Explanation of JSONB introduced by PostgreSQL

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.

Peeyush:

The short answer is:

• If you are doing a lot of JSON manipulation inside PostgreSQL, such as sorting, slicing, splicing, etc., you should use JSONB for speed reasons.
• If you need indexed lookups for arbitrary key searches on JSON, then you should use JSONB.
• If you are doing neither of the above, you should probably use JSON.
• If you need to preserve key ordering, whitespace, and duplicate keys, you should use JSON.

For a longer answer, you'll need to wait for me to do a full "HowTo" writeup closer to the 9.4 release.

A simple explanation of the difference between json and jsonb (original image by PostgresProfessional):

SELECT '{"c":0,   "a":2,"a":1}'::json, '{"c":0,   "a":2,"a":1}'::jsonb;          json          |        jsonb ------------------------+---------------------  {"c":0,   "a":2,"a":1} | {"a": 1, "c": 0} (1 row)

• json: textual storage «as is»
• jsonb: no whitespaces
• jsonb: no duplicate keys, last key wins
• jsonb: keys are sorted

More in speech video and slide show presentation by jsonb developers. Also they introduced JsQuery, a pg.extension that provides the powerful jsonb query language.