Comment by hyc_symas

Not every.

LMDB is optimized for read-heavy workloads. I make no particular claims about write-heavy workloads.

Because it's so efficient, it can retain more useful data in-memory than other DBs for a given RAM size. For DBs much larger than RAM it will get more useful work done with the available RAM than other DBs. You can examine the benchmark reports linked above, they provide not just the data but also the analysis of why the results are as they are.