Re: Service wouldnt start in 8i

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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