On Thu, 31 Oct 2013, John Peterson wrote:
We build a std::map<> from Elem* to a unique sorted contiguous ID, as
Metis only considers the active elements and needs
some contiguous numbering. I expect that gets quite big, and maybe should
be refactored to use a sorted
std::vector<std::pair<Elem*, dof_id_type> > instead?
You are quite correct about this. I ran our memory logger to compare the size of
memory of a map<int,int> and a vector of
pair<int,int>, both with 8M elements. The results were pretty striking:
https://drive.google.com/file/d/0B9BK7pg8se_iaWFzbHlEemxmX0U/edit?usp=sharing
The map's peak memory usage is almost exactly 6X that of the vector's...
Wow, nasty. I was expecting 3X; I forgot about the sizeof(int*) ==
2*sizeof(int) issue.
It's not really relevant here, but out of curiosity, could you give
unordered_map a try?
---
Roy
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