If you're not doing random writes (that is, random keys) an LSM has no write amplification, it essentially becomes a sorted list of SSTables. I can't think of

If you're not doing random writes (that is, random keys) an LSM has no write amplification, it essentially becomes a sorted list of SSTables. I can't think of any OLTP application where the writes are not random (in the sense of relative position in the key space). Either your primary keys are, or at least all your indexes are. Write amplification is not an issue if sequential writes are orders of magnitude faster than random writes, which is usually the case, so even with that LSMs come out ahead. Also if your application is read-heavy, you can tune the LSM parameters to have fewer levels (at the cost of more compaction traffic). With B-trees, you have to chase a fixed depth of log_{page size}.