“Additionally, the new service had a much smaller memory footprint per instance — in the 100s of megabytes — an order of magnitude smaller compared to the 10s of gigabytes our Java implementation needed under peak load to sustain the same throughput and latencies.”
Apple rewrote a Java service in Swift and reports 40% more throughput, 85% less code and memory measured in hundreds of megabytes instead of tens of gigabytes. Any full rewrite cleans out years of cruft. There is no comparison against a tuned rewrite in another language. It is published on Apple’s own Swift blog.