Re: performance of map in MSVC 10b2
Jim Z. Shi wrote:
I use map a lot in my daily work, so the performance of map is very
important to me. today i did a very simple test on MSVC10b2,
I believe MSVC9 didn't turn off iterator debugging unless you specifically
told it to, not even when compiling for release. This might make a big
difference if they still do it. For Boost, you have to explicitly turn it
on instead.
for(int i=0; i<size; ++i) {
imap[i] = "test";
++prog_bar;
}
Maps are trees, sorted by the key. Since your key increases monotonically,
every time you insert an element that insert takes place at the same branch
of the tree, so it becomes unbalanced. This doesn't help performance at
all. Suggestion: Unless this really represents your use case, I would
create a vector first, fill it like above and then shuffle the elements,
before using them as keys to insert.
I don't know enough about how the unordered_maps are implemented to make an
educated guess about their behaviour.
for(int i=0; i<size; ++i) {
buff = imap[i];
}
This test is fine, unless of course the map stays unbalanced somehow, which
would mess up the lookup time. I don't think this happens though.
MAP INSERT FIND
std::map 7.73s 1.98s
boost::unorder_map 5.47s 0.80s
std::unorder_map 9.91s 2.98s
Interesting, thanks for these numbers!
Uli
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