The snapshot plugin adds two new rake tasks that make it easy for you to take a snapshot of your existing (development) database, and restore it again.
Why would you want this?
Imagine you are developing an app. You've spent a few hours filling your development DB with data so that you can design a particular UI scenario. Now, though, you need to design another scenario, which requires a different dataset, and you are loathe to lose the data you so laboriously entered.
The snapshot plugin saves the day:
$ rake db:snapshot
This creates a db/snapshot file (which records all the data in your DB), and a db/snapshot.schema file (which records the state of the schema when the snapshot was taken). At any time, then, you can restore that snapshot:
$ rake db:snapshot:restore
This will erase the existing DB, restore the db/snapshot.schema schema, and then load the data. If there are any pending migrations, it will then run those, and then regenerate the snapshot so that it stays at the latest schema.
You can pass a different snapshot file to use as a parameter, to either task:
$ rake db:snapshot[scenarios/real-estate] ... $ rake db:snapshot:restore[scenarios/telemarketer]
The current version will probably fail when there are foreign key constraints, since the order the tables and rows are restored is not guaranteed to be in any particular order.
Also, even moderately large data sets (e.g. multiple thousands of rows) may result in poor performance during snapshot and restore, since the data is all loaded into memory.