Oracle-L: RE: Deleting large table and the correct log buffer size

From: Kevin Lange <kgel_at_ppoone.com>
Date: Wed, 26 Jun 2002 12:58:41 -0800
Message-ID: <F001.004895B6.20020626125841@fatcity.com>

WE had a similar bad response when deleting from a 16 million row table. Due to certain circumastances we were unable to truncate ... only delete.

We found 2 things that caused the big slowdown.

Archiving. Logging all the delete added a small amount of slowdown.
Extents. It turned out that table had 8540 extents (I know ... it was one reason were were rebuilding it). That many extents causes a very big strain on things.

We ended up rebuilding it twice. The first time , the delete litterally took hours. The second time (After the extent problem was taken care of), the delete took minutes.

I am curious as to how many extents that table has.

-----Original Message-----
Sent: Wednesday, June 26, 2002 3:35 PM
To: Multiple recipients of list ORACLE-L

Hi Jared,

Our developers are expecting it to be equivalent Sybase response time which is less than 2 minutes. We are
moving from Sybase to Oracle. But Oracle beats Sybase response time in all other SQL queries. I was trying to see
whether any incorrect init params are set.

Thanks

Vasu

Jared.Still_at_radisys.com wrote:

> Personally, I'd be pretty happy with a 400K row delete
> only taking 10 minutes.
>
> Jared
>
> "Vasu Ramasamy" <vasu.ramasamy_at_sri.com>
> Sent by: root_at_fatcity.com
> 06/26/2002 09:49 AM
> Please respond to ORACLE-L
>
>
> To: Multiple recipients of list ORACLE-L
<ORACLE-L_at_fatcity.com>
> cc:
> Subject: Deleting large table and the correct log buffer
size
>
> Hello Gurus,
> Ours is basically a Sybase shop. But moving towards Oracle. We are in
> the process of conversion. I have a problem in deleting a large number
> of rows. To delete 400,000 rows approx., it takes nearly 10 minutes to
> complete and sometimes hogs system. It is a simple delete statement,
> delete all rows. We do not want to use truncate statement. I try to find
> why it is taking so much time by checking the wait events. The session
> event wait statistics is provided below.
>
> SIDEVENT
> TOTAL_WAITS TOTAL_TIMEOUTS TIME_WAITED
>

>
> AVERAGE_WAIT MAX_WAIT
> ----------------------
> 27latch
> free
> 10 10 20
> 2 2
>
> 27log buffer
> space
> 298 271 29267
> 98.2114094 104
>
> 27log file switch
> completion 11
> 10 1069
> 97.1818182 103
>
> 27log file
> sync
> 3 2 221
> 73.6666667 103
>
> 27db file sequential
> read 3222
> 0 7695
> 2.38826816 589
>
> 27db file scattered
> read 271
> 0 493
> 1.81918819 236
>
> 27file
> open
> 4 0 0
> 0 0
>
> The log_buffer_space wait event looks like is the culprit with
> total_wait =298, total_timeout = 271, and time_waited = 29267 ( 1/100th
> of a second). Are these normal values for this wait event? The log
> buffer init param is set to 20MB. To set up the init params, we took the
> advice of the consultant DBA who worked for a short time (6 months) to
> help us to set up servers. While I was going through the DBA hand books,
> ( 101 Oracle performance tuning by gaja krishna vaidyanatha and other)
> it clearly says that setting higher value will cause trouble. He
> recommends to set it to 1MB. I tried with 4MB log buffer, the wait stats
> for log_buffer_space just doubles.
>
> Can you please advice me what should be the correct size for log
> buffer?
> Do you see any problem with wait stats provided above?
>
> If you need further details, let me know please.
>
> Thanks
>
> Vasu

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Kevin Lange
  INET: kgel_at_ppoone.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).

Received on Wed Jun 26 2002 - 15:58:41 CDT