Re: Excessive memory usage of large hash_maps

[pcarlini at unitus dot it]

Quoting Paul Dubuc <pdubuc@cas.org>: 
 
> Hash containers are apparently resized on based on a table of prime numbers 
>  
> (__stl_prime_list) in stl_hashtable.h.  As a hash table grows space (number 
> of  
> buckets) is reallocated based on the next higher number in this list.  The  
> numbers roughly double with each increment.  This isn't noticable in the 
> lower  
> increments, but can result in a lot of wasted space in the larger ones.  Why 
>  
> should the size continue to double once we get above, say 98317?  Couldn't  
> smaller increments be inserted here to conserve memory?  Better yet provide 
a 
>  
> nice way to override the __stl_next_prime() function? 
 
Hi Paul. Thanks for your suggestion. 
 
FYI, we are in the process (at least I am ;) of adapting the current 
__gnu_cxx::hash* code to provide an experimental implementation of Matt 
Austern standard proposal for hashed containers, as described in the Library 
Technical Report, see: 
 
	http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1456.html 
 
Please have a look, this is our reference for the project. I hope to provide a 
detailed roadmap in a couple of weeks. 
 
Paolo.