RE: Log File Syncs

Fair point. I guess I was focusing on how a log file sync wait can be shorter than the log file parallel write which it is waiting on. Both DB’s are on XIV storage

The log file write time is also slightly faster on the ‘slow’ DB leading me to believe that IO is not an issue.

CPU wise, the VM has 2vCPU’s
model name : Intel(R) Xeon(R) CPU E5-2680 v3 _at_ 2.50GHz the physical has
12 cores with hyper threading
model name : Intel(R) Xeon(R) CPU E5-2620 0 _at_ 2.00GHz

The VM has 4GB of memory

The physical has 64GB.

Regards,

Chris

Christopher Osborne
Lead Technical Specialist, Performance Engineering, OE Infrastructure Ops Scotland

Sky UK
Email:chris.osborne_at_sky.uk
Desk: +44 1506 325069 | Mobile: +44 7720 308941

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From: Andrew Kerber [mailto:andrew.kerber_at_gmail.com] Sent: 24 March 2016 16:47
To: Osborne, Chris <Chris.Osborne_at_sky.uk> Cc: oracle-l_at_freelists.org
Subject: Re: Log File Syncs

the obvious question is what is the underlying hardware? All you have told us is that we have a physical server and a virtual server.

Sent from my iPhone

On Mar 24, 2016, at 8:58 AM, Osborne, Chris <Chris.Osborne_at_sky.uk<mailto:Chris.Osborne_at_sky.uk>> wrote: Hi All,

I was wondering if someone could maybe help me out with an unusual observation I have on a couple of test systems. I have a user reporting that they are seeing differences in performance between the database on a VM (which is running ‘fast’) and a database on a physical (which is running slow)

They are performing a load from MongoDB via a PHP app into the oracle database. In both tests the same source database is being used.

I’ve done a quick overview on each of the systems and the only thing that is jumping out at me is that on the faster DB the log file sync time is much lower on the faster one. (the output was gather using oratop) Both DB’s are 12.1.0.2. The faster one is on CentOS 6.6 and the Slower one on Redhat 5.11.

Slow DB

EVENT     (Real-Time)       AVG: TOT WAITS  TIME(s)  AVG_MS PCT  WAIT_CLASS
log file parallel write           20008284    23783     1.2 100  System I/O
log file sync                         1730        9     5.2   0  Commit
DB CPU                                            0           0


Fast DB
EVENT     (Real-Time)       AVG: TOT WAITS  TIME(s)  AVG_MS PCT  WAIT_CLASS
log file parallel write           20389439    28216     1.4 100  System I/O
log file sync                       179674       74     0.4   0  Commit
SQL*Net message to client                7        0     0.0   0  Network
DB CPU                                            0           0

I’m also a bit confused as to how the log file sync time can be shorter than the log file write time.

Any assistance or advice would be appreciated.

Regards,

Christopher Osborne

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