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@xxxxxxxxxxxx> 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@xxxxxxxxx>Datum Montag, 04. Nov.
2019, 6:15 PMAn: dmarc-noreply@xxxxxxxxxxxxx <dmarc-noreply@xxxxxxxxxxxxx>,
ORACLE-L <oracle-l@xxxxxxxxxxxxx>, Noveljic Nenad
<nenad.noveljic@xxxxxxxxxxxx>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,CharlotteOn Monday, November 4, 2019, 02:51:38 PM GMT, Noveljic Nenad
<nenad.noveljic@xxxxxxxxxxxx> wrote:
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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@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx>On Behalf Of
Charlotte Hammond
Sent: Montag, 4. November 2019 15:22
To: ORACLE-L <oracle-l@xxxxxxxxxxxxx>
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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