You say your log files are on RAID 5?
On a busy database? Are your log files all on the same RAID 5 volume? I'm going to take a SWAG and say that you seriously need to consider dedicating at least 3 RAID 1 volumes to nothing but log file usage. There's a 400-500% write penalty on RAID 5. It's good for reads, not so much for writes. Jared On Thursday 11 July 2002 20:33, chaos wrote: > hi, dbas: > One of the database i manage face a serious wait event, log file sync. > This is a big and busy oltp system, and using disk array of Sun T3 with > raid-5. We are using Veritas QuickIO for datafile and redo log files. The > pressure on the database is growing fast, and more and more the redo log > becomes the bottleneck of the database. Here is some data showing the fact: > > > > 2002/05/03 > Top 5 Wait Events > ~~~~~~~~~~~~~~~~~ Wait % > Total Event Waits Time (cs) > Wt Time -------------------------------------------- ------------ > ------------ ------- log file sync > 82,244 92,442 33.68 db file sequential read > 298,301 80,719 29.41 log file parallel write > 81,849 36,989 13.48 db file parallel write > 5,427 33,615 12.25 control file parallel write > 4,673 6,104 2.22 > > > 2002/05/07 > Top 5 Wait Events > ~~~~~~~~~~~~~~~~~ Wait % > Total Event Waits Time (cs) > Wt Time -------------------------------------------- ------------ > ------------ ------- log file sync > 6,352,383 15,785,313 40.09 db file sequential read > 26,862,699 12,538,922 31.85 log file parallel write > 5,971,229 3,990,066 10.13 db file parallel write > 290,479 3,164,391 8.04 db file scattered read > 1,749,137 814,981 2.07 > > 2002/05/21 > Top 5 Wait Events > ~~~~~~~~~~~~~~~~~ Wait % > Total Event Waits Time (cs) > Wt Time -------------------------------------------- ------------ > ------------ ------- log file sync > 2,207,609 6,688,751 59.47 log file parallel write > 2,044,977 1,385,379 12.32 db file parallel write > 103,155 1,203,077 10.70 db file sequential read > 8,772,908 1,088,922 9.68 log buffer space > 3,284 222,604 1.98 > > 2002/05/28 > Top 5 Wait Events > ~~~~~~~~~~~~~~~~~ Wait % > Total Event Waits Time (cs) > Wt Time -------------------------------------------- ------------ > ------------ ------- log file sync > 2,247,585 20,529,779 63.71 db file parallel write > 441,052 4,377,899 13.59 log file parallel write > 1,724,089 3,806,535 11.81 db file sequential read > 8,854,525 2,044,020 6.34 enqueue > 78,759 592,411 1.84 > > 2002/07/04 > Top 5 Wait Events > ~~~~~~~~~~~~~~~~~ Wait % > Total Event Waits Time (cs) > Wt Time -------------------------------------------- ------------ > ------------ ------- log file sync > 3,838,694 13,158,371 63.28 db file sequential read > 2,189,863 2,401,275 11.55 log file parallel write > 3,401,035 2,098,018 10.09 db file parallel write > 97,086 1,503,608 7.23 enqueue > 71,251 432,706 2.08 > > 2002/07/11 > Top 5 Wait Events > ~~~~~~~~~~~~~~~~~ Wait % > Total Event Waits Time (cs) > Wt Time -------------------------------------------- ------------ > ------------ ------- log file sync > 453,862 9,679,513 68.11 db file sequential read > 500,157 1,660,982 11.69 db file parallel write > 67,235 1,137,017 8.00 log file parallel write > 163,180 1,075,201 7.57 log file sequential read > 32,012 254,327 1.79 > > > > > As you can see, log file sync is a big bottleneck, and i have to solve this > problem. I think the best solution maybe convert to dedicated raid1 or > single disk with oracle multiplex, but this need to rebuild the whole disk > array , need too much downtime, and with some risk. I tried to disable > CachedQuick IO on the redo log file, but did not see performance gains. > Veritas Said quick io is as fast as RAW, but i did not tested it before, i > wonder whether move to raw for redo log will helps? It is difficult to > modify the application to reduce the frequency of commit, for every > transaction finishes, it have to commit. > > Another strange question is that: from the iostat result and sar -d result, > there is not much write to the disk array, maybe 2Mbytes/second, and it > causes so much wait( average 10%time wait during normal workload). Maybe > some misconfiguration in the disk array? Thanks for everyone reading and > answering, please give me some suggestions > > > > > Good luck! > > chaos > [EMAIL PROTECTED] > > zhu chao > DBA of Eachnet.com > 86-021-32174588-667 -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Jared Still INET: [EMAIL PROTECTED] 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: [EMAIL PROTECTED] (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).
