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Re: st: Addressing > 2 gig of RAM


From   "Michael Blasnik" <michael.blasnik@verizon.net>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Addressing > 2 gig of RAM
Date   Mon, 20 Jun 2005 10:45:31 -0400

It sounds like you don't have any real experience in working with large datasets (in Stata or otherwise) and have no actual measured results of different computing platforms in terms of speed, but instead want to promote some agenda. It may be "rare" for you to work with very large datasets, but some people do it on a regular basis, especially those that work with large scale admistrative databases (e.g., national health programs or, in my case, utility company databases which I admit only tend to run up to about 1GB).

You are incorrect that you only need 64bit computing if you are going to use more 4GB of data-- do you know of a 32bit OS/hardware platform that can allocate 4GB of ram to a process? or even 3GB? There have been Statalist postings showing about 2GB data area max for Mac OS 10.3 on a G5 and other posts indicating that about 2GB will be the max for most 32bit OSs. Maybe 32bit Linux can allocate more, but I haven't heard that. 64bit also provides potential speed improvements, not just max RAM allocation (see below).

I don't think it makes much sense to start writing your own data analysis system in C if you already have a developed and tested tool (like Stata) that does what you want. It is far easier (and cheaper by an order of magnitude or more) to buy a 64bit platform, load it with RAM and use Stata than it is to write your own code from scratch, especially if you want to do many things. Perhaps if you have one big repeating analysis it may make sense to write some code, but Stata is actually quite fast even with very large datasets, especially if you know what you're doing to optimize your Stata code.

While Windows has many shortcomings, your comment that 64bit computing under Windows is "stupid" does not appear to be backed up by any actual tests or comparisons. You say that Windows is "inexcusably slow" but all of the comparisons I've seen posted to Statalist and elsewhere seem to indicate that, for massive data analysis, the speed of execution is comparable across equal-bit operating systems. Comparisons of GAUSS speed on different platforms/OSs at

http://www.scientificweb.com/testreport/gaussbench2.html

doesn't seem to show Windows lagging Linux, results are mixed across tests. I'd be interested in seeing any actual data you have showing Win64 being substantially slower at computational tasks than another OS since I am considering moving to 64bit soon.

There was a Statalist posting that showed moving from 32bit WinXP to 64bit Linux (both with AMD 64bit processors, but different models) led to 29%-34% speed improvements in calculating some complex gllamm models. But this difference is between 32bit and 64bit. see:

http://www.stata.com/statalist/archive/2004-04/msg00620.html

Michael Blasnik
michael.blasnik@verizon.net


----- Original Message ----- From: "James Muller" <james.muller@internode.on.net>
To: <statalist@hsphsun2.harvard.edu>
Sent: Monday, June 20, 2005 8:31 AM
Subject: Re: st: Addressing > 2 gig of RAM



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
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