Re: Optimized redo log access

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 .
>
>
>
>
>

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