I'm looking to migrate from Postgres 9.3 to 9.4, and have a lot of data in JSON columns. While it's fine, I wanted to have a look at migrating to the more efficient column storage (which JSONB seems to be — a really exciting piece of tech!).

To actually migrate, I want to know migration characteristics for something like

```
ALTER TABLE table_with_json
    ALTER COLUMN my_json
    SET DATA TYPE jsonb
    USING my_json::jsonb;

```

(from [this helpful question](https://stackoverflow.com/questions/28202158/postgresql-migrating-json-to-jsonb)).

Ideally, it would be good to know how long it takes to migrate 1mil and 10mil entries, and how it scales.

While I can get these numbers myself, I thought this question might be helpful for others. If I end up trying this out myself, I'll be sure to provide an answer for others, but not sure when that'll happen.