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>
  • Date: Sat, 12 Jan 2008 00:29:32 -0700


<<< Qs How should this issue be approached? >>>
1. Presuming an OLTP system, you would be committing when the transaction is
done. Nevertheless you should verify that you are committing in a manner
that models the business transaction and not based on a, perhaps, contrived

2. You are trying to deal with the aggregate with this report. What part of
the response time is the log file sync (commit) time? Take one of the
threads of this benchmark and run a level 8 SQL trace to get a more accurate
picture of its influence.

3. I would look at whether you are IO bound or so CPU bound that the LGWR is
not getting time. And determine the time log writer to is made to write vs
its default timer and thresholds.

Cary Millsap's work in
Steve Adams' work in

Krish Hariharan
President/Executive Architect, Quasar Database Technologies, LLC


-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
Sent: Friday, January 11, 2008 6:57 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: High "log file sync" Waits in Statspack, - Online Redo Logs on
Mounted File system of SAN Storage


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

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


Top 5 Timed Events                                                 Avg

~~~~~~~~~~~~~~~~~~                                                 wait

Event                                     Waits        Time (s)    (ms)

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

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

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

CPU time 31,699 7.1

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

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

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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