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Oracle backup consumig excessive CPU time

 
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Randy Navarro_1
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Oracle backup consumig excessive CPU time

We run a nightly hot backup and we're seeing CPU available free time drop dramatically from 75% to 10% or even hit zero.

The backup includes copying tablespace datafiles to a backup area on our RAID. Then the data is written to tape. It is the first part of writing to the backup area that loads the CPU excessively. Once the write to tape step begin, we see CPU loading reduced and returned to normal upon completion.

We've tried using 'nice' for process prioritization, but that hasn't helped much.

System Info:
HP-UX 10.20
HP K420
Oracle 7.3.2.2
17 REPLIES 17
LucianoCarvalho
Respected Contributor
Solution

Re: Oracle backup consumig excessive CPU time

hi,

I think the problem could be the disks with high utilization during backup. Have you monitored the disks with "sar -d" or glance?
If the utilization are very high, will be necessary to divide the lod between many disks, maybe using disk stripe.

regards
Paula J Frazer-Campbell
Honored Contributor

Re: Oracle backup consumig excessive CPU time

Randy

Instead of a copy for each backup why not mirror the backup area to the data and then split it away at backup time and merge back in when finished.

Ps the database may need to be stopped/synced during the split away to ensure file integrity.





Paula
If you can spell SysAdmin then you is one - anon
Michael Steele_2
Honored Contributor

Re: Oracle backup consumig excessive CPU time

What backup utility? What RAID utility? What lun configuration on the RAID and what level of RAID?

Check for bottlenecks during this window and attach:

sar -u 5 5
sar -d 5 5
vmstat 5 5
sar -v 5 5
swapinfo -tam
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Randy Navarro_1
New Member

Re: Oracle backup consumig excessive CPU time

Paula,

Could you elaborate on breaking a mirrored pair of drives? Can the primary mirrored drive still stay active while we work with the second drive to backup data? And, what would be the performance cost in reestablishing the mirrored pair?

Thanks all for your assistance.
Paula J Frazer-Campbell
Honored Contributor

Re: Oracle backup consumig excessive CPU time

Randy

When breaking a mirror it depends upon your data being stored, as if active there is a possiblity of an incomplete record write.

Most databases have a lock command which will hold the database during the mirror split (this should take less than a second.)

Then as soon the split has occured then it can be unlocked - most users would be unaware that a split had occured.

On my database I have a triple mirror which I split away one to backup whilst live.

It is a very safe way on a database that must be available 25/7/365.

The best way is to script the split and restore into your backup routine echoing time and date into a log file :-

echo " Start time" > /tmp/mirror.log
date > /tmp/mirror.log
"database hold command"
lvsplit "lvol"
fbackup command
lvmerge "lvol"
echo " End time" > /tmp/mirror.log
date > /tmp/mirror.log.


Test it fully on a sandbox (Play) server.



Paula
If you can spell SysAdmin then you is one - anon
malay boy
Trusted Contributor

Re: Oracle backup consumig excessive CPU time

Hi,
I agree with Paula.That's how we backup our database which are mirrored.This are the step that we take :

1) stop the database
2) split the mirror
3) bring up database without mirror
4) backup the mirror
5) after finish backup,mirror back the database.


regards
mB
There are three person in my team-Me ,myself and I.
twang
Honored Contributor

Re: Oracle backup consumig excessive CPU time

I would suggest break the mirror first, then back to the backup and try again, you should also open a session to monitor the OS process using "top" and see what consuming the CPU time.
Michael Steele_2
Honored Contributor

Re: Oracle backup consumig excessive CPU time

How do you perform an LVM mirror split on a RAID disk array?

Could you attach or check your lvdisplay please. Is the value of mirror 0, 1, 2?

Are there BCV's involved on this disk array? Hot backups with a BCV don't include an LVM mirror split.

How are splitting mirrors going to remove a CPU bottleneck which is defined as 0% CPU idle + higher then usual process level + more than one job waiting in the run queue?

I apologize if I've missed something but I think we've taken a wrong turn somewhere.

And I renew my request to evaluate your system with the 'sar' commands attached above.
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Paula J Frazer-Campbell
Honored Contributor

Re: Oracle backup consumig excessive CPU time

Hi Michael


My logic is that trying to backup a live database will cause problems as the disks will be very busy with the backup routine and the users both trying to access files, so it you split away a seperate area that only the backup routine is using then the load generated by this heavy disk usage will be reduced.

BTW the log commads should use >> and not >

Paula
If you can spell SysAdmin then you is one - anon