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From "Craig Russell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-141) More performance improvements (in response to changes for OPENJPA-138)
Date Thu, 15 Feb 2007 01:55:05 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473285
] 

Craig Russell commented on OPENJPA-141:
---------------------------------------

>> If we want a "hard cache that drops entries for classes that are redeployed", then

>> we should be using weak keys and hard values. If we want a "memory sensitive" 
>> cache, then we should be using hard keys and soft values. 

>I vaguely prefer a "hard cache that drops entries for classes that are redeployed", since
I care more about speed than memory footprint.

This is also affected by whether we use a giant cache (including all the EMFs) or one cache
per EMF. I prefer one cache per EMF because it simplifies the cache entry life cycle. During
EMF close, the cache can be explicitly cleared, which allows the garbage collector to be more
efficient since it doesn't have to scan all the entries in the cache. 

> More performance improvements (in response to changes for OPENJPA-138)
> ----------------------------------------------------------------------
>
>                 Key: OPENJPA-141
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-141
>             Project: OpenJPA
>          Issue Type: Sub-task
>          Components: jpa
>            Reporter: Kevin Sutter
>         Assigned To: Kevin Sutter
>         Attachments: openjpa-141.txt
>
>
> Abe's response to my committed changes for OPENJPA-138.  I will be working with Abe and
my performance team to work through these issues...
> > ======================================================================
> > ========
> > --- incubator/openjpa/trunk/openjpa-kernel/src/main/java/org/apache/
> > openjpa/ee/JNDIManagedRuntime.java (original)
> > +++ incubator/openjpa/trunk/openjpa-kernel/src/main/java/org/apache/
> > openjpa/ee/JNDIManagedRuntime.java Sun Feb 11 18:33:05 2007
> > @@ -29,6 +29,7 @@
> >      implements ManagedRuntime {
> >
> >      private String _tmLoc = "java:/TransactionManager";
> > +    private static TransactionManager _tm;
> Whoa, I didn't think you meant caching the TM statically.  That has
> to be backed out.  You can cache it in an instance variable, but not
> statically.  Nothing should prevent someone having two different
> BrokerFactories accessing two different TMs at two different JNDI
> locations.
> BrokerImpl:
> > +     * Cache from/to assignments to avoid Class.isAssignableFrom
> > overhead
> > +     * @param from the target Class
> > +     * @param to the Class to test
> > +     * @return true if the "to" class could be assigned to "from"
> > class
> > +     */
> > +    private boolean isAssignable(Class from, Class to) {
> > +      boolean isAssignable;
> > +      ConcurrentReferenceHashMap assignableTo =
> > +          (ConcurrentReferenceHashMap) _assignableTypes.get(from);
> > +
> > +      if (assignableTo != null) { // "to" cache exists...
> > +          isAssignable = (assignableTo.get(to) != null);
> > +          if (!isAssignable) { // not in the map yet...
> > +              isAssignable = from.isAssignableFrom(to);
> > +              if (isAssignable) {
> > +                  assignableTo.put(to, new Object());
> > +              }
> > +          }
> > +      } else { // no "to" cache yet...
> > +          isAssignable = from.isAssignableFrom(to);
> > +          if (isAssignable) {
> > +              assignableTo = new ConcurrentReferenceHashMap(
> > +                      ReferenceMap.HARD, ReferenceMap.WEAK);
> > +              _assignableTypes.put(from, assignableTo);
> > +              assignableTo.put(to, new Object());
> > +          }
> > +      }
> > +      return isAssignable;
> > +    }
> This code could be simplified a lot.  Also, I don't understand what
> you're trying to do from a memory management perspective.  For the
> _assignableTypes member you've got the Class keys using hard refs and
> the Map values using weak refs.  No outside code references the Map
> values, so all entries should be eligible for GC pretty much
> immediately.  The way reference hash maps work prevents them from
> expunging stale entries except on mutators, but still... every time a
> new entry is added, all the old entries should be getting GC'd and
> removed.  Same for the individual Map values, which again map a hard
> class ref to an unreferenced object value with a weak ref.  Basically
> the whole map-of-maps system should never contain more than one entry
> total after a GC run and a mutation.
> I'd really like to see you run your tests under a different JVM,
> because it seems to me like (a) this shouldn't be necessary in the
> first place, and (b) if this is working, it's again only because of
> some JVM particulars or GC timing particulars or testing particulars
> (I've seen profilers skew results in random ways like this) or even a
> bug in ConcurrentReferenceHashMap.
> The same goes for all the repeat logic in FetchConfigurationImpl.
> And if we keep this code or some variant of it, I strongly suggest
> moving it to a common place like ImplHelper.
> > +    /**
> > +     * Generate the hashcode for this Id.  Cache the type's
> > generated hashcode
> > +     * so that it doesn't have to be generated each time.
> > +     */
> >      public int hashCode() {
> >          if (_typeHash == 0) {
> > -            Class base = type;
> > -            while (base.getSuperclass() != null
> > -                && base.getSuperclass() != Object.class)
> > -                base = base.getSuperclass();
> > -            _typeHash = base.hashCode();
> > +            Integer typeHashInt = (Integer) _typeCache.get(type);
> > +            if (typeHashInt == null) {
> > +                Class base = type;
> > +                Class superclass = base.getSuperclass();
> > +                while (superclass != null && superclass !=
> > Object.class) {
> > +                    base = base.getSuperclass();
> > +                    superclass = base.getSuperclass();
> > +                }
> > +                _typeHash = base.hashCode();
> > +                _typeCache.put(type, new Integer(_typeHash));
> > +            } else {
> > +                _typeHash = typeHashInt.intValue();
> > +            }
> >          }
> >          return _typeHash ^ idHash();
> >      }
> Once again, you're mapping a hard Class ref to a value with no
> outside references held in a weak ref.  Once again that means the
> entry should be immediately eligible for GC, and therefore should be
> removed on the next mutation of the cache, subject to GC timing.  And
> again I'd like to know what your JVM is doing to make Class.hashCode
> take an appreciable amount of time.  Aren't Class instances supposed
> to be singletons?  What if we just used System.identityHashCode(cls)?
> > Modified: incubator/openjpa/trunk/openjpa-lib/src/main/java/org/
> > apache/openjpa/lib/conf/ObjectValue.java
> > URL: http://svn.apache.org/viewvc/incubator/openjpa/trunk/openjpa-
> > lib/src/main/java/org/apache/openjpa/lib/conf/ObjectValue.java?
> > view=diff&rev=506230&r1=506229&r2=506230
> > ======================================================================
> > ========
> > --- incubator/openjpa/trunk/openjpa-lib/src/main/java/org/apache/
> > openjpa/lib/conf/ObjectValue.java (original)
> > +++ incubator/openjpa/trunk/openjpa-lib/src/main/java/org/apache/
> > openjpa/lib/conf/ObjectValue.java Sun Feb 11 18:33:05 2007
> > @@ -17,6 +17,8 @@
> >
> >  import org.apache.commons.lang.ObjectUtils;
> >  import org.apache.openjpa.lib.util.Localizer;
> > +import org.apache.openjpa.lib.util.ReferenceMap;
> > +import
> > org.apache.openjpa.lib.util.concurrent.ConcurrentReferenceHashMap;
> >
> >  /**
> >   * An object {@link Value}.
> > @@ -28,6 +30,10 @@
> >      private static final Localizer _loc = Localizer.forPackage
> >          (ObjectValue.class);
> >
> > +    // cache the types' classloader
> > +    private static ConcurrentReferenceHashMap _classloaderCache =
> > +        new ConcurrentReferenceHashMap(ReferenceMap.HARD,
> > ReferenceMap.WEAK);
> This maps a hard Class ref to a weak ClassLoader ref.  Given that a
> Class references its ClassLoader (or is supposed to -- again I wonder
> what the hell the JVM you're using is doing where
> Class.getClassLoader is taking a long time), no entries will ever
> expire from this map.
> Have you tried running your benchmarks without all the caching of
> assignables and classloaders and hashcodes (all Class methods, btw)
> and just the other improvements?  Or with any other JVM?

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