Implement cache module for Redis

[xvrl]

Can probably reuse most of the Memcached code.

@estliberitas offered to work on this.

[estliberitas]

Yep, I'm working on it. Testing right now. I've got some questions and will write them down if can't find an answer by myself.

[estliberitas]

As far as I understand it, in order to implement a separate cache module which works with Redis, we should move CacheProvider, Cache, CacheStats to druid-common module, correct?

If so, we would need following changes:

1. Add server-metrics as dependency to druid-common thus Cache.doMonitor(...) has ServiceEmitter as argument (or refactor this to not depend on server-metrics)
2. Remove @JsonSubTypes from CacheProvider and instead register subtypes in CacheModule via exported Jackson module -SetupContext.registerSubtypes(...).

I have a problem with backwards compatibility: since I moved CacheProvider to druid-common I can't set default implementation class in @JsonTypeInfo annotation. If there any way to setup default implementation from code or do something else to set LocalCacheProvider as default CacheProvider?

[estliberitas]

UPDATE: I just looked at code and found that mysql-metadata-storage module has druid-server as it's dependency. If so, then Redis cache module can have this dependency too and nothing above is needed, correct?

Will I still be able to use SetupContext.registerSubtypes(RedisCacheProvider.class) in case that @JsonSubTypes over CacheProvider is left as is?

[xvrl]

@estliberitas yes, you can depend on druid-server to get the ball rolling on this. We can revisit later if that becomes a problem.

registerSubtypes should be enough to make it work yes, but you should test to see if you can stil use both memcached and redis. If not we might have to manually register all the cache types instead of using annotations.

[estliberitas]

@xvrl @fjy It may be an odd question, but, how can I create a custom build in current master branch?

With 0.8.1 it was simple with extensions-distribution module. Now it's removed, and I do not understand how can I create a build and include my new extension (resides in extensions/redis-cache) into it.

[gianm]

@estliberitas if you do a mvn install then that will build extensions into the distribution/target/extensions/ directory.

[gianm]

The extensions system was reworked in #1638

[estliberitas]

@gianm I figured that out, but still can't understand how can I add my new extension to others that are bundled.

[guobingkun]

Hi @estliberitas, you can add an entry here https://github.com/druid-io/druid/blob/master/distribution/pom.xml#L95

[estliberitas]

@guobingkun Well, my extension is not on Maven (I'm currently developing it), is it OK?

[guobingkun]

@estliberitas , that's fine, When you do mvn install, your extension will be installed in the local repository, pull-deps will pull your extension from there.

[estliberitas]

@guobingkun Thanks, it worked!