[Hibernate-issues] [Hibernate-JIRA] Created: (HHH-1789) HashMap initialization is very unefficient in cache hits

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HashMap initialization is very unefficient in cache hits
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         Key: HHH-1789
         URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH=
-1789
     Project: Hibernate3
        Type: Improvement

 Environment: hibernate 3, db n/a
    Reporter: Aapo Kyr=C3=B6l=C3=A4


We have an entity which has a <map>-type of collection attached to it, that=
 uses <many-to-many> mapping. The map has cache setting of <cache usage=3D"=
nonstrict-read-write"/>=20

The problem is that the map is often quite large, 500-1000 elements in it. =
But when Hibernate3 instantiates it from cache (PersistentMap.initializeFro=
mCache()), it will create a HashMap with default parameters and then .put()=
 each item from the serialized cache data to the map.=20

HashMap default size is 16 and it resizes it to double always when it has 7=
5%*capacity elements in it. So, initializing a HashMap with 1000 entries wi=
ll cause 7 resizes (which are expensive): 16->32->64->128->256->512->1024->=
2048. This consumes a lot of memory and cpu because HashMap.resize() is a c=
ostly operation.=20

It would be better for Hibernate to initialize the map with loadfactor 1.0 =
and size of the cached serialized data array / 2 + some extra.=20



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