[hibernate-dev] Hibernate OGM mapping for "server side Hibernate Search" via Infinispan Remote

[Sanne Grinovero]

Hi all,

this one is a very desirable feature, yet tricky as there's high
chances of ambiguity and confusion for end users.


# Infinispan Remote indexing

Infinispan embeds the Hibernate Search engine, and uses it to index
data being inserted in any cache having indexing enabled. As you know
Infinispan can be used to store Java POJOs, which get serialized using
JBoss Marshalling - or encoded into Protobuf entries using Infinispan
Protostream as helper layer.

Hibernate OGM supports both modes, one meant for "Infinispan Embedded"
and one for "Infinispan Remote" as that's what each encoding strategy
is suited for.


# Protobuf & indexing

Protobuf is a well defined format with plenty of documentation which
focuses on a "schema" of the encoding; Hibernate OGM is able to
generate such schemas dynamically and will generate encoders and
decoders which follow the encoding guidelines for Java objects.

The meta schema of protobuf is not super flexible, yet there's the
option of annotating the Protobuf schema elements using "annotations"
in comments.
Protostream allows inserting Hibernate Search annotations directly in
these comments and will use them to generate the server side indexing
configuration, implicitly also allowing such properties to be queried
using indexed.

For example you might have this string literally within the comments:
 "@Field(store = Store.YES, analyze = Analyze.YES)"

A full example of schema can be found here [1].
(The Infinispan documentation is a bit sparse on this as they
encourage people to use another code gen tool, best refer to tests as
examples when working for OGM)


# What should OGM users experience?

A naive solution would be to allow people to use the Hibernate Search
annotations on their JPA entities, and we have OGM copy these into the
generated schema; there's a number of problems with that:
 - not all such annotations "translate" equally well [2]
 - there's a mismatch between JPA properties and underlying encoding fields
 - if I run a FullTextQuery do I expect it to work remotely?
 - what if I want to use Hibernate Search locally as well or instead?
 - references to local classes obviously won't work (custom
fieldbridges, analyzers, etc..)

An alternative is to look at these as "indexes" of the underlying
store, so we'd use them to hint the Infinispan server about user
provided hints such as those generated by `javax.persistence.Index`.
I do think this is the cleaner approach, yet has two drawbacks:
 A- I guess ORM might implicitly generate some indexes in its metadata
which the user might not have explicitly asked; e.g. accelerate unique
constraints and foreign keys; it's possible these might not be as
useful as expected in the Infinispan case.
 B- we won't be able to leverage the awesome full-text capabilities :-(

I believe A is something we could ignore for now and revisit if
there's actual demand.

B is also not urgent, yet disappointing limitation as this capability
is a distinguishing feature of this NoSQL. Would we agree that
exposing such full-text capabilities would best be let to an ad-hoc
backend in Hibernate Search 6?


Thanks,
Sanne

1 - http://blog.infinispan.org/2018/02/restful-queries-coming-to-infinispan-92.html
2 - https://github.com/infinispan/infinispan/blob/master/remote-query/remote-query-server/src/main/java/org/infinispan/query/remote/impl/indexing/IndexingMetadataCreator.java#L31