Re: [Boost-users] Default table size of unordered map

2009/7/1 Dominique Devienne :

On Tue, Jun 30, 2009 at 9:18 PM, MeMooMeM wrote:

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What is the default table size of unordered maps in boost? I am trying to figure out how scalable this function is. My guess is that boost assumes a default initial table length. If it is exceeded, it needs to re-create hashes for all entries to grow it, which is costly. I would like to find that threshold...

Thanks so much!

See http://www.boost.org/doc/libs/1_39_0/doc/html/unordered/buckets.html#unorder...

That part of the documentation should also mention that you can also give a minimum number of buckets in the constructor. So if you want to start with a least 10000 buckets: boost::unordered_map m(10000); Also, if you're concerned about scalability, don't use boost 1.38, there's a bug in it which causes performance to degrade for large numbers of buckets. Daniel