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Tuning Oracle redo logs

Oracle Tips by Burleson Consulting

 

Question: What is the best way to tune the Oracle redo logs?

 

Answer: Oracle redo logs are archived when you turn-on archivelog mode, and the overhead relates to the work done by the LGWR and ARCH background processes as they write the redo information. 

 

The steps for tuning redo log performance are straightforward:

 

1 - Determine the optimal sizing of the log_buffer.
 

2 - Size online redo logs to control the frequency of log switches and minimize system waits.


3 - Optimize the redo log disk to prevent bottlenecks.  In high-update databases, no amount of disk tuning may relieve redo log bottlenecks, because Oracle must push all updates, for all disks, into a single redo location.

 

 

Once you have optimized your redo and I/O sub-system, you have few options to relieve redo-induced contention.  This can be overcome by employing super-fast solid-state disk for your online redo log files, since SSD has far greater bandwidth than platter disk.  This will greatly improve DML throughput for high-update databases.  As SSD prices continue to fall, SSD becomes increasing affordable, and SSD will someday replace spindle platter disk for all Oracle data storage.

 

For more details on redo log tuning, see these books:

 

Also see these related notes on redo log tuning:

Market Survey of SSD vendors for Oracle:

There are many vendors who offer rack-mount solid-state disk that work with Oracle databases, and the competitive market ensures that product offerings will continuously improve while prices fall.  SearchStorage notes that SSD is will soon replace platter disks and that hundreds of SSD vendors may enter the market:

"The number of vendors in this category could rise to several hundred in the next 3 years as enterprise users become more familiar with the benefits of this type of storage."

As of January 2013, many of the major hardware vendors (including Sun and EMC) are replacing slow disks with RAM-based disks, and Sun announced that all of their large servers will offer SSD.

Here are the major SSD vendors for Oracle databases (vendors are listed alphabetically):

2008 rack mount SSD Performance Statistics

SearchStorage has done a comprehensive survey of rack mount SSD vendors, and lists these SSD rack mount vendors, with this showing the fastest rack-mount SSD devices:

manufacturer model technology interface performance metrics and notes
IBM RamSan-400 RAM SSD

Fibre Channel
InfiniBand

3,000MB/s random sustained external throughput, 400,000 random IOPS
Violin Memory Violin 1010 RAM SSD

PCIe

1,400MB/s read, 1,00MB/s write with ×4 PCIe, 3 microseconds latency
Solid Access Technologies USSD 200FC RAM SSD

Fibre Channel
SAS
SCSI

391MB/s random sustained read or write per port (full duplex is 719MB/s), with 8 x 4Gbps FC ports aggregated throughput is approx 2,000MB/s, 320,000 IOPS
Curtis HyperXCLR R1000 RAM SSD

Fibre Channel

197MB/s sustained R/W transfer rate, 35,000 IOPS

Choosing the right SSD for Oracle

When evaluating SSD for Oracle databases you need to consider performance (throughput and response time), reliability (Mean Time Between failures) and TCO (total cost of ownership).  Most SSD vendors will provide a test RAM disk array for benchmark testing so that you can choose the vendor who offers the best price/performance ratio.

Burleson Consulting does not partner with any SSD vendors and we provide independent advice in this constantly-changing market.  BC was one of the earliest adopters of SSD for Oracle and we have been deploying SSD on Oracle database since 2005 and we have experienced SSD experts to help any Oracle shop evaluate whether SSD is right for your application.  BC experts can also help you choose the SSD that is best for your database.  Just  call 800-766-1884 or e-mail.:  for SSD support details.

DRAM SSD vs. Flash SSD

With all the talk about the Oracle “flash cache”, it is important to note that there are two types of SSD, and only DRAM SSD is suitable for Oracle database storage.  The flash type SSD suffers from serious shortcomings, namely a degradation of access speed over time.  At first, Flash SSD is 5 times faster than a platter disk, but after some usage the average read time becomes far slower than a hard drive.  For Oracle, only rack-mounted DRAM SSD is acceptable for good performance:

Avg. Read speed

Avg. write speed

Platter disk

10.0 ms.

  7.0 ms.

DRAM SSD

 0.4 ms.

  0.4 ms.

Flash SSD    

 1.7 ms.

 94.5 ms.

 

 
If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


 

 

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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  and include the URL for the page.


                    









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