使用那个shared pool latch.txt
--//我的测试环境很小,仅仅1个shared pool latch.如果存在多个,一条sql语句应该会使用那个shared pool latch.
--//按照前面的学习,猜测应该于hash_value , bucket_size , _kghdsidx_count 相关,测试看看。
--//注：一般缺省bucket_size ＝2^(9+8) =131072
1.环境:
SCOTTbook> 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
SCOTTbook> select * from dept where deptno=20;
DEPTNO DNAME LOC 20 RESEARCH DALLAS
SCOTTbook> hash
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
95129850 80baj2c2ur47u 0 5ab90fa
SYSbook> hide _kgl_bucket_count
NAME DESCRIPTION DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE ISSES ISSYS_MOD
_kgl_bucket_count Library cache hash table bucket count (2^_kgl_bucket_count * 256) TRUE 9 9 FALSE FALSE
SYSbook> alter system set "_kghdsidx_count"=7 scope=spfile;
System altered.
--//重启数据库略
SELECT addr
,latch#
,child#
,level#
,name
,gets
,sleeps
,immediate_gets
,immediate_misses
,spin_gets
FROM V$LATCH_CHILDRENWHERE name LIKE 'shared pool'
ORDER BY addr;
ADDR LATCH# CHILD# LEVEL# NAME GETS SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES SPIN_GETS
000000006010D9A0 336 1 7 shared pool 10126 0 0 0 29
000000006010DA40 336 2 7 shared pool 6220 0 0 0 5
000000006010DAE0 336 3 7 shared pool 8610 0 0 0 7
000000006010DB80 336 4 7 shared pool 7817 0 0 0 21
000000006010DC20 336 5 7 shared pool 7446 0 0 0 18
000000006010DCC0 336 6 7 shared pool 7302 1 0 0 7
000000006010DD60 336 7 7 shared pool 6347 0 0 0 3
7 rows selected.
--//记下7个addr地址. 000000006010D9A0 000000006010DA40 000000006010DAE0 000000006010DB80 000000006010DC20 000000006010DCC0 000000006010DD60.
2.测试:
--//编辑gdb脚本:
$ cat shared_pool.gdb
set pagination off
break kslgetl if $rdi==0X6010D9A0
commands
silent
printf "child#=1 kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
cend
break kslgetl if $rdi==0X6010DA40
commands
silent
printf "child#=2 kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
cend
break kslgetl if $rdi==0X6010DAE0
commands
silent
printf "child#=3 kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
cend
break kslgetl if $rdi==0X6010DB80
commands
silent
printf "child#=4 kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
cend
break kslgetl if $rdi==0X6010DC20
commands
silent
printf "child#=5 kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
cend
break kslgetl if $rdi==0X6010DCC0
commands
silent
printf "child#=6 kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
cend
break kslgetl if $rdi==0X6010DD60
commands
silent
printf "child#=7 kslgetl %x, %d, %d, %d\n", $rdi, $rsi, $rdx, $rcx
cend
--//先执行Select * from dept where deptno=20;,desc dept多次,避免一些递归.
--// hash_value % bucket_size % _kghdsidx_count
--// 95129850 % 7 = 4
--// 95129850 % 131072 % 7 = 2
--//验证看看使用那个shared pool latch.
--//session 1:
SCOTTbook(1,7)> spid
SID SERIAL# PROCESS SERVER SPID PID P_SERIAL# C50 1 7 4691 DEDICATED 4692 24 4 alter system kill session '1,7' immediate;
SCOTTbook> select * from dept where deptno=20;
DEPTNO DNAME LOC 20 RESEARCH DALLAS
--//session 2:
$ gdb -p 4692 -x shared_pool.gdb
...
Breakpoint 1 at 0x93f97a8
(gdb) c
...
child#=3 kslgetl 6010dae0, 1, 0, 4039
child#=3 kslgetl 6010dae0, 1, 0, 3980
child#=3 kslgetl 6010dae0, 1, 0, 4039
child#=3 kslgetl 6010dae0, 1, 2132183136, 3991
--//6010dae0 对应的就是CHILD#＝3.
--//估计 hash_value % bucket_size % _kghdsidx_count + 1 . 或者 _kghdsidx_count-hash_value % _kghdsidx_count(不对!!)
--//可以大致推测使用的计算公式是 hash_value % bucket_size % _kghdsidx_count + 1
--//多找几条sql语句验证看看。
3.继续验证看看.
--//注意验证前最好执行select sysdate from dual;多次排除游戏的链接中遇到的影响。
--//因为11g下sqlplus执行后不会马上释放光标，导致看到的是前面的语句，这样可能不对。
--//session 3，主要目的确定hash_value:
SCOTTbook> select * from dept where deptno=10;
DEPTNO DNAME LOC 10 ACCOUNTING NEW YORK
SCOTTbook> hash
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
911274289 4xamnunv51w9j 1 3650f131
--// 911274289 % 131072 % 7 +1 = 6
SCOTTbook> select * from dept where deptno=30;
DEPTNO DNAME LOC 30 SALES CHICAGO
SCOTTbook> hash
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
69952862 816w0g822qtay 0 42b655e
--// 69952862 % 131072 % 7+1 = 4
SCOTTbook> select * from dept where deptno=40;
DEPTNO DNAME LOC 40 OPERATIONS BOSTON
SCOTTbook> hash
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
3912471479 14ymr4znm74xr 0 e93393b7
--// 3912471479 % 131072 % 7 +1 = 4
SCOTTbook> select * from dept where deptno=50;
no rows selected
SCOTTbook> hash
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
1927948053 bswp9zttfn9sp 0 72ea2715
--//1927948053 % 131072 % 7 +1 = 3
--//session 1:
--//再次提醒执行www.cungun.comselect sysdate from dual;多次。
select sysdate from dual;
select sysdate from dual;
select sysdate from dual;
select sysdate from dual;
select sysdate from dual;
select * from dept where deptno=10;
select sysdate from dual;
select sysdate from dual;
select * from dept where deptno=30;
select sysdate from dual;
select sysdate from dual;
select * from dept where deptno=40;
select sysdate from dual;
select sysdate from dual;
select * from dept where deptno=50;
--//session 2:
$ gdb -p 4692 -x shared_pool.gdb
...
child#=6 kslgetl 6010dcc0, 1, 0, 3980 => select * from dept where deptno=10; => child#=6
...
child#=4 kslgetl 6010db80, 1, 0, 3980 => select * from dept where deptno=30; => child#=4
...
child#=4 kslgetl 6010db80, 1, 0, 3980 => select * from dept where deptno=40; => child#=4
...
child#=3 kslgetl 6010dae0, 1, 0, 4039 => select * from dept where deptno=50; => child#=3
--//OK.都能对上。
总结:
--//说明一条sql语句会使用 其sql语句的 hash_value % bucket_size % _kghdsidx_count +1 的 shared pool latch.