CF Performance vs. Foundation (Re: Worth it for an object to cache its own IMPs?)

[glen.low at pixelglow.com (Glen Low)]

On 02/03/2004, at 6:46 AM, Scott Stevenson wrote:

>
> On Mar 1, 2004, at 2:18 AM, Izidor Jerebic wrote:
>
>> What do you mean by parsing? Reading from a file and building a tree 
>> structure or walking the structure already built? Extracting parts of 
>> files or reading complete files as trees of objects for later 
>> perusal?
>
> Basically, I have hierarchy of arrays and dictionaries that are all 
> loaded into memory at startup. As the program runs, I need to get at 
> various parts of the structures very frequently. Right now, it's just 
> too slow.

I've found that the CF objects can be more flexible than their NS 
equivalents. For example, instead of doing key1 -> object, key2 -> 
object in NSDictionary, you can just do two different kinds of CFSet 
with different callbacks -> should be faster, easier to do 
cross-lookups and less objects in memory. The other advantage is that 
the key object doesn't really need to be an object in a CFDictionary, 
so you might get some optimization that way if the equal: and/or hash: 
calls are too prevalent or inefficient.

One thing I learnt from STL experience is often a dictionary is more 
inefficient than a set, especially if the value object needs to know 
its key.

The other thing to think about is whether you can flatten your 
hierarchy somewhat. Instead of key1 -> (key2 -> object), try something 
like (key1, key2) -> object. The multiple objects for a single key 
collections will help e.g. bags.

[preaching mode on]

You said you're at the optimization stage and would prefer not to 
change your data structures. But often it is changing the algorithm 
that will deliver the significantly faster result, rather than tweaking 
the low-level details. Premature optimization may be root of all evil, 
but sometimes the optimization required is a change of data structure 
and/or algorithm. Consider yourself at a local maximum in your graph, 
you still have to search for the global maximum rather than get stuck 
in the same spot.

[preaching mode off]

Cheers, Glen Low


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