Array/Hash Growth

I'm writing a fairly large scale network app in Perl which is pretty 
dependent on timing.  In the process of optimization, I find myself with 
a lot of questions primarily about array and hash growth.

Is it a big gain to pre-extend the data structures?  With how many 
entries?

Does a newly created array/hash have a default capacity?

Are stacks (arrays, using push and pop) a performance strain because of 
the constant size changes?

Any information along these lines would be greatly appreciated.  Thanks 
for your time.

James

• Array/Hash Growth by James Edward Gray II
• Re: Array/Hash Growth by Ken Williams