[hibernate-issues] [Hibernate-JIRA] Created: (HSEARCH-880) Discussion on how to support backward / forward compatible serialization layer

[Emmanuel Bernard (JIRA)]

Discussion on how to support backward / forward compatible serialization layer
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                 Key: HSEARCH-880
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HSEARCH-880
             Project: Hibernate Search
          Issue Type: New Feature
          Components: serialization
            Reporter: Emmanuel Bernard


h1. General principles

The serialized message needs the following elements:

* index name: to redirect the flux to the appropriate backend
* serialization provider id: if not present, a cluster must make sure to use the same SerializationProvider for a given IndexManager
* protocol version: today the version is major.minor where the major increase means incompatibility at the stream level, whereas minor means compatibility but with missing features
* stream: this is the SerializationProvider specific byte[]

bq. Do we need a serialization provider id? In other words, do we need to be able to hot-upgrade the SerializationProvider in a cluster?

h1. Exchanging messages in an heterogeneous cluster

h2. Cluster with one way communication (JMS)

In this case the master receives a message and must try and process it.

Receives an index name + serial provider id.
Use the serial provider id to deserialize the message.

If message_major > node_major, the serialization provider fails
If message_minor > node_minor, the serialization provider proceeds but some features might not be supported and the deserialization might fail.

In the minor bump case:

* some feature might not be deserialized and simply ignored. A user is aware of the list of features differences between each node.
* the stream might not be readable by an old version after all due to the use of some new features => Exception

If message_major or message_minor < node_major or node_minor, we use the older protocol deserializer. 

bq. could there ever be a problem where a new HSearch Engine cannot deal with an old HSearch engine's message?

h2. Cluster with two way communication (JMS)

Each time a node A needs to send a message to a node B for the first time. It sends the list of supported SerializationProvider id and for each the list of Versions supported. The first SerializationProvider id is preferred and the latest versions are preferred. 

A version is more recent if majorA > majorB and with majorA = majorB if minorA > minorB.

Node B receives the handshake message and returns the appropriate serialization provider id and version. Subsequent messages are exchanged with this accepted version between A and B

bq. Is the JGroups clustering using multicast to send change messages ie does it know which node it sends the message to to do the handshake?
bq. What happens if B goes down and back up? Does it have a "new" name that uniquely identify it?

h1. API changes

SerializationProvider will need the following adjustments:

* a getSupportedVersions()
* a getSerializer(Version)
* a getDeserializer(Version)

bq. could it be that Serializer / Deserializer / LuceneWorksBuilder lead to the inability to support a version n-1 (by adding of new methods or stuff like that?
 

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