You are probably using LevelDB without knowing it since it's part of the Chrome browser (exposed as IndexedDB). If we compare it to Redis, it's even lighter, has more reliable writes and, unlike Redis, you don't store your entire data in memory but in the file system. Another difference is Redis has more data structures (sets, lists, etc.) that LevelDB is lacking. The similarity is that both store key-value pairs and both can save JSON. C/C++ library.
Github | Documentation is bundled with the source
Keys and values are arbitrary byte arrays.
Data is stored sorted by key.
Callers can provide a custom comparison function to override the sort order.
The basic operations are Put(key,value), Get(key), Delete(key).
Multiple changes can be made in one atomic batch.
Users can create a transient snapshot to get a consistent view of data.
Forward and backward iteration is supported over the data.
Data is automatically compressed using the Snappy compression library.
External activity (file system operations etc.) is relayed through a virtual interface so users can customize the operating system interactions.
This is not a SQL database. It does not have a relational data model, it does not support SQL queries, and it has no support for indexes.
Only a single process (possibly multi-threaded) can access a particular database at a time.
There is no client-server support builtin to the library. An application that needs such support will have to wrap their own server around the library.
What situations is it good for?
* Whenever you need an easy way to persist data without worrying about RAM but with speed very close to memory access
* Smartphones, Raspberry Pi or similar small device
* Offline web apps - if you use LevelDB on the server you might be able to use the same code for the browser storage (IndexedDB)
* Building block for a database. LevelDB (or a variant) is used in BigTable, Hadoop’s HBase, Cassandra and Riak.
npm install [levelup](https://www.npmjs.com/package/levelup): most popular node package for LevelDB
var levelup = require('levelup')
var db = levelup('./mydb')
db.put('post!' + Date.now(), {author: 'fred', title: 'Angular', content: '<p> bla bla bla </p>'}, {encoding:'json'}, function (err) {
if (err) return console.log('Ooops!', err) // some kind of I/O error
db.put('post!' + Date.now(), {author: 'fred', title: 'Responsive Design', content: '<p> blu blu blu </p>'}, {encoding:'json'}, function (err) {
if (err) return console.log('Ooops!', err) // some kind of I/O error
// to get a stream of all posts in reverse chronological order
db.createReadStream({ reverse: true, encoding: 'json' })
.on('data', function (data) {
console.log(data.key, '=', data.value)
})
.on('error', function (err) {
console.log('Oh my!', err)
})
.on('close', function () {
console.log('Stream closed')
})
.on('end', function () {
console.log('Stream ended')
})
})
});
API is very simple (basic CRUD ops). Keys must be unique, hence the use of Date.now() (which returns a ridiculous number of seconds representing now); keys are strings.
Last modified 16 December 2024