From: Matthew Smillie <M.B.Smillie@...>
Date: 2005-11-09T19:04:49+09:00
Subject: Re: Question about symbols

On Nov 9, 2005, at 8:32, Robert Klemme wrote:

>> Symbols are never garbage-collected, so you should not use them for
>> situations where you could have an unbounded number of unique
>> symbol values.
>
> That's why I recommended to use them with a limited set of values  
> only.
>
> Hope that makes things a bit clearer.

I wonder if I could trouble the list a bit further on this one: I've  
got a collection of newswire articles, and I was thinking of using  
symbols to represent the words in each.  I'd likely only ever be  
using a half-dozen articles at any one time, but I'd be using on the  
order of tens of thousands of articles over the course of the  
program.  My hunch is that to avoid stuffing memory full of unused  
symbols, I should deal with each subset of articles in a forked  
process - I'm assuming that since threads run in the interpreter,  
they'll share the same symbol ids as the parent.

This raises a couple of quick questions: firstly, how big is a  
"limited set", in a hand-waving, give or take an order-of-magnitude  
sort of estimate?

Secondly, I note that the FAQ says that fork "is slow".  Am I right  
to think that's simply the overhead of starting up the thread, and  
then things run smoothly thereafter, or is there some other penalty  
of which I'm not aware?

thanks in advance & all enlightenment appreciated.

matthew smillie.