If you look at the MDBM page you'll notice that they currently benchmark against LevelDB, BerkeleyDB, and Kyoto Cabinet. What I was suggesting involves the same theme but better, newer competition.
I agree that it's an apples to oranges comparison in any case.
The timings they give there can only make sense on a fast SSD or when the database they benchmark on is completely cached.
It's an apples-to-oranges comparison only of MDBM wins significantly against LMDB. If they are comparable in timing, or e.g. MDBM is 20% faster, then it would be an apples-to-apples comparison, MDBM having 20% speed advantage, and LMDB having every other possible advantage (memory safety, ACIDity, ordered retrieval, multiple databases, etc.)
LMDB is truly, incredibly, really marvelous. On 64-bit it comes close to being the end-all-be-all local KV-store. If your databases are not more than a few tens of megs each, the same is true for 32-bit processors as well.
Sure. But you only have 2-3GB of usable address space, and if your app has a lot of other variables to work with, there's not much space left over.
I should note that in LMDB 1.0 we'll have dynamic unmapping and remapping, to allow 32-bit machines to work with larger DBs. (There's still a significant performance cost for this. It's only being done to allow folks to use the same code on 32 and 64.)
If you're interested in building a distributed DB on top of LMDB, I took care of part of the problem (replication/consistency) in my flotilla library at
Basically I'm just layering the raft consistency algorithm on top of LMDB. Both systems single-thread write transactions for consistency, so there's some mechanical sympathy. Doesn't mandate any specific data model or even a client-server network transport, it's basically a replicated embedded DB. Anyone could build replicated redis on top of it or a Cassandra clone if they want to get into managing shards/rings.
For redis, there's already ardb, ledisdb, redis-NDS, and a few other redis clones that support LMDB. We also already have memcacheDB on LMDB, as well as HyperDex with LMDB.
I haven't looked closely at Cassandra since it's in java, and after I didn't find a simple backend plugin API I didn't look any further.
I agree that it's an apples to oranges comparison in any case.