break kslges
  commands
    silent
    printf "kslges %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break skgpwwait
  commands
    silent
    printf "skgpwwait %d, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break sskgpwwait
  commands
    silent
    printf "sskgpwwait %d, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break semop
  commands
    silent
    printf "semop %d, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

#break *0x93f9ddc
#  commands
#    silent
#    printf " spin count loop: %d %d %x\n", $rax,$rcx,$rip
#    c
#  end

##
break kslgetsl_w
  commands
    silent
    printf "kslgetsl_w laddr:%x, willing:%d, where:%d, why:%d, mode:%d\n", $rdi, $rsi, $rdx, $rcx, $r8
    c
  end

break ksl_get_shared_latch
  commands
    silent
    printf "ksl_get_shared_latch laddr:%x, willing:%d, where:%d, why:%d, mode:%d\n", $rdi, $rsi, $rdx, $rcx, $r8
    c
  end

break kslgess
  commands
    silent
    printf "kslgess %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break kslskgs
  commands
    silent
    printf "kslskgs %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break kslfre
  commands
    silent
    printf "kslfre %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

#break *0xa875be
#  commands
#    silent
#    printf " spin count loop: %d %x\n", $r13,$rip
#    c
#  end

--//10g版本:
$ cat latch10g.gdb
break kslgetl
  commands
    silent
    printf "kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break kslges
  commands
    silent
    printf "kslges %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break skgpwwait
  commands
    silent
    printf "skgpwwait %d, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break sskgpwwait
  commands
    silent
    printf "sskgpwwait %d, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break semop
  commands
    silent
    printf "semop %d, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

#break *0x93f9ddc
#  commands
#    silent
#    printf " spin count loop: %d %d %x\n", $rax,$rcx,$rip
#    c
#  end

##
break kslgetsl
  commands
    silent
    printf "kslgetsl laddr:%x, willing:%d, where:%d, why:%d, mode:%d\n", $rdi, $rsi, $rdx, $rcx, $r8
    c
  end

#break ksl_get_shared_latch
#  commands
#    silent
#    printf "ksl_get_shared_latch laddr:%x, willing:%d, where:%d, why:%d, mode:%d\n", $rdi, $rsi, $rdx, $rcx, $r8
#    c
#  end

break kslgess
  commands
    silent
    printf "kslgess %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

break kslskgs
  commands
    silent
    printf "kslskgs %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
    c
  end

#break *0xa875be
#  commands
#    silent
#    printf " spin count loop: %d %x\n", $r13,$rip
#    c
#  end

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