RE: Optimized redo log access
- From: Iggy Fernandez <iggy_fernandez@xxxxxxxxxxx>
- To: 'ORACLE-L' <oracle-l@xxxxxxxxxxxxx>
- Date: Sun, 17 Aug 2014 13:47:54 -0700
Nobody got fired for agreeing with Jeremiah :-)
We assume that we are working with separate disks but most of the time,
everything is on the same SAN or NAS and the storage is only logically separate
and everything comes does the same network pipe.
Channeling Gaja Krishna Vaidyanatha of Compulsive Tuning Disorder fame and Cary
Millsap of Method-R fame, I would like to see proof that the archiver is
causing the performance problem and an estimate of how much improvement would
result from having the archiver read only from one member.
And, channeling Tom Kyte, "why?" is probably the best answer in this case.
Iggy
Date: Sun, 17 Aug 2014 12:19:14 -0700
Subject: RE: Optimized redo log access
From: jcwilton93@xxxxxxxxxxx
To: mwf@xxxxxxxx; xiangdongzou@xxxxxxxxx; agonenil@xxxxxxxxx;
oracle-l@xxxxxxxxxxxxx
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
Sent from my Verizon Wireless 4G LTE smartphone
-------- Original message --------From: "Mark W. Farnham" Date:08/17/2014
6:13 AM (GMT-08:00) To: xiangdongzou@xxxxxxxxx, '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@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] 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@xxxxxxxxx发件人：amihay gonen
<agonenil@xxxxxxxxx>发送时间：2014-08-17 16:51主题：Optimized redo log
access收件人："ORACLE-L"<oracle-l@xxxxxxxxxxxxx>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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