Re: Sudden Backup Slowdown

From: Mladen Gogala <gogala.mladen_at_gmail.com>
Date: Tue, 5 Nov 2019 07:13:21 -0500
Message-ID: <442d794c-7af3-a5ad-e992-37f97ba03e07_at_gmail.com>



Hi Charlotte!

What kind of a channel do you allocate, disk or SBT? If SBT, what kind of backup suite are you using? Stuff like NetBackup, Commvault or TSM is highly complex and dependent on may factors.

Regards

On 11/5/19 3:27 AM, Charlotte Hammond (Redacted sender charlottejanehammond for DMARC) wrote:
> Hi Nenad,
>
> The average run queue is about 20 (peaking at about 25) whilst the
> backup is running.   The figure is the same for both the slow and fast
> runs.   I've graphed them out and they look pretty much the same.  
> This is a fairly high figure but it doesn't seem to have changed.
>
> We have 16 backup channels and 16 CPUs (2 threads per processor).
>
> Yes, the compression is "basic" but that has not changed.
>
> Thanks,
> Charlotte
>
>
>
>
> On Monday, November 4, 2019, 09:26:33 PM GMT, Noveljic Nenad
> <nenad.noveljic_at_vontobel.com> wrote:
>
>
> Hi Charlotte,
>
> Run queue length of 20-25 means the number of processes competing for
> CPU.
>
> How many CPUs do you have? How many RMAN channels are configured?
>
> What was the average length of run queues during a good run?
>
> With regard to backup compression, basic will use significantly more
> CPU than the others, but as you mentioned that the backup size is the
> same, the backup algorithm probably hasn‘t changed.
>
> I‘d therefore suggest first clarifying the CPU load on the server.
>
> Best regards,
>
> Nenad
>
>
>
> *Von: *Charlotte Hammond <charlottejanehammond_at_yahoo.com
> <mailto:charlottejanehammond_at_yahoo.com>>
> *Datum *Montag, 04. Nov. 2019, 6:15 PM
> *An: *dmarc-noreply_at_freelists.org <dmarc-noreply_at_freelists.org
> <mailto:dmarc-noreply_at_freelists.org>>, ORACLE-L
> <oracle-l_at_freelists.org <mailto:oracle-l_at_freelists.org>>, Noveljic
> Nenad <nenad.noveljic_at_vontobel.com <mailto:nenad.noveljic_at_vontobel.com>>
> *Betreff: *Re: Sudden Backup Slowdown
>
>
> Hi Nenad,
>
> The only real difference between the AWR reports is that the statistic
> "RMAN cpu time (backup/restore)" is about 50% longer than before.  Sar
> shows the run queues as 0 (or close to 0) before and after the backup
> in both cases and similar during the backup (about 20-25).
>
> Thanks,
> Charlotte
> On Monday, November 4, 2019, 02:51:38 PM GMT, Noveljic Nenad
> <nenad.noveljic_at_vontobel.com> wrote:
>
>
> If there weren’t any idle CPUs during backup, I’d first verify the
> statement “The server itself has no other activity during the backup
> window.” by measuring the length of the run queues. In other words, to
> confirm there aren’t any other processes competing for CPUs.
>
> What differences do you see in AWR reports?
>
> Best regards,
>
> Nenad
>
> https://nenadnoveljic.com/blog/
>
> *From:*oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org>
> *On Behalf Of *Charlotte Hammond
> *Sent:* Montag, 4. November 2019 15:22
> *To:* ORACLE-L <oracle-l_at_freelists.org>
> *Subject:* Sudden Backup Slowdown
>
> Hello All,
>
> I'm trying to explain why my level 0 rman backups have suddenly jumped
> from 8hours to 12 hours.  The size of the backup has barely changed
> and there has been no configuration changes.  AWR and O/S statistics
> show that CPU for all the channels are maxed out at ~99% (presumably
> backup compression) for most of this time, both in the 8 hour case and
> 12 hour case. The server itself has no other activity during the
> backup window.
>
> This is on 11.2.0.4 on AWS EC2 backing up to S3 storage.
>
> I'm not looking for tuning advise here (thanks though!) - I'm really
> hoping for some advise on finding an explanation for the change in
> times.  Given that all it's doing is sitting on CPU I'm not sure what
> else I can investigate - especially with limited ability to
> cross-reference it with the "good old" runs.   It's been 8 hours for
> months and months, and has now been 12 hours for the last 3 weeks.  
> There was no gradual increase - just a step change.
>
> Thanks!
>
> Charlotte
>
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-- 
Mladen Gogala
Database Consultant
Tel: (347) 321-1217



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Received on Tue Nov 05 2019 - 13:13:21 CET

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