Re: Deleting large table and the correct log buffer size

Hi kirti,

    My responses are embedded in your message.

   Thanks

Vasu

"Deshpande, Kirti" wrote:

> Are the disks housing redo logs contain other 'hot' files? Are these disks
> busy with other tasks (than writing redo logs).

      No. Though there are db files in its disks, they are not that active. More over, the server where I perform this test is totally quiet.

> Are you committing too
> often?

    No. There is only one commit after the delete statement.

> How many log switches are taking place?

     10 or 11 switches

> What is the size of the redo
> log file?

     100MB

> May be increasing it may help.
>
> What is the redo size per commit?
> Use this query to find out RSPC:
> select r.value / decode (c.value, 0, 1, c.value) RSPC
> from v$sysstat r, v$sysstat c
> where r.name = 'redo size'
> and c.name = 'user commits';
> You can use RSPC to size log buffer by multiplying it by number of user
> commits per second.
>

    1104361.8003

>
> HTH,
>
> - Kirti
>
> -----Original Message-----
> Sent: Wednesday, June 26, 2002 11:49 AM
> To: Multiple recipients of list ORACLE-L
>
> 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: Deshpande, Kirti
> INET: kirti.deshpande_at_verizon.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Vasu Ramasamy
  INET: vasu.ramasamy_at_sri.com

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