Under the covers Postgres is a giant append only log. This means even when you delete it’s still there, though it does come back through and clean up. Generally this works fine out of the box, but sometimes on large and busy tables you need to do a little yourself.
Over time, conditions change including data growth, usage patterns, and the amount of resources available to the database. Periodic tuning is part of Postgres DBAs role to ensure that things continue to run smoothly. Learn how to optimize performance or get help with a database check up.
If you’re curious to dive even deeper on the features in Postgres 9.5 than just beyond the high level here’s your run through of the improvements to JSONB. These new functions and operators continue to make Postgres and JSON as powerful as ever.