[hibernate-issues] [Hibernate-JIRA] Commented: (HSEARCH-836) Evaluate the need to send the writing schema over with the message

[Sanne Grinovero (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HSEARCH-836?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=43185#comment-43185 ] 

Sanne Grinovero commented on HSEARCH-836:
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I'm wondering if we could send it optionally, this would need some way for the server to answer with a "I need the schema".
We could have it send the schema once when the backend starts up, but this doesn't help if the master is restarted; it would be good if the master could store it in it's local filesystem.
Could an "availables schema store" be shared? A database table, an Infinispan entry, a jar containing resources to make an old version "forward compatible" to be deployed on the master.

These look complex, a simple alternative could be to send it periodically every N messages, where N can be 1 (all), 0 (never) or another positive number. If this was JMX configurable, admins could force it to send an updated schema to masters when they need.

Even simpler: we support it only on demand (the "I need the schema" request from the server), and in the JMS case in which we can't answer people will have to upgrade the master first.

> Evaluate the need to send the writing schema over with the message
> ------------------------------------------------------------------
>
>                 Key: HSEARCH-836
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HSEARCH-836
>             Project: Hibernate Search
>          Issue Type: Bug
>          Components: serialization
>    Affects Versions: 4.0
>            Reporter: Emmanuel Bernard
>
> Avro knows to read a message serialized by a different writer assuming certain conditions described in their spec http://avro.apache.org/docs/1.5.1/spec.html
> But both reader and writer schema should be provided up deserialization 
> GenericDatumReader(Schema writer, Schema reader, GenericData data)
> Should we embed the schema with each message? It looks like a significant payload.
> If we don't, we can use the major.minor version numbers that are before the avro stream. But that will only work if the receiver is more recent that the writer.
> In all case, we need a prototype to test backward compatibility.

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