Database locks are essential for handling concurrency issues. With databases serving as multi-user shared resources, it’s imperative to manage access ensuring data consistency and integrity.

MySQL Locking Mechanisms

Database locks are essential for handling concurrency issues. With databases serving as multi-user shared resources, it’s imperative to manage access ensuring data consistency and integrity.

Types of Locks

In MySQL, locks can be broadly categorized into:

Global Locks
Table-level Locks
Row-level Locks

Global Locks

Global locks affect the entire database instance. MySQL provides a method for applying a global read lock with the command Flush tables with read lock (FTWRL).

Dangers of Global Locks:

Locking the main database can halt updates, stalling business operations.
Locking a slave database during a backup can cause delays in syncing with the main database.

Table-level Locks

There are two types of table-level locks in MySQL:

Table Locks: Can be applied with the syntax lock tables ... read/write.
Metadata Locks (MDL): Automatically applied when a table is accessed.

Characteristics of MDL:

Multiple threads can read simultaneously.
Write locks are exclusive, ensuring safety during table structural changes.

Row-level Locks

These are the most granular type of locks, targeting individual rows in a table. InnoDB engines implement them, but engines like MyISAM do not.

Deadlocks:

When threads in a system cyclically depend on resources, causing all of them to wait indefinitely, it results in a deadlock. InnoDB provides strategies like waiting until a timeout or initiating deadlock detection.