RE: SMON - Does it cause a degrade?

From: <Rajesh.Rao_at_chase.com>
Date: Fri, 25 Jan 2002 15:49:04 -0800
Message-ID: <F001.003FBEC1.20020125154527@fatcity.com>

Thanks Melissa. I was wrong, I guess. For this is what I found on Metalink.

Because SMON acquires the Space Transaction (ST) enqueue in exclusive mode, other processes requiring the enqueue will be blocked. This is typically manifested by multiple <oerr:ORA-1575> errors.
SMON sits in a very tight loop while coalescing, and consumes close to 100% CPU. If the system is CPU-bound, the run queue will increase as other processes try to get onto CPU.

Regards
Raj

"Godlewski, Melissa" <Melissa.Godlewski_at_hq.doe.gov>@fatcity.com on 01/25/2002 05:20:20 PM

Please respond to ORACLE-L_at_fatcity.com

Sent by: root_at_fatcity.com

To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> cc:

Check out meta link note:61997.1 SMON - Temporary Segment Cleanup and Free Space Coalescing. For one explanation.

-----Original Message-----

Sent: Friday, January 25, 2002 4:50 PM
To: Multiple recipients of list ORACLE-L

Hey Fellas,

I have an application DBA who insists that the pctincrease at the data tablespace should be set to 0 so that SMON does not coalesce the tablespace. He says coalesce will be performed by using a scheduled batch job written for that purpose. He states that having SMON to perform an coalesce of the tablespace could cause an performance degrade??? I have never heard of such a thing, but then I dont wanna argue with him. He's got wrinkles on his face, and grey hair ;-)

My argument would be, go back to the drawing board, get your tables sized properly, if you anticipate fragmentation. And SMON does not cause a performance degrade? It wakes up every 5 minutes, does hold ST enqueue locks if a tablespace needs coalescing, but it does not cause a performance degrade? Or does it???

Now, can I have a definitive word on this? Any sites, white papers, to refer to that says so, or to the contrary. I need to convince the higher ups.

Raj

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