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To help us decide whether to install a 32bit or 64bit flavour of Oracle, I need to find out the advantages and disadvantages of the two choices. Yes, I do know that the 32bit option restricts us to less than 4GB per process. Yes, I do know that utilizing more than 4GB on a 32bit OS is tricky, but that part is handled by the OS very well these days (being it Linux or Windows).

My question is more on the topic: Will the memory demand of a 64bit OS (including the 64bit flavour of Oracle) require more physical memory than the 32bit counterpart does? And if so, how much overhead will there be? Reason for asking is that we do not have unlimited physical memory available.

Does it make a difference if we use a 32bit version under Linux or Windows (I assume under 64bit it does not)? My gut feel is that Oracle on windows is not as good as on Linux in handling memory sizes > 4gb in its 32bit flavour. Am I right?

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What is the lifetime of your database ? Anything expecting to last more than a year or so, and I wouldn't even think about 32-bit. Even if it is short-lived, I'd only consider 32-bit for a very small app (eg one I might run on a very cheap hosting/cloud environment).

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Agreed, but even in a VM I would choose 64 bit for Oracle. –  Antonius Bloch Jan 25 '11 at 1:17
    
What role does the expected lifetime of the database play in finding the decision? If 32bit works well for half a year, why shouldn't it be appropriate for a longer lifetime? The usage of the database will not change over time. My fear is that a 64bit version requires more RAM and the available memory on the machine is restricted. –  struppi Jan 25 '11 at 7:45
    
Because I wouldn't expect to be running 32-bit OS's in the medium/long term. Frankly, if you've got a 64-bit chip, I'd use a 64-bit OS and 64-bit app software. –  Gary Jan 27 '11 at 22:08
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64 bit will use slightly more RAM, but memory is cheap. 64 bit will really outperform 32 bit. The model used for extended memory access under a 32 bit OS entails a substantial performance penalty. It's definitely not worth the slightly advantageous memory usage.

Plus Oracle LOVES memory. So you will have a problem scaling if you choose 32 bit. Don't do it.

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Do you have experience in what "slightly more" means? Is it 5 percent more, 10? 30? We have 16 Gig available, not more. –  struppi Jan 25 '11 at 7:51
    
You have 16GB available for 1 database? or multiple databases? –  Todd Pierce Jan 26 '11 at 18:02
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