The other day, we found high occurrence of latch events in our principal/core environment (11.2.0.3.0). The origins are all “different businesses channels” that access objects through the use of VPD. The latch events was bit by bit dominating the environment during the last months and turn on an “attention alarm” to us.
Then we found the the note: Bug 12772404 – Significant “row cache objects” latch contention when using VPD – superseded (Doc ID 12772404.8).
The situation is right the same:
“When VPD is used, intense row cache objects latch contention (dc_users) may caused by an internal Exempt Access Policy privilege check. Rediscovery Information:
VPD is in use
Significant “latch: row cache objects” waits occur
The waits are for the latch covering dc_users”
Take a look on the DC_USERS latches:
And about the workaround:
“There is no direct workaround available.
The following guidelines may help to alleviate the problem :
– Dropping the database roles from our user:
The Number of Roles granted to user can increase the row cache
look-ups proportionally. When database is required to check whether
a system privilege is granted to User, it checks if that privilege
is granted to any of the User’s roles. Hence, it’s not helpful
to do something like “set role A, B, C, D, F …” to recreate its
environment for every execution.
– Changing the policy function might be helpful in some cases
eg: To use CONTEXT dependent policies instead of DYNAMIC policies”
Take a look in one of the examples of:
boesing@mydb4> /
P1RAW EVENT USERNAME SQL_ID SQL_CHILD_NUMBER LAST_CALL_ET SID SEQ# WAIT_TIME SECOND
--------- ---------------- ------ ------ ---------- ---------- ------
0700011807B50D08 latch: row cache objects CHANNELAPP 4nwvpx8xt3h3m 22 0 1276 59113 0
0700011807B50D08 latch: row cache objects CHANNELAPP fp3mft3usb74w 0 21719 16636 0
0700011807B50D08 latch: row cache objects CHANNELAPP 58pund2p09hgg 0 6774 11061 0
0700011807B50D08 latch: row cache objects OTHER_CHANNELAPP 54a2wfa60rgu1 1 0 8046 12386 0
0700011807B50D08 latch: row cache objects CHANNELAPP 1gwr69wduk9v4 42 0 9454 53927 0
0700011807B50D08 latch: row cache objects OTHER_CHANNELAPP 9pqrqqfzukrq4 68 0 9732 19311 0
0700011807B50D08 latch: row cache objects CHANNELAPP d1bnq8wb0nhrf 0 1 11425 56830 -1
0700011807B50D08 latch: row cache objects CHANNELAPP 32aqdd8cbmc4b 0 11711 39182 0
0700011807B50D08 latch: row cache objects IB_RUN adgnrpwazbfmz 0 12133 3372 0
0700011807B50D08 latch: row cache objects IB_RUN cqmgxvb78q9hy 0 17913 6345 0
0700011807B50D08 latch: row cache objects CHANNELAPP byzm159jbjxaa 0 6 19606 52624 0
0700011807B50D08 latch: row cache objects OTHER_CHANNELAPP 2kbjztd9yzqfm 61 0 20732 28687 0
0700011807B50D08 latch: row cache objects CHANNELAPP 6dvagdabts9nx 19 7 21011 504 0
0700011807B50D08 latch: row cache objects CHANNELAPP 9pqrqqfzukrq4 78 0 21439 19030 0
0700011807B50D08 latch: row cache objects CHANNELAPP gq1avu79h2np3 85 0 3815 33831 -1
boesing@mydb4>SELECT child# FROM v$latch_children WHERE addr= '0700011807B50D08';
CHILD#
----------
8
boesing@mydb4> select s.kqrstcln latch#, s.kqrstcid cache#, kqrsttxt name from x$kqrst s where s.kqrstcln=8;
LATCH# CACHE# NAME
---------- ---------- --------------------------------
8 10 dc_users
8 7 dc_users
8 7 dc_users
8 7 dc_users
The problem was definitively solved by applying the 11.2.0.4.2 PSU. No problems after that.
Good luck, if it’s your situation.
Hugs!
Matheus.
