Terracotta open sourced it’s core offheap library earlier this year. Despite being a Terracotta project, it: doesn’t use byte code engineering, doesn’t require running a modified JVM. Despite being an offheap library, it: doesn’t use non-standard APIs or JNI, doesn’t do reflection on core JDK types. It does however: provide a library of maps and caches with significantly sub-linear per key heap overheads, scale up to 6TB in a single node and 1TB in a single map. What follows will be an explanation of how well understood CS concepts from managed and unmanaged programing environments combine to produce a stable, reliable, and useful library. There is no secret sauce here, and the source is no longer secret.