memdown

What is memdown?

memdown is an in-memory backend for the LevelUP library, which provides a simple and efficient way to store and retrieve data in memory. It is particularly useful for testing and development purposes where persistence is not required.

What are memdown's main functionalities?

Basic Operations

This feature allows you to perform basic operations such as putting, getting, and deleting key-value pairs in the in-memory database.

const levelup = require('levelup');
const memdown = require('memdown');

const db = levelup(memdown());

// Put a value
await db.put('key', 'value');

// Get a value
const value = await db.get('key');
console.log(value); // 'value'

// Delete a value
await db.del('key');

Batch Operations

This feature allows you to perform multiple operations in a single batch, which can be more efficient than performing them individually.

const levelup = require('levelup');
const memdown = require('memdown');

const db = levelup(memdown());

// Perform batch operations
await db.batch()
  .put('key1', 'value1')
  .put('key2', 'value2')
  .del('key1')
  .write();

// Get a value
const value = await db.get('key2');
console.log(value); // 'value2'

Stream Operations

This feature allows you to create streams to read data from the database, which can be useful for processing large amounts of data efficiently.

const levelup = require('levelup');
const memdown = require('memdown');

const db = levelup(memdown());

// Put some values
await db.put('key1', 'value1');
await db.put('key2', 'value2');
await db.put('key3', 'value3');

// Create a read stream
const stream = db.createReadStream();

stream.on('data', ({ key, value }) => {
  console.log(`${key}: ${value}`);
});

stream.on('end', () => {
  console.log('Stream ended');
});

Other packages similar to memdown

leveldown

leveldown is a LevelDB backend for the LevelUP library. Unlike memdown, which stores data in memory, leveldown stores data on disk using Google's LevelDB. This makes it suitable for applications that require persistent storage.

rocksdb

rocksdb is a backend for the LevelUP library that uses Facebook's RocksDB, a high-performance, persistent key-value store. It offers better performance and more features compared to LevelDB, making it suitable for high-throughput applications.

sqlite3

sqlite3 is a backend for the LevelUP library that uses SQLite, a self-contained, serverless, and zero-configuration SQL database engine. It provides a more feature-rich and flexible storage solution compared to memdown, with support for complex queries and transactions.

README

memdown

In-memory abstract-leveldown store for Node.js and browsers.

Example

If you are upgrading: please see the upgrade guide.

const levelup = require('levelup')
const memdown = require('memdown')

const db = levelup(memdown())

db.put('hey', 'you', (err) => {
  if (err) throw err

  db.get('hey', { asBuffer: false }, (err, value) => {
    if (err) throw err
    console.log(value) // 'you'
  })
})

Your data is discarded when the process ends or you release a reference to the store. Note as well, though the internals of memdown operate synchronously - levelup does not.

Browser support

Data types

Unlike leveldown, memdown does not stringify keys or values. This means that in addition to Buffers, you can store any JS type without the need for encoding-down. For keys for example, you could use Buffers or strings, which sort lexicographically, or numbers, even Dates, which sort naturally. The only exceptions are null and undefined. Keys and values of that type are rejected.

const db = levelup(memdown())

db.put(12, true, (err) => {
  if (err) throw err

  db.createReadStream({
    keyAsBuffer: false,
    valueAsBuffer: false
  }).on('data', (entry) => {
    console.log(typeof entry.key) // 'number'
    console.log(typeof entry.value) // 'boolean'
  })
})

If you desire normalization for keys and values (e.g. to stringify numbers), wrap memdown with encoding-down. Alternatively install level-mem which conveniently bundles levelup, memdown and encoding-down. Such an approach is also recommended if you want to achieve universal (isomorphic) behavior. For example, you could have leveldown in a backend and memdown in the frontend.

const encode = require('encoding-down')
const db = levelup(encode(memdown()))

db.put(12, true, (err) => {
  if (err) throw err

  db.createReadStream({
    keyAsBuffer: false,
    valueAsBuffer: false
  }).on('data', (entry) => {
    console.log(typeof entry.key) // 'string'
    console.log(typeof entry.value) // 'string'
  })
})

Snapshot guarantees

A memdown store is backed by a fully persistent data structure and thus has snapshot guarantees. Meaning that reads operate on a snapshot in time, unaffected by simultaneous writes. Do note memdown cannot uphold this guarantee for (copies of) object references. If you store object values, be mindful of mutating referenced objects:

const db = levelup(memdown())
const obj = { thing: 'original' }

db.put('key', obj, (err) => {
  obj.thing = 'modified'

  db.get('key', { asBuffer: false }, (err, value) => {
    console.log(value === obj) // true
    console.log(value.thing) // 'modified'
  })
})

Conversely, when memdown is wrapped with encoding-down it stores representations rather than references.

const encode = require('encoding-down')

const db = levelup(encode(memdown(), { valueEncoding: 'json' }))
const obj = { thing: 'original' }

db.put('key', obj, (err) => {
  obj.thing = 'modified'

  db.get('key', { asBuffer: false }, (err, value) => {
    console.log(value === obj) // false
    console.log(value.thing) // 'original'
  })
})

Test

In addition to the regular npm test, you can test memdown in a browser of choice with:

npm run test-browser-local

To check code coverage:

npm run coverage

Contributing

Level/memdown is an OPEN Open Source Project. This means that:

Individuals making significant and valuable contributions are given commit-access to the project to contribute as they see fit. This project is more like an open wiki than a standard guarded open source project.

See the Contribution Guide for more details.

Big Thanks

Cross-browser Testing Platform and Open Source ♥ Provided by Sauce Labs.

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License

MIT © 2013-present Rod Vagg and Contributors.

Changelog

[4.1.0] - 2019-06-28

Changed

• Upgrade nyc devDependency from ^13.2.0 to ^14.0.0 (#182) (@vweevers)

Added

• Support seeking (#184) (@MeirionHughes)