Re: Deleting large table and the correct log buffer size

From: Alexandre Gorbatchev <alexandre.gorbatchev_at_avermann.de>
Date: Wed, 26 Jun 2002 10:30:17 -0800
Message-ID: <F001.004890BF.20020626103017@fatcity.com>

Vasu,

I think you should increase the size of your redo log files to make log switches at average once every 10-30 mins.

I wouldn't make redo log buffer more than several Megs. Alexandre

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Wednesday, June 26, 2002 6:49 PM

> 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
>

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-- 
Author: Alexandre Gorbatchev
  INET: alexandre.gorbatchev_at_avermann.de

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Received on Wed Jun 26 2002 - 13:30:17 CDT