Re: Service wouldnt start in 8i
- From: Thomas Day <tomday2@xxxxxxxxx>
- To: paul.baumgartel@xxxxxxxxx
- Date: Wed, 30 Nov 2005 15:40:58 -0500
An excellent question that made me go and do some research. The 25%
is a rule-of-thumb that, I believe, came from a Microsoft white paper
circa 1995 related to Windows NT 3.41 and Oracle 7.3. I suspect that
I am guilty of propogating an Oracle myth. A quick search of the
internet came up with the resources below. I can't speak to their
credibilty but they all agree that 25% is way too low.
http://www.orafaq.com/faqwinnt.htm#tuning
"Make sure you have enough memory. If real memory on your system is
limited, the CPU will spend considerable time paging."
http://www.ipass.net/davesisk/oont_performance.htm
"Typically, the best balance on NT is 40-45% of the physical memory
available on the server allocated to the SGA. A rate of memory paging
greater than approximately 5 pages/second will result in exponential
performance degradation. If SGA hit ratios are low, then increase the
memory allocated to the necessary cache. If SGA hit ratios are high
but the O/S is paging more than the suggested minimum, then add more
physical memory to the server. Ideally, the DBA should plan ahead and
budget the purchase of additional memory before hit ratios and paging
becomes a significant bottleneck. If the SGA hit ratios are within the
target range and O/S paging is minimal, then memory is not the
bottleneck. Note that it is possible to allocate too much memory to
the SGA: in this scenario, the SGA hit ratios will be excellent, but
paging will occur at a rate than more than offsets the better hit
ratios, thus making overall performance slower than it would be with
lower SGA hit ratios. The objective for memory should be balancing
between SGA hit ratios and O/S paging."
http://www.dba-oracle.com/oracle_tips_ram_waste.htm
"In my experience the increased data caching can make a huge
difference and for a dedicated Windows server you only need to reserve
20% of the RAM for the OS, and save the rest for SGA and PGA."
http://www.dbazine.com/oracle/or-articles/burleson9
This is another article by Mr. Burleson on computing the optimum SGA size.
http://www.dell.com/downloads/global/solutions/Oracle%20on%20Windows%20Sizing.pdf
A white paper jointly sponsored by Microsoft, Oracle and Dell. It
covers memory requirements and much more.
--
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