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Re: st: Addressing > 2 gig of RAM


From   James Muller <james.muller@internode.on.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Addressing > 2 gig of RAM
Date   Mon, 20 Jun 2005 22:31:28 +1000

At the outset, I don't have experience with 64-bit Stata at all, but I can give you some of my _opinions_ on 64-bit computing:

First, you don't need 64 bit if you're going to use no more than 4Gb. 32 bit is 2^32=4Gb. You only actually need 64 bit if you're actually going to need more than 4Gb.

Related, second, are you actually going to need to have >4Gb of data in memory all at the same time? That is a massive amount of data - Stata's most detailed data type is double, which is 8 bytes. That means that you would have to _need_ at some moment in time to be using 2^26=67108864 double objects, which is rare. There is a strong argument then to store your data in a dedicated database, pulling out only the data you need when you need it, and dropping it from memory when it's not needed. And if you did that then Stata is not the best way to go - again, it's worth looking at c or fortran. There are good open source libraries for doing lots of fun things in those languages, and the methods usually aren't too hard to implement oneself anyway. In my opinion worth it for such large apps.

Third, if you're actually doing 64 bit computing then you're after some pretty hardcore efficiency. It is worth at least considering more scientific methods of computing, for example writing custom programs for your application in c or fortran. Like I say, I don't have any experience with 64-bit Stata, but I'd suspect that not too many people would keep using Stata for such large applications.

Fourth, 64-bit computing under Windows is just plain stupid. Sorry for anybody who disagrees, but Windows is an operating system that is inexcusably slow and memory-hungry. Again, 64-bit computing is just that - computing. You're after efficiency so that you're not waiting the next 5 months for the task to end, and you certainly want something stable for time-consuming tasks. Learning to use a proper OS (and using very efficient software in general) is worth it if you're getting into the heavy stuff. Additionally, as is pointed out in a post just before this, Stata needs a contiguous block of memory. Windows does not handle memory well, i.e. you'll not have the whole set of RAM available. A shame after investing in it, not to be able to use it...

Fifth, as far as I'm aware (and I may well have my wires crossed here), current Mac OS's use a variation the Linux kernel, and do so because they are after efficiency and stability. While the hardware of G4/similar is excellent, I'd expect Linux to run better than MacOS on a equivalent hardware.

Sixth, and this definitely depends on the scale of your project, if you're doing stuff that is slow (i.e. trillions and trillions of calculations) then it's worth looking into parallel processing. This, however, steps into the realm of employing a programmer or spending lots of time studying.

Seventh, if you end up going with 64-bit linux, make sure you have an efficient system. 'Linux' has a big reputation as being fast and efficient, but many out-of-the-box distributions pile a bucketload of features that aren't necessary for a lot of situations. They all eat up resources and you end up losing a lot of the advantages. Thus, if you go with something like Fedora Core 64, spend the time giving your system a good haircut - and look carefully at performance reviews and comparisons. Also, ask the guys at Stata about whether their 64-bit Linux Stata will work on the BSDs. BSD is quite nice and should not be dismissed.

Eigth, if you go with 64-bit and choose a PC for your platform, be sure to look into Athlon 64bit CPU.

Overall, my opinion is that if somebody's going to spend the cash to purchase more than 4Gb of RAM and a good 64-bit processor (or processors) then they should spend the time getting their system to do justice to that investment. That means really looking into getting things optimized, which means looking seriously at alternative ways of approaching the problem.

Righto, my sixteen cents there. Hope it's useful.

James




Jon Eckhardt wrote:


Greetings,

I find myself in a situation where I will be able to save a lot of time if
I could address greater than 2 gig of RAM (somewhere around 4 - 6 gig of
RAM would be optimal) in a single stata process. In other words, I would
like to be able to type:

set memory 5g

from within STATA.

It is my understanding from conversations with folks at STATA:

1. This can be achieved with STATA for Windows under a 64bit version of
Windows

2. This can be achieved with STATA for Linux64 (64 bit version of Linux,
such as Red Hat)

3. This can't be achieved with STATA for MAC OSX, due to limitations of the
64bit implementation of MAC Unix. (I have heard that Tiger is fully 64 bit
compatible <http://developer.apple.com/macosx/64bit.html>) but apparently
the official word from STATA corp. is that MAC OSX STATA can't address > 2
gig of RAM.

If you have experience running STATA under any of these configurations
(Windows, Linux, MAC OSX) where you have been able to address > 2 gig of
RAM, I would appreciate your thoughts regarding the true ability to address
large blocks of RAM. Specifically, I'm interested in information regarding
specific configurations that have worked, although I'm interested in other
thoughts you may have regarding this issue as well.

If the MAC works, I would prefer that platform over Linux or Windows.

Thanks in advance,


Jon





Jon Eckhardt, Ph.D.
University of Wisconsin--Madison


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