Arenas are just heaps, and subject to all the same problems. It's true that in the LSM use case in question (and I need to point out that databases are not my

Arenas are just heaps, and subject to all the same problems. It's true that in the LSM use case in question (and I need to point out that databases are not my area!) there is a clear "flush" operation that will put a limit on how much heap churn and fragmentation you need to tolerate. And maybe that's an answer that makes skiplists more desirable in this context. But things like long-lived app data and language runtimes don't have that, and skiplists turn into headaches. A simpler consequence of the same problem: I mostly work in embedded stuff and skiplists are pretty much a non-starter as they can't easily be made intrusive without a bunch of waste.