Re: Optimized redo log access
Date: Mon, 22 Sep 2014 10:07:41 +0300
Message-ID: <CAKb+SBVJfNFsN3U=FX52KGOKqAzTHdn+G3sUjMejyczTcHkC1w_at_mail.gmail.com>
this feature is applicable only to normal or high redundancy and not external redundancy :(.
On Mon, Aug 18, 2014 at 4:11 AM, K Gopalakrishnan <kaygopal_at_gmail.com> wrote:
> All--
>
> Starting from 12.1 , ASM "Even Read" feature automatically sends the read
> request to least loaded disk groups. So if the OP's objective is to
> distribute evenly , then the functionality is already in the kernel.
>
> -Gopal
>
>
>
>
> On Sun, Aug 17, 2014 at 7:43 PM, Mark W. Farnham <mwf_at_rsiz.com> wrote:
>
>> yeah, ping ponging online redo groups was standard operating procedure
>> back in the day.
>>
>>
>>
>> I think the person asking has members on disks with dramatically
>> differing loads, so he wants arch to use the member on the less busy drive.
>>
>>
>>
>> *From:* oracle-l-bounce_at_freelists.org [mailto:
>> oracle-l-bounce_at_freelists.org] *On Behalf Of *Jeremiah Wilton
>> *Sent:* Sunday, August 17, 2014 4:12 PM
>> *To:* Mark W. Farnham; xiangdongzou_at_gmail.com; 'agonenil'; 'ORACLE-L'
>>
>> *Subject:* RE: Optimized redo log access
>>
>>
>>
>> Amihay pointed out that I probably meant group instead of member.
>>
>>
>>
>>
>>
>> JW
>>
>>
>>
>>
>>
>> Sent from my Verizon Wireless 4G LTE smartphone
>>
>>
>>
>> -------- Original message --------
>>
>> From: Jeremiah Wilton
>>
>> Date:08/17/2014 12:19 PM (GMT-08:00)
>>
>> To: "Mark W. Farnham" , xiangdongzou_at_gmail.com, 'agonenil' , 'ORACLE-L'
>>
>> Subject: RE: Optimized redo log access
>>
>>
>>
>> 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_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.
>>
>> mwf
>>
>> *From:* oracle-l-bounce_at_freelists.org [
>> mailto:oracle-l-bounce_at_freelists.org <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.
>>
>>
>>
>> 2014-08-17
>> ------------------------------
>>
>> *I AM AN ORACLE FANS!*
>>
>> *Skype:Frank.oracle*
>>
>> *Email:xiangdongzou_at_gmail.com <Email%3Axiangdongzou_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 .
>>
>>
>>
>>
>>
>
>
-- http://www.freelists.org/webpage/oracle-lReceived on Mon Sep 22 2014 - 09:07:41 CEST