maximum size & TCP::collect

As a rule of thumb, what is the maximum amount of memory available to an iRule? For example, if I'm implementing an ACL or blacklist, what's the maximum number of entries I should have in an array?

 

 

I noticed the DNS Flood iRule in the DevShare section has two arrays, but no bounds checking to limit memory consumption.

 

 

Also, what does TCP::collect do when called without an argument? Does it obtain all currently available bytes into TCP::payload?