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https://issues.apache.org/jira/browse/GORA-401?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14250112#comment-14250112
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Renato Javier Marroquín Mogrovejo commented on GORA-401:
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Hi guys,
So I think [~lewismc] actually explained pretty well on the mailing list. These
files were used when we were using our old data beans compiler and not Avro's.
For serializing the internal fields of the entities, what do you mean? the
__g__dirty? that is just an in-memory data structure to verify that the entity
hasn't changed while we had it. Also Ed did this when he re-worked the Avro
compiler.
For the example of using the object from Map to Reduce, this doesn't assure
that the Reducer will be on the same machine as the Mapper. This means that
they may not share memory which in turn means that you need to read the entity
from disk again and that should be not dirty (you are just first reading it, no
changes yet). Dirty state is just an in-memory per-process. So what would
happen if you have two mappers reading the same entity in different machines
and modifying the entity differently. how would you determine on the reducer
which one is the correct one?
Probably Nutch problem is something else, I will try to look into it.
> Serialization and deserialization of Persistent does not hold the entity
> dirty state
> ------------------------------------------------------------------------------------
>
> Key: GORA-401
> URL: https://issues.apache.org/jira/browse/GORA-401
> Project: Apache Gora
> Issue Type: Bug
> Components: gora-core
> Affects Versions: 0.4, 0.5
> Environment: Tested on gora-0.4, but seems logically to hold on
> gora-0.5
> Reporter: Alfonso Nishikawa
> Priority: Critical
> Labels: serialization
> Original Estimate: 35h
> Remaining Estimate: 35h
>
> After removing __g__dirty field in GORA-326, dirty field is not serialized.
> In GORA-321
> {{[PersistentSerializer|https://github.com/apache/gora/blob/master/gora-core/src/main/java/org/apache/gora/mapreduce/PersistentSerializer.java]}}
> went from using
> {{[PersistentDatumWriter|https://github.com/apache/gora/blob/apache-gora-0.3/gora-core/src/main/java/org/apache/gora/avro/PersistentDatumWriter.java](/Reader)}}
> to Avro's {{SpecificDatumWriter}}, delegating the serialization of the dirty
> field to Avro (but really not desirable to have that field as a main field in
> the entities).
> The proposal is to reintroduce the {{PersistentDatumWriter/Reader}} which
> will serialize the internal fields of the entities.
> This bug affects, for example, Nutch, which loads only some fields in it's
> phases, serializes entities (from Map to Reduce), and when deserializes finds
> all fields as "dirty", independently of what fields were modified in the Map,
> and overwrite all data in datastore (deleting much things: downloaded
> content, parsed content, etc).
> This effect can be seen in
> {{TestPersistentSerialization#testSerderEmployeeTwoFields}}, when debuging in
> {{TestIOUtils#testSerializeDeserialize}}. Proper breakpoints an inspections
> shows that, entities are "equal" when it's fields are equal. This is fine as
> "equal" definition, but another test must be added to check that
> serialization an deserialization keeps the dirty state.
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