RE: Redo latch contention

From: Christopher Spence <cspence_at_FuelSpot.com>
Date: Sat, 16 Jun 2001 09:35:33 -0700
Message-ID: <F001.0032C74E.20010616092019@fatcity.com>

Setting it too high may cause additional content switching.

"Walking on water and developing software from a specification are easy if both are frozen."

Christopher R. Spence
Oracle DBA
Fuelspot

-----Original Message-----
Sent: Saturday, June 16, 2001 4:26 AM
To: Multiple recipients of list ORACLE-L

Hi All,

I had some situation of Redo Allocation and copy latch contention as stated in following output.....

SQL> SELECT substr(NAME,1,18) NAME, GETS,MISSES, IMMEDIATE_GETS, IMMEDIATE_MISSES
FROM V$LATCH WHERE NAME LIKE '%redo%'
/

NAME                     GETS     MISSES IMMEDIATE_GETS IMMEDIATE_MISSES

------------------ ---------- ---------- -------------- ----------------

redo allocation         74878         16              0                0

redo copy                 114        100          53756              232

redo writing            30219          1              0                0

3 rows selected.

Realizing small contention on redo allocation latch, I increased the value of "log_small_entry_max_size" from 80 to 90.

But this would definitely overload (already suffering) redo copy latches, so I increased the value of log_simultaneous_copies from 2 to 6.

This sorted out redo latch contention, but somewhere in FM it's mentioned that value of log_simultaneous_copies shouldn't be more than (2 * #_of_CPUs). Again I know that the CPU is "not" heavily used so far. So...

Is it OK to set log_simultaneous_copies higher than 2*CPU. What are the golden rules. I have seen some authers not mentioning this.
Why this parameter is missing from Oracle 8i?? Has Oracle changed the algorithm?? What is the new strategy to handle redo latch contention??

Interestingly, in Oracle 8i (Oracle 8.1.6) Tuning Manuals they still talk of these parameters(which are made obsolete)...

Appreciate your inputs ;-)

Cheers,
Rajesh
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Author: Rajesh Dayal
INET: Rajesh_at_ohitelecom.com

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Author: Christopher Spence
INET: cspence_at_FuelSpot.com

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