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

• 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 -

• lockKey: string - mandatory
• TTL: number - timeout in ms for the lock. If not given, the TTL given during initialization is considered as the timeout.

Contributions

Contributions are welcome. Please create a pull-request if you want to add new features, test-support or enhance the existing code.

License

MIT