Sql-lock NPM | npm.io

sql-lock

sql-lock is a distributed lock manager for NodeJS, which works with the help of a MySQL Server.

Motivation

There are a lot of use cases that require an exclusive access to a resource. In a distributed system, with several containers running the same piece of code in parallel, achieving this can get quite difficult.

sql-lock solves this problem, by allowing you to get distributed locks in your code from a MySQL server.

How does it work

Simple Locking Mechanism

On initialization it creates a table lockings containing a column id.
Whenever someone tries to get a lock, a transaction is started in MySQL and an entry is created with id equal to lock key.
This gives a row lock to the transaction, which prevents someone from trying to get the same lock again.
To release the lock, the transaction is committed and the row deleted. Anyone else trying to get a lock with same lock key can then proceed.
More information can be found in our blog posts -
- https://medium.com/uc-engineering/pessimistic-locking-for-a-distributed-system-part-1-cc85c755c357
- https://medium.com/uc-engineering/pessimistic-locking-for-a-distributed-system-part-2-f2d224567284

Requirements

MySQL Server
NodeJS > 6

Installation

npm install sql-lock

Usage

Initialization

const sqlLock = require('sql-lock');
sqlLock.initialize(MysqlURI, { locking_ttl: 30000 });

MysqlURI - MySQL connection string - Eg mysql://travis@127.0.0.1:3306/test.
Options:
- locking_ttl - Default timeout for your locks (in ms)

This will automatically create a table named locking in the database.

Code

const sqlLock = require('sql-lock');
const lockReleaser = await sqlLock.getLock('lock_key', 3000);
await someAsyncWork();
lockReleaser(); //Release lock

This code gets a lock on the key lock_key which is released when either lockReleaser function is called or the lock times out.

If someone else tries to get a lock with the same key, they will have to wait till the first lock is released.

getLock accepts two parameters -