[hibernate-dev] Proposal for a Redis module in Hibernate OGM

[Gunnar Morling]

Hi Mark,

Many thanks for giving this a try; Your work looks impressive, it's very
advanced for an initial dialect contribution, covering many advanced cases
already. So kudos for that!

Please find some remarks and questions below.

Cheers,

--Gunnar


2015-07-17 17:16 GMT+02:00 Mark Paluch <mpaluch at paluch.biz>:

> Hi there,
>
> I created a Redis module for Hibernate OGM, based on OGM 4.2. Redis is a
> Key-Value store supporting Lists, Hashes (Maps), Sorted Sets, ...
>
> I took the Infinispan/CouchDB approach storing entities and associations as
> JSON documents within Redis Hashes. A Map<Object, Map<Object, Object>>
> corresponds with a Redis Hash.
>
> The entity table maps to the Hash Id, the entity Id to the key of the hash
> and the set of columns is enclosed within a JSON (currently). Supported
> features are:
>
> * Composite Id's
> * Embedded associations
> * External associations
>

* I saw you create a hash per entity type, using the ids as keys within
this hash and a JSON document modelling the properties of a given entity
instance.

Have you considered to store JSON documents on the "top-level" instead?
This would require to encode the table name into the key as well (similar
to as we do it for CouchDB): "Order:123" -> ... . The reason I am asking is
that I am wondering whether it may be a source of contention and/or whether
it may pose scaling issues if all entities of one type are stored within a
single hash.

Using JSON for the actual entity contents seems reasonable and a common
approach in the Redis world from what I've read, so +1 for doing this from
me. How would the "more native" approach look like you describe below?
Would we have to serialise everything ourselves into String/byte[]? If so,
I am not sure whether that's of much usefulness actually and I'd be
inclined to go the JSON route exclusively. As you say, it also works nicely
for hierarchical structures.

* The id is used as key and also part of the JSON value. Could it be
removed from the latter?

* Do you have any ideas how Redis-specific structures could be exposed
which do not map exactly to entities, e.g. Lists stored directly via some
key?

* Our option system could be used to expose specific settings such as TTL
for given entities

* Is there any form of transaction support in Redis we could leverage?

and I guess many more, that I'm currently not aware of :-)
>
> There are various ways (JSON, Java-serialized simulating Documents) how to
> store data within Redis.
> Another approach could be storing Tuples within Redis more native, since
> they are in the end Maps, somehow. However, mapping tuples to Redis fit a
> native storage but raises questions about Id's, limited data type support
> (there is no equivalent for nested lists/maps). So the more native approach
> would require distributing data amongst various data types, depending on
> the supported features, and would require more IO's.
>
> My impl can be used to interoperate with other clients from the C, Ruby,
> Python, Node.js, ... worlds. The JSON is clean and does not look awkward on
> the first look.
>
> The current code can be found below
> https://github.com/mp911de/hibernate-ogm/tree/redis. Most TCK tests pass,
> only some 15 tests fail. Mostly due to enum and JTA support. Couldn't
> figure out, how to fix it, so need your help to figure it out.
>

I'll take a closer look at your change asap. Could you create a pull
request from your branch against the upstream repo? Then we can have a
discussion right there.

Hope, I made you hungry for the Redis OGM module. Let's start a discussion
> based on my proposal for inclusion and let's see, where we end up.
>

Yep, it looks very promising and I think it'd be great to have support for
Redis in OGM :) We'll need your continued help though to make it happen and
evolve it in the future as Redis itself and OGM core advance.

Best regards, Mark
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