Internal Structure of InnoDB Redo Log in MySQL 5.7: MTR Lifecycle and Mutex-Based Operation Principles

This document explains the internal operation of the WAL (Write-Ahead Log) based Redo Log, which ensures transaction integrity and durability in MySQL InnoDB. Specifically, it defines the structure (mtr_t) and lifecycle (start, commit, release_resource) of the MTR (Mini-Transaction), the smallest unit of Redo Log operations, and discusses how a single user transaction is split into multiple MTRs for data changes, Undo, and commit information to optimize parallel processing and performance. It also states that in MySQL 5.7, a Mutex-based operation is applied where log_sys_mutex is acquired when passing session-specific MTR information to the Global Redo Log Buffer to prevent concurrency conflicts. Finally, it summarizes the entire flow from when Dirty Pages are added to the Buffer Pool's Flush List until they are flushed to disk.