--//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.
http://andreynikolaev.wordpress.com/2010/04/12/latch-internals-information-sources/
--//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
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 Datab