Factual / clj-leveldb

Clojure bindings for LevelDB

This is a self-contained wrapper around LevelDB, which provides all the necessary binaries via leveldbjni.

basic usage

[factual/clj-leveldb "0.1.2"]

To create or access a database, use clj-leveldb/create-db:

clj-leveldb> (def db (create-db "/tmp/leveldb" {}))
#'clj-leveldb/db

This database object can now be used with clj-leveldb/get, put, delete, batch, and iterator.

clj-leveldb> (put db "a" "b")
nil
clj-leveldb> (get db "a")
#<byte[] [B@5e0a614c>

Notice that the value returned is a byte-array. This is because byte arrays are the native storage format for LevelDB, and we haven't defined custom encoders and decoders. This can be done in create-db:

clj-leveldb> (def db (create-db "/tmp/leveldb" 
                       {:key-decoder byte-streams/to-string 
                        :val-decoder byte-streams/to-string}))
#'clj-leveldb/db
clj-leveldb> (get db "a")
"b"

Notice that we haven't defined key-encoder or val-encoder; this is because there's a default transformation between strings and byte-arrays, which assumes a utf-8 encoding. If we wanted to support keywords, or use a different encoding, we'd have to explicitly specify encoders.

Both put and delete can take multiple values, which will be written in batch:

clj-leveldb> (put db "a" "b" "c" "d" "e" "f")
nil
clj-leveldb> (delete db "a" "c" "e")
nil

If you need to batch a collection of puts and deletes, use batch:

clj-leveldb> (batch db {:put ["a" "b" "c" "d"] :delete ["j" "k" "l"]})

We can also get a sequence of all key/value pairs, either in the entire database or within a given range using iterator:

clj-leveldb> (put db "a" "b" "c" "d" "e" "f")
nil
clj-leveldb> (iterator db)
(["a" "b"] ["c" "d"] ["e" "f"])
clj-leveldb> (iterator db "c" nil)
(["c" "d"] ["e" "f"])
clj-leveldb> (iterator db nil "c")
(["a" "b"] ["c" "d"])

Syncing writes to disk can be forced via sync, and compaction can be forced via compact.

Full documentation can be found here.

license

Copyright © 2013 Factual, Inc.

Distributed under the Eclipse Public License, the same as Clojure.