--//我对这个问题的理解就是如果参数willing=0,表示无法获取该latch，直接退出，再寻找类似的latch。
--//我仅仅知道redo copy latch具有这个特性：
> 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 lower(name) like '%'||lower('redo copy')||'%' ;
ADDR NAME LEVEL# LATCH# GETS MISSES SLEEPS IMMEDIATE_GETS IMMEDIATE_MISSES WAITERS_WOKEN WAITS_HOLDING_LATCH SPIN_GETS WAIT_TIME
---------------- ---------- ------ ---------- ---------- ---------- ---------- -------------- ---------------- ------------- ------------------- ---------- ----------
00000012D720ADA8 redo copy 4 208 53 0 0 500627938 304381 0 0 0 0
00000012D720ACD0 redo copy 4 208 53 0 0 497827706 323330 0 0 0 0
..
00000012D72086D8 redo copy 4 208 53 0 0 491448415 365472 0 0 0 0
00000012D7208600 redo copy 4 208 53 0 0 508008338 391955 0 0 0 0
48 rows selected.
--//你可以发现nowait latch 的一个特点,就是IMMEDIATE_GETS会相对很高.注我查询的生产系统的情况.测试环境不会这么高的.
--//参数如下，另外我前面blog写错了，where是最后1个参数。
kslgetl(laddr, wait, why, where) – Get exclusive latch
More precisely, to request the latch Oracle kernel needs:
--//更准确地说，要请求闩锁Oracle内核需要：
laddress -- address of latch in SGA
wait -- flag. If true, this is latch get in willing-to-wait mode..
why -- context why the latch is acquired at this where.
where -- code for location from where the latch is acquired.
1.环境:
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
--//参考链接如下:=>[20190416]exclusive latch测试脚本.txt
$ cat peek.sh
#! /bib/bash
# 参数如下:latch_name Monitoring_duration or laddr
sqlplus -s -l / as sysdba <<EOF
col laddr new_value laddr
SELECT sysdate,addr laddr FROM v\$latch_parent WHERE;
oradebug setmypid
$(seq $2|xargs -I{} echo -e 'oradebug peek 0x&laddr 8\nhost sleep 1' )
EOF
$ cat exclusive_latch.txt
/* 参数如下: @ exclusive_latch.txt latch_name willing why where sleep_num */
--//connect / as sysdba
col laddr new_value laddr
SELECT addr laddr FROM v$latch_parent WHERE;
oradebug setmypid
oradebug call kslgetl 0x&laddr &&2 &&3 &&4
host sleep &&5
oradebug call kslfre 0x&laddr
--//exit
$ cat y1.sh
#! /bin/bash
zdate=$(date '+%Y%m%d%H%M%S')
echo $zdate
source peek.sh 'test excl. parent2 l0' 20 | timestamp.pl >| /tmp/peekx_${zdate}.txt &
seq 20 | xargs -I{} echo -e 'sqlplus -s -l / as sysdba <<< @latch_free\nsleep 1' | bash >| /tmp/latch_freeo_${zdate}.txt &
# 参数如下: @ exclusive_latch.txt latch_name willing why where sleep_num
sqlplus / as sysdba <<< "@ exclusive_latch.txt 'test excl. parent2 l0' 0 1 2 6" > /dev/null &
sleep 2
sqlplus / as sysdba <<< "@ exclusive_latch.txt 'test excl. parent2 l0' 0 3 4 6" > /dev/null &
sleep 4.1
sqlplus / as sysdba <<< "@ exclusive_latch.txt 'test excl. parent2 l0' 0 5 6 6" > /dev/null &
wait