PostgreSQL allows its functionality to be extended with additional modules called extensions. Many of these extensions aren't installed by default in PostgreSQL, because they aren't part of its core and mainly because they are specific to a limited audience. In addition, some extensions are experimental, but nothing prevents their use.

Heroku Postgres provides some interesting extensions for data types, functions, statistics, index types, languages, searches, and many others. In the next sections, you will learn about each of these extensions, with simple samples, and you will understand how they work.

The first step to get started is to discover the list of available extensions in your database; it may vary according your database plan. You should do it using the following command:

$ echo 'show extwlist.extensions' | heroku pg:psql --app your-app-name
---> Connecting to HEROKU_POSTGRESQL_CHARCOAL_URL (DATABASE_URL)
extwlist.extensions 
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