Imagine you have news feed which may contains audio, video, links, and comments
For newsfeed(NF), we can have a relational data base which consist of the nf_id, creation date, last update, blob of content/text [lets keep the links in the text so the user will redirect when clicked], creator id. I will add another id called meta data id/metaUUID to refer to the meta data for this new feed.

The meta data (MD)does not have a fixed schema. Lets say it has metaUUID, #of likes, #dislikes, status, list<id's of comments>, list<id's of audio videos> the id's are identified for content in CDN already uploaded by the creator of the post. Please add attributes which you think are relevant.

Now, I have two questions.

Can NF be placed in sql based data base while its Metadata (MD) is in some no sql based data base. SInce the schema is not well defined and the columns are ever expanding, the comments o for example, what woud be the suitable choice
Non sql or SQL. if non sql, how is semi structure data base like cassandra compare to key value store like Redis, MemCache.

Second question, Since now the app server now deal with two data bases types to fetch news feed, newsfeed from sql and newsfeed meta data from non sql, the handling and association will happen in the application itself. Is there a pros and cons of it. Please share your view

If you have alternative suggesstion, please do share