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Message	Score	Author	Date
Hi all, I want to optimize i/o on my database... ......		Genaro Mendez	Apr 15, 2005
Hi, You can get this information from alert.log......		malay maru	Apr 15, 2005
thanks Malay, from alert.log i can get the sequen......		Genaro Mendez	Apr 15, 2005
Hi, I think ARC always takes the first member o......		Michel Cadot	Apr 15, 2005
As you suspect, "it alternate between the first an......		Yong Huang	Apr 19, 2005
Hi, Never trust anyone, always make your own te......		Michel Cadot	Apr 19, 2005
I agree. You said what I should have said. Anot......		Yong Huang	Apr 19, 2005
Good point. Michel ...		Michel Cadot	Apr 19, 2005
This question was asked before on the Chinese DBA ......		Yong Huang	Apr 19, 2005
Thanks every body, i am going to check the meta......		Genaro Mendez	Apr 19, 2005
Hi, I made a test on Oracle 9.2.0.4/HP-UX with ......		Michel Cadot	Apr 20, 2005

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Subject:	which redolog file member is read
Author:	Genaro Mendez, Costa Rica
Date:	Apr 15, 2005, 1967 days ago
Os info:	Unix
Oracle info:	8.1.7.4
Message:	Hi all, I want to optimize i/o on my database... how to know which redolog member of a group xx the ARCn process read? for example: group 1 redo_01a.log redo_01b.log group 2 redo_02a.log redo_02b.log is allways the member redo_01a.log and redo_02a.log who are read or it may change the next time? I know oracle can read the second member when a read problem happen but it alternate between the first and second member of the same group with no trouble? thanks.
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Subject:	Re: which redolog file member is read
Author:	malay maru, India
Date:	Apr 15, 2005, 1967 days ago
Message:	Hi, You can get this information from alert.log file of your database. Malay
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Subject:	Re: which redolog file member is read
Author:	Genaro Mendez, Costa Rica
Date:	Apr 15, 2005, 1967 days ago
Message:	thanks Malay, from alert.log i can get the sequence and the group number and i want to know the name of group's member. thanks again.
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Subject:	Re: which redolog file member is read
Author:	Michel Cadot, France
Date:	Apr 15, 2005, 1967 days ago
Score:
Message:	Hi, I think ARC always takes the first member of the group but the best way to know that is to put each member of a group on a different disk and iostat the disks under a small workload (for instance with a switch every 10 minutes) then you see which disk ARC read. Regards Michel
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Subject:	Re: which redolog file member is read
Author:	Yong Huang, United States
Date:	Apr 19, 2005, 1963 days ago
Score:
Message:	As you suspect, "it alternate between the first and second member of the same group with no trouble". (How many people have spent hundreds of hours reading Rama Velpuri's under-appreciated backup and recovery book, other than the chapter of case studies? In this case, you can read p.75 of his Oracle8 edition.) Yong Huang
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Subject:	Re: which redolog file member is read
Author:	Michel Cadot, France
Date:	Apr 19, 2005, 1963 days ago
Message:	Hi, Never trust anyone, always make your own tests. This is the only way to get the truth. Btw, the behaviour may change between version. Regards Michel
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Subject:	Re: which redolog file member is read
Author:	Yong Huang, United States
Date:	Apr 19, 2005, 1963 days ago
Score:
Message:	I agree. You said what I should have said. Another way to test is to simply run process trace on ARC process. For instance, on Solaris, we can try truss -t read -p <ARC pid>. The first argument of read() calls shown in output tells you what file it's reading. Combined with pfiles output (or better yet, lsof -p), you know which file it's reading. Yong Huang
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Subject:	Re: which redolog file member is read
Author:	Michel Cadot, France
Date:	Apr 19, 2005, 1963 days ago
Message:	Good point. Michel
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Subject:	Re: which redolog file member is read
Author:	Yong Huang, United States
Date:	Apr 19, 2005, 1963 days ago
Score:
Message:	This question was asked before on the Chinese DBA forum but I didn't do real research. I just searched on Metalink. Note:45042.1 "Archiver Best Practices" has been cited multiple times by Oracle support analysts, particularly the paragraph beginning with Having multiple members to a logfile group is also advisable. If there are multiple members, all members in a group are used to perform the archive process... The note is last revised on 29-OCT-2002 so it may be outdated. However, here's something that really got me interested. In thread 448634.999 in Mar 2003, and thread 370101.995 in May 2003, Melissa Holman questioned about that "round robin" mechanism in normal cases. Basically, she stated the same as Michel, i.e. ARC only reads the first member unless there's an error. Since the conclusion came from the development group, it's hard to disqualify it. She also said it's stated in Admin Guide. Unfortunately, she's the only analyst that says this. Others including Ken Robinson all quote "Archiver Best Practices" without the correction. I'll do some test later and also check Admin Guide. Yong Huang
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Subject:	Re: which redolog file member is read
Author:	Genaro Mendez, Costa Rica
Date:	Apr 19, 2005, 1963 days ago
Message:	Thanks every body, i am going to check the metalink's notes and threads.
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Subject:	Re: which redolog file member is read
Author:	Michel Cadot, France
Date:	Apr 20, 2005, 1962 days ago
Message:	Hi, I made a test on Oracle 9.2.0.4/HP-UX with tusc (ie truss) on 4 switch/archive logs. I had only 1 archiver process to make it easier to trace. 3 log groups with 2 members in each. Conclusion : only the first member is read. The process is the following one (skipping some lines): - receiving a signal on semaphore - writing into alert.log - checking status and opening first member (stat, open, close, open, fcntl) - checking status and opening second member - reading second 1K of first member (lseek, read) - reading second 1K of second member - checking archived log directory and creating archived log - writing into alert.log - reading first 1M after 1K from first member (lseek, read) - writing 1M to archived log - reading next 1M from first member - writing 1M to archived log ... until end of redo log - closing archived log - closing first member - closing second member - writing into alert.log - waiting on semaphore I can send tusc file to each one that is interesting in. Regards Michel
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