json - Explanation of JSONB introduced by PostgreSQL

Question

PostgreSQL just introduced JSONB and it's already trending on hacker news. How is it different from Hstore and JSON previously present in PostgreSQL?

What are its advantages and limitations and when should someone consider using it?

Answer 1

First, hstore is a contrib module, which only allows you to store key => value pairs, where keys and values can only be texts (however values can be sql NULLs too).

Both json & jsonb allows you to store a valid JSON value (defined in its spec).

F.ex. these are valid JSON representations: null, true, [1,false,"string",{"foo":"bar"}], {"foo":"bar","baz":[null]} - hstore is just a little subset compared to what JSON is capable (but if you only need this subset, it's fine).

The only difference between json & jsonb is their storage:

• json is stored in its plain text format, while
• jsonb is stored in some binary representation

There are 3 major consequences of this:

• jsonb usually takes more disk space to store than json (sometimes not)
• jsonb takes more time to build from its input representation than json
• json operations take significantly more time than jsonb (& parsing also needs to be done each time you do some operation at a json typed value)

When jsonb will be available with a stable release, there will be two major use cases, when you can easily select between them:

1. If you only work with the JSON representation in your application, PostgreSQL is only used to store & retrieve this representation, you should use json.
2. If you do a lot of operations on the JSON value in PostgreSQL, or use indexing on some JSON field, you should use jsonb.