Use the shared pool latch.txt
–// Our test environment is small, only 1 shared pool latch. If there is a shared pool latch, a single SQL statement should use the shared pool latch. –// Bucket_size = 2^(9+8) =131072
1. Environment: SCOTT@book >@ver1 PORT_STRING VERSION BANNER
X86_64 /Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition 11.2.0.4.0-64bit Production
SCOTT@book> select * from dept where deptno=20;
DEPTNO DNAME LOC 20 RESEARCH DALLAS
SCOTT@book> @ hash
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
95129850 80baj2c2ur47u 0 5ab90fa
SYS@book> @ 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
SYS@book> alter system set “_kghdsidx_count”=7 scope=spfile;
System altered.
–// Restart the database
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. –// Recall 7 addr addresses. 000000006010DA40 000000006010DAE0 000000006010DB80 000000006010DC20 000000006010DCC0 000000006010DD60.
$cat shared_pool. GDB set pagination off. $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
Select * from dept where deptno=20; –// hash_value % bucket_size % _kghdsidx_count –// 951299850%7 = 4 –// 951299850%131072%7 = 4 –// 951299850%131072%7 = 4 2
–// Session 1: SCOTT@book(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;
SCOTT@book> 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, Hash_value % bucket_size % _kghdsidx_count + 1. Or _kghdsidx_count-hash_value % _kghdsidx_count(no!!). –// hash_value % bucket_size % _kghdsidx_count + 1 —
Select sysdate from dual; select sysdate from dual; * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
–// select * from hash_value where hash_value = ‘#’;
SCOTT@book> select * from dept where deptno=10;
DEPTNO DNAME LOC 10 ACCOUNTING NEW YORK
SCOTT@book> @ hash
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
911274289 4xamnunv51w9j 1 3650f131
–// 911274289 % 131072 % 7 +1 = 6
SCOTT@book> select * from dept where deptno=30;
DEPTNO DNAME LOC 30 SALES CHICAGO
SCOTT@book>
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
69952862 816w0g822qtay 0 42b655e
–// 69952862 % 131072 % 7+1 = 4
SCOTT@book> select * from dept where deptno=40;
DEPTNO DNAME LOC 40 OPERATIONS BOSTON
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
3912471479 14ymr4znm74xr 0 e93393b7
–// 3912471479 % 131072 % 7 +1 = 4
SCOTT select * from dept where deptno=50;
no rows selected
HASH_VALUE SQL_ID CHILD_NUMBER HASH_HEX
1927948053 bswp9zttfn9sp 0 72ea2715
–//1927948053 % 131072 % 7 +1 = 3
–// Session 1: –// select sysdate from dual; Many a time. 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.
SQL statement that uses hash_value % bucket_size % _kghdsidx_count +1 shared pool latch