go-mysql-lock

go-mysql-lock provides locking primitive based on MySQL's GET_LOCK Lock names are strings and MySQL enforces a maximum length on lock names of 64 characters.

Use cases

Though there are mature locking primitives provided by systems like Zookeeper and etcd, when you have an application which is primarily dependent on MySQL for its uptime and health, added resiliency provided by systems just mentioned doesn't add much benefit. go-mysql-lock helps when you have multiple application instances which are backed by a common mysql instance and you want only one of those application instances to hold a lock and do certain tasks.

Installation

go get github.com/sanketplus/go-mysql-lock

Example:

package main

import (
    "context"
    "database/sql"
    
    _ "github.com/go-sql-driver/mysql"
    "github.com/sanketplus/go-mysql-lock"
)

func main() {
	db, _ := sql.Open("mysql", "root@tcp(localhost:3306)/dyno_test")

	locker := gomysqllock.NewMysqlLocker(db)

	lock, _ := locker.Obtain("foo")
	lock.Release()
}

Features

Customizable Refresh Period

Once the lock is obtained, a goroutine periodically (default every 1 second) keeps pinging on connection since the lock is valid on a connection(session). To configure the refresh interval

locker := gomysqllock.NewMysqlLocker(db, gomysqllock.WithRefreshInterval(time.Millisecond*500))

Obtain Lock With Context

By default, an attempt to obtain a lock is backed by background context. That means the Obtain call would block indefinitely. Optionally, an Obtain call can be made with user given context which will get cancelled with the given context.

The following call will give up after a second if the lock was not obtained.

locker := gomysqllock.NewMysqlLocker(db)
ctxShort, _ := context.WithDeadline(context.Background(), time.Now().Add(time.Second))
lock, err := locker.ObtainContext(ctxShort, "key")

Obtain Lock With (MySQL) Timeout

MySQL has the ability to timeout and return if the lock can't be acquired in a given number of seconds. This timeout can be specified when using ObtainTimeout and ObtainTimeoutContext. On timeout, ErrMySQLTimeout is returned, and the lock is not obtained.

The following call will give up after a second if the lock was not obtained, using MySQL timeout option:

locker := gomysqllock.NewMysqlLocker(db)
lock, err := locker.ObtainTimeout("key", 1)

Know When The Lock is Lost

Obtained lock has a context which is cancelled if the lock is lost. This is determined while a goroutine keeps pinging the connection. If there is an error while pinging, assuming connection has an error, the context is cancelled. And the lock owner gets notified of the lost lock.

context := lock.GetContext()

Compatibility

This library is tested (automatically) against MySQL 8 and MariaDB 10.1, and it should work for MariaDB versions >= 10.1, MySQL versions >= 5.6, and Vitess versions >= 15.0.

Note that GET_LOCK function won't lock indefinitely on MariaDB 10.1 / MySQL 5.6 and older, as 0 or negative value for timeouts are not accepted in those versions. This means that in MySQL <= 5.6 / MariaDB <= 10.1 you can't use Obtain or ObtainContext. To achieve a similar goal, you can use ObtainTimeout (and ObtainTimeoutContext) using a very high timeout value.