[hyc_symas]

> The page says "updates," not "writes." Updates are a constrained form of write where you are writing to an existing key. Updates, importantly, do not affect your index structure, while writes do.

OK, I see your point. It would only have made things even worse for LevelDB here to do an Add/Delete workload because its garbage compaction passes would have had to do a lot more work.

> It is normal for a small B+tree relative to the memory size available on the machine. The "small" was the unrepresentative part of the benchmark, not the "B+tree."

This was 100 million records, and a 5-level deep tree. To get to 6 levels deep it would be about 10 billion records. Most of the branch pages would still fit in RAM; most queries would require at most 1 more I/O than the 5-level case. The cost is still better than any other approach.