Crystal binding for LevelDB.
LevelDB is a fast key-value storage library written at Google that provides an ordered mapping from string keys to string values.
Debian:
sudo apt-get install libleveldb-dev libleveldb1v5 libsnappy1v5
dependencies:
leveldb:
github: "crystal-community/leveldb"
version: "~> 0.2.0"require "leveldb"
# Create DB (if does not exist yet) and open
db = LevelDB::DB.new("./db")
# Put, get, delete
db.put("name", "Sergey")
db.get("name") # => "Sergey"
db.delete("name")
db.get("name") # => nil
# [], []= methods work the same
db["city"] = "Berlin"
db["city"] # => "Berlin"
# Iterate through all the keys
db.each do |key, val|
puts "#{key} = #{val}"
end
# Close database
db.close
db.closed? # => true
db.opened? # => false
# Close the database and remove all the data
db.destroy
# Remove all the keys, keep the database open
db.clearApply a atomic batch of of operation to the key-value store.
require "leveldb"
db = LevelDB::DB.new("./db")
begin
batch = LevelDB::Batch.new
batch.put("name","Martin")
batch.put("age","25")
batch.put("location","Bariloche")
batch.delete("age")
# write batch to the db in atomic way
db.write(batch)
puts db.get("name")
puts db.get("age") # nil
puts db.get("location")
ensure
# free memory
batch.destroy
# close the database
db.close
end
Snapshots provide consistent read-only views over the entire state of the key-value store.
db = LevelDB::DB.new("./db")
db.put("a", "1")
db.get("a") # => "1"
snapshot = db.create_snapshot
db.delete("a")
db.get("a") # => nil
db.set_snapshot(snapshot)
db.get("a") # => "1"
db.unset_snapshot
db.get("a") # => nilThere is performance comparison of LevelDB and other stores from Kiwi project.
- greyblake Sergey Potapov - creator, maintainer
- twisterghost Michael Barrett