RE: Optimized redo log access
Date: Sun, 17 Aug 2014 13:54:05 -0700
Message-ID: <BLU179-W4E452126A74FAB6DF01BBEBD70_at_phx.gbl>
There ought to be a way to have the storage perform the duplication of the redo logs to the archive destination instead of performing a file copy. But if wishes were horses, I would ride. Iggy
Date: Sun, 17 Aug 2014 12:19:14 -0700
Subject: RE: Optimized redo log access
From: jcwilton93_at_earlham.edu
To: mwf_at_rsiz.com; xiangdongzou_at_gmail.com; agonenil_at_gmail.com; oracle-l_at_freelists.org
Back when it mattered which disk device we accessed for a specific operation, this was pretty easy to achieve.
You just alternate disk(s) by member. For instance, if you have two dedicated disks for online logs, member 1 would be on disk A and member 2 on disk B. That way when we switch from member 1 to member 2, the archiver reads from disk 1 while we write to the online log on disk 2. You can see easily how we could even do this and keep multiplexing with 4 disks.
I doubt that you get much benefit trying to do this kind of thing on modern storage.
Jeremiah
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- Original message --------From: "Mark W. Farnham" Date:08/17/2014 6:13 AM (GMT-08:00) To: xiangdongzou_at_gmail.com, 'agonenil' , 'ORACLE-L' Subject: RE: Optimized redo log access
I also do not know a way to make the archiver read a preferred member.However, you may be able to get the read from a preferred physical disk depending on your volume manager.In ASM this would be by setting (or your preference being the default) the asm preferred read failure group as shown in this example from the manual so that your preferred read is the first one:alter system set asm_preferred_read_failure_groups = 'DG2.DG2_0000','DG3.DG3_0000'In some other volume managers there are possibilities for influencing or controlling the preferred read of a volume constructed from plexes on different physical media.The starting point recommendation for multiple members is they should be on media of similar capabilities and load, so the archiver (unless they slipped it in when I wasn’t paying attention) does not directly have a toggle for preference by member.)Good luck. (Of course feeding arch is the reason some folks put redo on SSD, while benchmarkers run around “debunking” the idea of redo on SSD because they can show it does not speed up writes to compared to isolated physical HD volumes when they compare to flash SSD [not battery backed DRAM SSD] with arch turned off.) Removing arch reads from your diskfarm by relocating redo to SSD will in fact “deheat” your disk farm and remove the competition for seeks for writes and bandwidth for arch reads. Since redo is usually small relative to the database disk farm, this may be cost effective, depending on your situation.mwfFrom: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of xiangdongzou
Sent: Sunday, August 17, 2014 5:27 AM
To: agonenil; ORACLE-L
Subject: 回复: Optimized redo log access archiver process can't read only special member.Oracle decicde which member shoulde read. 2014-08-17I AM AN ORACLE FANS!Skype:Frank.oracleEmail:xiangdongzou_at_gmail.com发件人：amihay gonen <agonenil_at_gmail.com>发送时间：2014-08-17 16:51主题：Optimized redo log access收件人："ORACLE-L"<oracle-l_at_freelists.org>抄送： Hi , I've system that have multiplex redo log (2 members per group) and multiplex destinations . Due to performance consideration I would like to configuration the archiver process to read only from one member (to reduce load on the specific device). I'm not aware of such option to tell oracle which member to read .Does anyone know if it is possible ? Amihay .
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