From: Robert Klemme <shortcutter@...>
Date: 2009-11-10T06:35:26+09:00
Subject: Re: Good or best way to allocate a large array

On 11/09/2009 06:25 PM, Ralph Shnelvar wrote:
> Newbie here:
> 
> I will want/need to create an array of approximately 300K rows and 20
> columns. The array will be an array of either 32-bit quantities or 64-bit quantities.

So we are talking about 300,000 * 20 * 8 ~ 48MB which does not sound too 
large.

robert@fussel:~$ time ruby1.9 -e 'x=1<<63;Array.new(300_000*20) {x}'

real	0m1.922s
user	0m1.288s
sys	0m0.032s
robert@fussel:~$ time ruby1.9 -e 'x=1<<63;Array.new(300_000*20) {1<<63}'

real	0m7.143s
user	0m6.668s
sys	0m0.204s


> Does Ruby support native 64-bit quantities?

Yes.  You can try it out

ruby1.9 -e '100.times {|i| x = 1 << i;p x, x.class}'

> What's a good/best way to to create such an array. Is there a way to
> tell Ruby, "OK, I'm done with this array."

No need to: if there are no more live references to that Array it will 
get collected eventually.

> Can one create such an array such that the garbage collector can
> free the memory in one fast operation?

Probably not because of the number of objects in the Array (if they are 
all Fixnums it will probably a bit faster.

The question is, what do you do with that huge Array?  Chances are that 
you need to allocate more memory during processing.  What's your use 
case?  A database might be an option or a flat file - it all depends.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
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