Why MySQL Auto‑Increment IDs Aren’t Always Sequential (And How to Optimize Them)

Understanding MySQL’s auto‑increment mechanism reveals why IDs can become non‑sequential due to storage differences, transaction rollbacks, unique key conflicts, and batch inserts, and shows how lock‑mode settings and MySQL 8.0 improvements can optimize performance and maintain consistency.

Batch Insertauto_incrementlock mode

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Why MySQL Auto‑Increment IDs Aren’t Always Sequential (And How to Optimize Them)

Liangxu Linux

Jun 7, 2023 · Databases

Why MySQL Auto‑Increment IDs Aren’t Always Sequential (And How to Fix It)

This article explains how MySQL stores and updates auto‑increment values, why gaps appear after failed inserts, unique‑key conflicts, transaction rollbacks or batch operations, and how different innodb_autoinc_lock_mode settings and MySQL 8.0 improvements can mitigate the issue.

Database DesignInnoDBauto_increment

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Why MySQL Auto‑Increment IDs Aren’t Always Sequential (And How to Fix It)

Art of Distributed System Architecture Design

Mar 17, 2016 · Databases

Changes in InnoDB Auto‑Increment Locking Mechanism After MySQL 5.1.22 and Configuration Options

The article explains how InnoDB’s auto‑increment handling changed after MySQL 5.1.22—from using a table lock to a lightweight mutex for predictable‑row inserts—and details the three innodb_autoinc_lock_mode settings, their impact on concurrency and replication, and related pitfalls such as non‑sequential IDs.

InnoDBauto_incrementconcurrency

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Changes in InnoDB Auto‑Increment Locking Mechanism After MySQL 5.1.22 and Configuration Options