[Boost-bugs] [Boost C++ Libraries] #11419: Unexpected memory usage with unorderd_map

Subject: [Boost-bugs] [Boost C++ Libraries] #11419: Unexpected memory usage with unorderd_map
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-06-24 17:28:52

#11419: Unexpected memory usage with unorderd_map
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 Reporter:  DarioOliveri <oliveridario89@…>  |      Owner:  danieljames
     Type:  Bugs                             |     Status:  new
Milestone:  To Be Determined                 |  Component:  unordered
  Version:  Boost Release Branch             |   Severity:  Optimization
 Keywords:                                   |
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 Unordered map does NO rehash when shrinking (erasing specific elements).
 When having multiple maps (or even one map) the memory usage become
 insanely high (arbitrary) and consequently the program lags because of
 insane cache usage

 This is not a memory leak, but a undocumented (and unwanted) behaviour.
 There are 3 possible ( I figured out ) fixes:

 - make rehashing when there are too few elements
 - fix documentation to clearly state users must rehash
 - add a method with the exact purpose of reducing memory usage

 I uploaded the code to reproduce the bug (bug present both in C++11/14 and
 in boost) here:

 *ttps://github.com/Darelbi/PublicProfileTests/blob/master/BoostMemoryUsage/UnorderedMap.cpp

 (beware! running the above code literally freeze also the operative system
 due to huge bandiwth usage).
 Fixing that problem as soon as possible could automatically increase
 performance in a lot of clients code, and that would reduce drastically
 memory usage (wich seems the problem with many applications, it is
 suprising no one profiled that!)

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11419>
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