The Aurora hash join feature for relational databases has been around for a while now. But unlike MySQL Block Nested Loop algorithm, an Aurora hash join only caters to a specific number of use cases. When implemented with the optimizer properly, they can provide great benefits with certain workloads. Below we’ll see a brief example of a quick win.

This new feature is available in Aurora lab mode version 1.16. Because this is a lab feature, it’s important to make sure to test your queries before upgrading, especially if you are looking to scale up to the new R4 instances before the Superbowl to avoid hitting the same problem I discuss below.

When lab mode is enabled and

hash_join

  is ON, you can verify the optimizer feature from the

optimizer_switch

 variable: