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Initial Parameter DB_WRITER_PROCESSES Doesn't work

-0001-11-30   Views:0

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I set the initial parameter DB_WRITER_PROCESSES as 5 in init.ora file. But when I restarted the database, I found the parameter show as 1 and only DBW0 existed. I don't know the reason, would you please help me? Thanks and Best Regards, Su QianDid yo

I set the initial parameter DB_WRITER_PROCESSES as 5 in init.ora file. But when I restarted the database, I found the parameter show as 1 and only DBW0 existed.
I don't know the reason, would you please help me?
Thanks and Best Regards,
Su Qian

The replay answer
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Did you get a message in the alert log about starting dbwr processes failed?No, I havn't gotten the message.
Also, having multiple writers on a single cpu system could bring performance down. I think one rule of thumb is to have 4 cpus per writer.Thanks for your message. I will not re-set the parameter.
First, I'd like to let you know that the environment of my production database are as follows:
OS: HP-UX
Database Version: Oracle8 Enterprise Edition Release 8.0.4.2.1 - Production
The setting of DB Block: 2K
The main problem I come across is when running application the response speed of DB is very slow.
The first step I adopted was checking free space. After checking I thought it was sufficient. But when I adopted the second step checking v$system_event, I found the wait time of following events is high.
EVENT TOTAL_WAITS TOTAL_TIMEOUTS TIME_WAITED AVERAGE_WAIT
db file parallel write 471 1 128370 272.547771
log file parallel write 30307 0 51440 1.69729765 (For reference)
pmon timer 37189 36806 11111071 298.773051
rdbms ipc message 142737 112253 66295957 464.462312
rdbms ipc reply 296 0 7167 24.2128378
smon timer 372 369 11082933 29792.8306
write complete waits 75 37 5149 68.6533333
According to the above message, I decided to tune I/O first. Is my thought right?
If dbwr is rather slow, these events should give som hints: free buffer waits, rdbms ipc reply, log file switch (checkpoint incomplete).Yes, when I had a look at the alert.log I found the error message: checkpoint incomplete. So I created a new log group.Perhaps the problem was too few log groups and not dbwr. If you do not have high free buffer waits dbwr should be ok :)I agree with you. I havn't high free buffer waits, so the main problem could be too few log groups. But I don't understand two points as follows.
1. Last Friday I had 4 log groups and the size of every group is 2M. when getting the message "Thread 1 cannot allocate new log, sequence 87816 Checkpoint not complete", I created a new log group of 2M. Normally, this operation should improve performance, but when I observed the statistics I found the average wait time of "db file parallel write" became more longer. (Please refer to the following list)
EVENT TOTAL_WAITS TIME_WAITED AVERAGE_WAIT DATE LOG_GROUPS
db file parallel write 471 128370 272.547771 2002-08-05 5
db file parallel write 798 88568 110.987469 2002-08-03 4
2. I think the shortage of log groups is caused by the archive of log group don't complete before overwirting. From the alert.log file I found the time of log switch is about 20 minutes. From my viewpoint 20 minutes is enough for log archive. Why is the log groups still short?
In addition, according to the setting of checkpoint parameters I think the checkpoint should occur only at the time of log switch.
NAME TYPE VALUE
db_block_checkpoint_batch integer 8
log_checkpoint_interval integer 1000000
log_checkpoint_timeout integer 0
db_block_max_dirty_target integer 4294967294
db_block_buffers integer 153600 (For reference)
Do you know the meaning db_block_checkpoint_batch? (I can't find it in the document of 8i, because it is obsoleted.)
From the alert.log file, I got the following errors.
1. Fri Aug 2 17:10:36 2002
Errors in file /lims/oradata/lab1/udump/ora_10976.trc:
ORA-00600: internal error code, arguments: [1237], [], [], [], [], []
(I got the error message occasionally.)
2. Fri Aug 2 16:57:37 2002
ORA-1652: unable to extend temp segment by 256 in tablespace TEMP
(I don't understand it clearly, because the size of temporary tablespace is 400M. I think it is large enough.)     
3. Fri Jul 26 12:00:17 2002
Thread 1 cannot allocate new log, sequence 87816
Checkpoint not complete
Current log# 1 seq# 87815 mem# 0: /u02/oradata/lab1/db/redolab101.log
Looking forward your reply.
Thanks and Best Regards,
Su Qian

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