Default table size of unordered map
Hi, 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! -- View this message in context: http://www.nabble.com/Default-table-size-of-unordered-map-tp24283133p2428313... Sent from the Boost - Users mailing list archive at Nabble.com.
On Tue, Jun 30, 2009 at 9:18 PM, MeMooMeM<mbelgin@gmail.com> wrote:
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... --DD
2009/7/1 Dominique Devienne <ddevienne@gmail.com>:
On Tue, Jun 30, 2009 at 9:18 PM, MeMooMeM<mbelgin@gmail.com> wrote:
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<int, int> 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
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MeMooMeM