Description
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)
> + }
> + } else { // no "to" cache yet...
> + isAssignable = from.isAssignableFrom(to);
> + if (isAssignable)
> + }
> + 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)
> + _typeHash = base.hashCode();
> + _typeCache.put(type, new Integer(_typeHash));
> + } else
> }
> 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
.
> @@ -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?
Attachments
Issue Links
- relates to
-
OPENJPA-138 More performance improvements for OpenJPA (lib and kernel)
-
- Closed
-