Tagged articles

MDL

5 articles · Page 1 of 1

Aug 17, 2026 · Databases

Does Adding an Index Lock the Table? JD Interview Deep Dive (Full Score Edition)

The article explains that whether adding an index locks a MySQL table depends on the version and DDL algorithm—MySQL 5.5 and earlier lock the whole table, 5.6‑5.7 use Online DDL with brief metadata locks, and 8.0+ can create secondary indexes instantly without locking, while primary, unique, and full‑text indexes always require locking.

COPYINPLACEINSTANT

0 likes · 10 min read

Does Adding an Index Lock the Table? JD Interview Deep Dive (Full Score Edition)

Aikesheng Open Source Community

May 20, 2025 · Databases

How to Diagnose and Resolve MySQL MDL Lock Blocking DDL Operations

This article walks through the background, reproduction steps, investigation methods, and concrete solution for MySQL metadata lock (MDL) issues that cause DDL statements to hang, and provides practical tips to prevent similar lock problems in production environments.

DDLMDLMetadata Lock

0 likes · 10 min read

How to Diagnose and Resolve MySQL MDL Lock Blocking DDL Operations

Aikesheng Open Source Community

Apr 26, 2022 · Databases

Understanding MySQL Metadata Locks (MDL) and Their Impact on DDL/DML Operations

The article explains MySQL's metadata lock (MDL) mechanism, shows how to enable its instrumentation, demonstrates various lock scenarios with SELECT, INSERT and ALTER statements, and provides guidance on diagnosing and resolving MDL‑related blocking issues.

DDLDMLMDL

0 likes · 12 min read

Understanding MySQL Metadata Locks (MDL) and Their Impact on DDL/DML Operations

Aikesheng Open Source Community

Apr 14, 2020 · Databases

Understanding MySQL MDL Locks: Types, Structures, and Debugging Techniques

This article provides an in-depth analysis of MySQL's Metadata Lock (MDL) system, detailing lock types, data structures, acquisition, upgrade, downgrade processes, compatibility matrices, and practical debugging via custom print functions, with code examples and performance schema observations.

MDLMySQLdebugging

0 likes · 28 min read

Understanding MySQL MDL Locks: Types, Structures, and Debugging Techniques

Tencent Database Technology

Nov 24, 2017 · Databases

MySQL Metadata Lock (MDL): Usage, Implementation, Deadlock Detection, and Lock‑Free Optimizations

This article explains MySQL's Metadata Lock (MDL) subsystem, describing how MDL protects metadata, the lock types and modes, the transaction‑level implementation introduced in MySQL 5.5 and refined in 5.7, the lock acquisition and release algorithms, deadlock detection mechanisms, and the lock‑free hash table used to store lock objects.

Lock-Free HashMDLMetadata Lock

0 likes · 25 min read

MySQL Metadata Lock (MDL): Usage, Implementation, Deadlock Detection, and Lock‑Free Optimizations