RE: High "log file sync" Waits in Statspack, - Online Redo Logs on Mounted File system of SAN Storage

  • From: <krish.hariharan@xxxxxxxxxxxx>
  • To: <VIVEK_SHARMA@xxxxxxxxxxx>, <richa03@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Sat, 12 Jan 2008 02:42:41 -0700

Vivek,

Multi block read count: Since, this is an OLTP work load, as a
generalization, you should not be affected by it significantly. If you are
being affected, you should look at the SQL.

ASYNC IO: I don't prefer the simulation of kaio with threaded io for file
systems. Are you running file systems or ASM? If not, you should consider
ASM for its benefits. I prefer to run my systems on file systems with direct
io and ASM with async io. I wonder if this is causing the %sys to be
inflated.

In Solaris 10 WIO is reported as Idle so you could be IO bound, you have to
look at sql traces and iostat

Regards,
-Krish
Krish Hariharan
President/Executive Architect, Quasar Database Technologies, LLC
http://www.linkedin.com/in/quasardb

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of VIVEK_SHARMA
Sent: Saturday, January 12, 2008 1:40 AM
To: richa03@xxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: RE: High "log file sync" Waits in Statspack, - Online Redo Logs on
Mounted File system of SAN Storage


Thanks Richa, folks for the support & related Link(Kevin Closson's)



% System CPU usage is about DOUBLE of %User CPU usage:-

Qs What could be the possible cause?

NOTE - db_file_multi_block_read_count was NOT set by Oversight & defaulted
to a value of 98. Could this be a probable cause?



Qs Should LGWR process be set to a Higher CPU priority(using renice) since
60% of the CPU power is FREE/Unused?
NOTE - cpu_count=80

Solaris 10



From Statspack  - NON-RAC setup (Oracle 10.2.0.3):-

Host CPU (CPUs: 80)

~~~~~~~~ Load Average

Begin    End      User    System   Idle   WIO     WCPU

------- -------   ------- ------- ------- ------- --------

                9.13    1.79

               16.35   23.30   60.35    0.00    2.79



Additional replies to your questions, are given below prefixed by "=>"



Cheers

________________________________________
From: richa03@xxxxxxxxx [richa03@xxxxxxxxx]
Sent: Saturday, January 12, 2008 8:11 AM
To: VIVEK_SHARMA
Subject: Re: High "log file sync" Waits in Statspack, - Online Redo Logs on
Mounted File system of SAN Storage

Are you using asyncIO for DBWR?

disk_async_io=TRUE (Default)

How many sessions were active during the run?

10,000

How long was the run in wallclock time?

45 minutes

What is the priority of the Oracle processes?

=> Default [Higher priority (using renice) NOT set yet.]

________________________________________

Folks

During a Benchmark Run of OLTP Transactions very High "log file sync" wait
is occuring
Storage Box - Sun StoreEdge 9990V (Hitachi SAN)
Online Redo logfiles exist on Mounted Filesystem on a LUN / Volume of 4+4
Hard Disks , (RAID 1+0 Type)
Hard Disk - 15 K RPM
Storage Cache - 128 GB
Online Redo Logfile size 750 MB
log_buffer= 4M

Oracle 10.2.0.3
Solaris 10

Qs On the Storage Box, should a few of its HBA Controllers & respective
Ports be assigned dedicatedly only to the online Redo LUN / Volume?
Qs Should Online Redo Logiles be moved to RAW Devices on the SAN Storage?
Qs Any advisable init.ora parameters?

Qs How should this issue be approached?

Will share Statspack as needed

Cheers & Thanks

P.S.

Top 5 Timed Events                                                 Avg
%Total

~~~~~~~~~~~~~~~~~~                                                 wait
Call

Event                                     Waits        Time (s)    (ms)
Time

----------------------------------------- ------------ ----------- ------
------

log file sync                             3,511,274    328,288     93
73.6

SQL*Net break/reset to client             732,491      49,120      67
11.0

CPU time 31,699 7.1

latch: virtual circuit queues             1,099,453    10,695      10
2.4

db file parallel write                    3,253,478    9,535       3
2.1

-------------------------------------------------------------



Host CPU (CPUs: 80)

~~~~~~~~ Load Average

Begin    End      User    System   Idle   WIO     WCPU

------- -------   ------- ------- ------- ------- --------

                9.13    1.79

               16.35   23.30   60.35    0.00    2.79



Load Profile     Per Second Per  Transaction

~~~~~~~~~~~~     --------------- ---------------

Redo size:       3,143,457.88    4,121.10

...

Block changes:   15,320.88       20.09

...

Physical writes: 2,176.56        2.85

User calls:      14,769.89       19.36

...

Logons:          3.55            0.00

Executes:        12,950.32       16.98

Transactions:    762.77

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