What’s the Difference Between MySQL Redo Log and Binlog? (Interview Insight)

1. Different Levels

redo log

is the InnoDB storage‑engine‑level log and only affects InnoDB. It primarily supports transaction commit and crash‑recovery mechanisms. binlog is the MySQL server‑level log and does not depend on a specific storage engine. Any data change executed by the server is typically recorded in binlog.

UPDATE user SET age = 20 WHERE id = 1;

2. Different Functions

redo log

’s core function is to guarantee transaction durability (the D in ACID). It follows Write‑Ahead Logging: when an InnoDB data page has not yet been flushed to disk, the modification is first written to the redo log, allowing the system to redo committed transactions after a crash. binlog ’s core function is data archiving, master‑slave replication, and point‑in‑time recovery. It records the logical SQL change process, making it easy for replicas to replay the master’s operations or to recover data after accidental deletion.

Write Ahead Logging (WAL)

3. Different Recorded Content

redo log

records physical changes, focusing on page‑level modifications. Because it deals with low‑level data, the log size is small and writes are fast. binlog records logical changes, usually the executed SQL statements or row events. This logical representation aligns with business semantics and is convenient for replay in different environments.

4. Different Write Timing and Persistence

redo log

is written in a circular buffer (ring buffer) with a fixed space; when the buffer is full it overwrites old entries. During a transaction, InnoDB first writes modifications to the redo‑log buffer and then flushes it according to a configured policy.

redolog：循环写（Ring Buffer）

binlog

is appended sequentially to log files that grow until a size limit, after which a new file is created. It is usually flushed at transaction commit, preserving a global change record.

写 redo log（prepare 状态）2. 写 binlog 3. redo log 提交（commit）