Re: What is lock type 'KO' in v$lock table?

From: Mladen Gogala <mgogala.spam-me-not_at_verizon.net>
Date: Sat, 23 Sep 2006 02:23:02 GMT
Message-ID: <pan.2006.09.23.02.22.45.151187@verizon.net>

On Fri, 22 Sep 2006 17:38:16 -0700, DA Morgan wrote:

> Bart the bear wrote:

>> Does anyboy know?
>> 
>> 

> I think the SQL statement you are looking for is:
>
> SELECT type, name, description
> FROM v$lock_type
> WHERE type = 'KO';
>
> and it reports back:
>
> KO
> Multiple Object Checkpoint
> Coordinates checkpointing of multiple objects

And there lies the problem: what is checkpointing of objects and when does it occur? The term checkpoint means, when referring to Oracle RDBMS, flushing dirty buffers to database files and it happens on certain occasions, like log switch or every 3 seconds. Judging by analogy, "object checkpoint" would mean flushing dirty buffers for certain segment to the disk. I am also very interested to learn what is it good for, when does it happen and what exactly do KO locks protect? If my assumption is right, "KO enqueue" will lock the entire segment or large parts of it, somewhat like a shared table lock. That cannot be good for concurrency. I smell a mysterious new feature here, which is supposed to improve performance but will be most useful if turned off by using the undocumented parameter mentioned by Charles below. That will probably be a great performance feature in Oracle 11f, the same story as with cache fusion in Oracle 8i: there was a bug which could hang the entire cluster and causing an enormous amount of global waits. Cache fusion is of course, very useful feature of Oracle 9.2 RAC implementations.

-- 
http://www.mgogala.com

Received on Fri Sep 22 2006 - 21:23:02 CDT