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Documentation on LMDB says it is really fast. I found this performance benchmark which compares it to the BoltDB and Badger. According to it, LMDB is slightly faster than BoldDB, but both lose to Badger.
It would be interesting to make our own benchmarks, but to compare LMDB with LevelDB which also has a binding to Common Lisp. But that is a story for another day.
Here is a fixed and slightly modified example from the CL wrapper's README. It just writes a string by the key and reads it back:
POFTHEDAY> (let ((env (lmdb:make-environment #p"./the-database/"))) (lmdb:with-environment (env) ;; Create a transaction (let ((txn (lmdb:make-transaction env))) (lmdb:begin-transaction txn) ;; Create a database access object (let ((db (lmdb:make-database txn "db"))) (lmdb:with-database (db) ;; Here is how we can write some data to the storage (lmdb:put db "the key" "The string") ;; and read it back: (let ((vec (lmdb:get db "the key"))) (print vec))))))) ;; Pay attention, the data is returned as a vector and your ;; app have to interpret it: #(84 104 101 32 115 116 114 105 110 103) POFTHEDAY> (babel:octets-to-string *) "The string"
What is interesting, I found this library was used in this Wiki software, written in Common Lisp: Antimer.
But LMDB backend was removed from Antimer at some moment and replaced with SQLite. Most probably because it needed the full power of SQL instead of simple key-value queries.
To finalize, this LMDB binding would be a good solution for small apps which makes simple queries and need a high-performance and low latency.
BTW, the LMDB's repository needs some love because there are some hanging pull requests and a few unanswered issues. Does somebody know how does Fernando Borretti feels himself? Maybe he needs some help?