Re: Deleting large table and the correct log buffer size

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

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