High Performance PostgreSQL for Rails

Online Data Migration

pgslice is designed for online (or “zero downtime”) migrations. As you learned earlier, this means you don’t need to stop PostgreSQL or disconnect clients from accessing the table while you migrate data. Since row copying happens while PostgreSQL is running, concurrent requests continue to be served. While this is a great benefit, this approach comes with trade-offs like increased operational risk due to the increased load placed on the server during the row copying.

pgslice has commands to copy data rows from the original table into the intermediate table you just created. This approach can be called “nondestructive” because it doesn’t modify the original data. With nondestructive approaches, we’re able to roll back the ...