MySQL Indexing Internals and Best Practices

Tue, 25 Aug 2026 00:00:00 +0000

Indexes are the decisive factor for MySQL query performance. Understanding InnoDB’s B+Tree index structure is the only way to write SQL that truly hits indexes.

B+Tree and the Clustered Index

InnoDB organizes indexes with a B+Tree whose non-leaf nodes only store index keys for navigation, while all data lives in leaf nodes that are linked in a doubly-linked list, which is ideal for range scans.

Transactions and Locking

Tue, 25 Aug 2026 00:00:00 +0000

Under concurrency, transactions and locks together guarantee data consistency. InnoDB balances performance and isolation through the coordination of MVCC and locking.

ACID and Isolation Levels

A transaction’s ACID is guaranteed by different mechanisms: atomicity by undo log, durability by redo log, isolation by MVCC and locks, and consistency is the ultimate goal.

The SQL standard defines four isolation levels; InnoDB defaults to REPEATABLE READ:

READ UNCOMMITTED: possible dirty reads
READ COMMITTED: avoids dirty reads, possible non-repeatable reads
REPEATABLE READ: avoids non-repeatable reads (InnoDB additionally avoids phantom reads)
SERIALIZABLE: fully serial, lowest performance

MVCC and Logs

MVCC (Multi-Version Concurrency Control) lets reads avoid locks and reads/writes not block each other. Each row implicitly carries trx_id and roll_pointer, builds historical versions via undo log, and uses a ReadView to decide whether a version is visible to the current transaction.

MySQL on Zhuifeng Notes

MySQL Indexing Internals and Best Practices

B+Tree and the Clustered Index

Transactions and Locking

ACID and Isolation Levels

MVCC and Logs