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From "Hernan Otero (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AVRO-946) GenericData.resolveUnion() performance improvement
Date Mon, 31 Oct 2011 13:17:32 GMT

    [ https://issues.apache.org/jira/browse/AVRO-946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13140133#comment-13140133
] 

Hernan Otero commented on AVRO-946:
-----------------------------------

Thanks for the feed back.

Yes, I think your proposed solution would also solve the performance issue.

The only question I'd have is regarding adding the Union as one of the keys in the MultiKeyMap
(in GenericDatumWriter).  Unless we force identity equality (something we can't rely on within
our project), there's nothing else we could use within the Union as an alternative that would
still make it unique within the entire schema, is there? (this is only a problem for the Union,
for the other key, the datum's schema, we could use getFullName() as an alternative).

Or am I missing something?

Thanks!

Hernan
                
> GenericData.resolveUnion() performance improvement
> --------------------------------------------------
>
>                 Key: AVRO-946
>                 URL: https://issues.apache.org/jira/browse/AVRO-946
>             Project: Avro
>          Issue Type: Improvement
>          Components: java
>    Affects Versions: 1.6.0
>            Reporter: Hernan Otero
>
> Due to the sequential nature of today's implementation of GenericData.resolveUnion()
(used when serializing an object):
> {code}
>   public int resolveUnion(Schema union, Object datum) {
>     int i = 0;
>     for (Schema type : union.getTypes()) {
>       if (instanceOf(type, datum))
>         return i;
>       i++;
>     }
>     throw new UnresolvedUnionException(union, datum);
>   }
> {code}
> it showed up when we were doing some serialization performance analysis.  A simple optimization
can be implemented by keeping a map within the UnionSchema object (in fact, this could actually
be a perfect hash map given the potential values in the map are known in advance).  The optimization
is obviously most notable when a Union within the schema contains many types (in our particular
use case, more than 40 in some cases).  In this scenario, we observed a 25% improvement by
using an identity hash map.
> Even though using an identity map provides a significant boost, we have observed an even
further improvement (and removed some of the restrictions of relying on object identity) by
using a perfect hash map on the schema names (an extra 15% on top of that in some cases).
 This implementation, unfortunately, is not something we could contribute at this point, but
we thought it'd be a good idea to allow users to provide alternative implementations of the
indexing behavior, such as adding the following static method to Schema:
> {code}
> public static void setUnionTypeIndexCacheFactory(UnionIndexCacheFactory factory)
> {
>   unionIndexCacheFactory = factory;
> }
> {code}
> This is what the interface and identity hash map-based implementation would look like:
> {code}
>   /**
>    * A factory interface for creating UnionTypeIndexCache instances.
>    */
>   public static interface UnionIndexCacheFactory
>   {
>       UnionIndexCache createUnionIndexCache(List<Schema> types);
>       /**
>        * Used for caching schema indices within a union.
>        */
>       public static interface UnionIndexCache
>       {
>           void setTypeIndex(Schema schema, int index);
>           int getTypeIndex(Schema schema);
>       }
>   }
>   private static class IdentityMapUnionIndexCacheFactory implements UnionIndexCacheFactory
>   {
>       @Override
>       public UnionIndexCache createUnionIndexCache(List<Schema> types)
>       {
>           return new UnionIndexCache()
>           {
>               private final IdentityHashMap<Schema, Integer> schemaToIndex = new
IdentityHashMap<Schema, Integer>();
>               @Override
>               public void setTypeIndex(Schema schema, int index)
>               {
>                   schemaToIndex.put(schema, index);
>               }
>               @Override
>               public int getTypeIndex(Schema schema)
>               {
>                   Integer index = schemaToIndex.get(schema);
>                   return index == null ? -1 : index;
>               }
>           };
>       }
>   }
> {code}
> I will attach a patch later today or early tomorrow.
> Thanks in advance,
> Hernan Otero

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