Re: Higher CPU Utilisation on failover node under same workload

From: De DBA <dedba_at_tpg.com.au>
Date: Thu, 06 Nov 2014 11:44:16 +1000
Message-ID: <545AD270.3020701_at_tpg.com.au>

I guess that this is an active dataguard setup where one node goes down for patching? Did you defer the archive logging while performing the OS patching on the node that is down? If not, the failed over system may spend much time attempting to archive logfiles to that node. The alert log would contain many timeout messages in this case.

A look at top/prstat/etc. may yield some pointers as to which process exactly spends so much CPU time in kernel mode.

Cheers,
Tony

On 05/11/14 23:20, Osborne, Chris wrote:
> Hi all,
>
> This is my first post.
>
> I have an ongoing issue where I am seeing much increased CPU utilisation when a database is running on the failover node, compared to when it is running on the primary node.
> When we perform OS patching we fail from one node to the DR site, while the primary site is being patched.
> Both hosts are the same spec and config, and the database is configured identically on both hosts too.
>
> AWR Diff reports show that the workload is very similar.
>
> The 2nd period is where we see the problem
>
>
> 1st 2nd
> ------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------
> Event Wait Class Waits Time(s) Avg Time(ms) %DB time Event Wait Class Waits Time(s) Avg Time(ms) %DB time
> ------------------------------ ------------- ------------ ------------ ------------- ----------- ------------------------------ ------------- ------------ ------------ ------------- -----------
> db file sequential read User I/O 4,178,196 23,392.4 5.6 61.7 CPU time N/A 38,985.7 N/A 59.8
> CPU time N/A 10,138.9 N/A 26.8 db file sequential read User I/O 4,581,489 23,083.5 5.0 35.4
> read by other session User I/O 325,114 1,866.3 5.7 4.9 db file parallel read User I/O 219,007 1,670.0 7.6 2.6
>
> db file parallel read User I/O 177,766 1,419.6 8.0 3.7 read by other session User I/O 246,088 1,307.7 5.3 2.0
> enq: TX - row lock contention Application 1,220 1,321.2 1083.0 3.5 enq: TX - row lock contention Application 651 618.6 950.2 0.9
> --------------------------------------------------------------------------------------------------------------------
>
>
> Host Configuration Comparison
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 1st 2nd Diff %Diff
> ----------------------------------- -------------------- -------------------- -------------------- ---------
> Number of CPUs: 256 256 0 0.0
> Number of CPU Cores: 32 32 0 0.0
> Number of CPU Sockets: 4 4 0 0.0
> Physical Memory: 261632M 261632M 0M 0.0
> Load at Start Snapshot: 32.61 57.98 25.37 77.8
> Load at End Snapshot: 33.13 63.91 30.78 92.9
> %User Time: 6.03 4.95 -1.07 -17.9
> %System Time: 4.82 15.19 10.37 215.1
>
> %Idle Time: 89.15 79.86 -9.29 -10.4
> %IO Wait Time: 0 0 0 0.0
> Cache Sizes
>
> I know that we have a problem with the size of the connection pools on this database, and the fact that they are dynamic too concerns me. This issue is being worked on.
> My first thought is that fact that the single block read time is 10% faster could be meaning more of the sessions are runnable at any given point and slowing us down through context switching, but this may be a stretch...
> I am seeing the host reporting more CPU time spent on SYS rather than User time though.
>
> Any advice/pointers would be gratefully received.
>
> Cheers
>
> Chris
>
>
> Christopher Osborne
>
>
>
>
>
>
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Received on Thu Nov 06 2014 - 02:44:16 CET