HOW BOOKING.COM SCALED THEIR CUSTOMER REVIEW SYSTEM

Summary from the TLDR Web Dev newsletter

Booking.com scaled its customer review system by sharding reviews across multiple servers using the internal ID of accommodations as the partition key. When it needed to add more machines to the cluster due to increased traffic, it used the Jump Hash Sharding algorithm to minimize the amount of data that needed to be rearranged. This algorithm guaranteed monotonicity, meaning that data was only transferred from old shards to new shards during resharding, avoiding unnecessary data movement.