femami

json_fdw to Citus DB or any other PostgreSQL based distributed database, is like json serde to Hive.

So, I think you should probably compare the json_fdw to json serde, and Citus DB to Hive.

I think if your data is append-only, this should work good enough. You implement your data appending logic, and you use json_fdw for querying your data. But this requires starting PostgreSQL service, I'm not sure if this is acceptable in your application or not.

Loading into database usually means transforming the data such that the data is stored as database's internal format. For example, using "LOAD DATA ..." in MySQL or "COPY ... FROM ..." in PostgreSQL.

Here, you aren't storing the data in the database. You don't have to take any additional action to sync the file and db when you add rows to the file, so it's not loaded into the database.