Re: 64 bit software

Oradba Linux wrote:

> What are the pros and cons of using 64 bit software ?

It's all about the need for speed ...

On a 64-bit CPU, there can be significant speed advantages when dealing with numbers over 2G. In Oracle this can be very relevant when looking in large SGA (> 2GB) and/or when dealing with large files, and even (in some cases) with large disks.

On a 32-bit CPU, 64-bits can be managed by the operating system and related libraries. Arithmetic operations that _could_ result in numbers > 2G will go through significant hoops by splitting and recombining the numbers. This can have a serious negative performance impact in some situations. Therefore, it is generally not recommended to go 64-bit software on 32-bit hardware for any significant length of time. Indeed, some 32-bit OSs do not support running 64-bit s/w - or at least not until appropriate libraries are added/adjusted.

Therefore, in an Oracle context, if the tablespace datafiles, the SGA and the PGA each can stay less than 2GB, and no (or very few) calculations on the data are larger than 2,147,483,648 (2^(32-1)), performance should be should be good in a completely 32-bit environment.

On the other hand, going 64-bit when the largest number is 2G can be a waste of hardware. (That may not be a significant factor as hardware costs are relatively low.)

Flip side, if any of {files, SGA, PGA, frequent calculations} exceeds 2,000,000,000+some then 64-bit software, on 64-bit hardware, will usually buy significant performance benefits.

Note that the magic 2G limit also applies to raw physical memory when doing direct addressing, and since an Oracle SGA generally uses no more than 1/2 the physical memory, one can legitimately discuss 1GB SGA in the above context.

... and keeping it around for a while, as in "how do you record time?"

According to the *nix family (and others), the universe started with a big bang on Jan 1, 1972. For the 32-bit members of this family the universe, as we know it, will end on January 19, 2038 (see http://www.deepsky.com/~merovech/2038.html)

AFAIK, this one does not affect Oracle directly. (Then again, if the underlying system keels over, I guess you could say it affects Oracle.) Can you say "Y2K v2"?

/Hans Received on Thu Sep 02 2004 - 00:03:17 CDT