Foreword

The ACD characteristics (atomicity, consistency, and durability) of transactions are guaranteed by the undo log and redo log. The redo log is not recorded until the transaction commits, but after the begin begins.

redo log

redo log: redo log, used to record changes in transaction operations to ensure transaction durability.The redo log starts recording after the transaction starts, regardless of whether the transaction is committed or not, it will be recorded. When an exception occurs (such as a power failure during data persistence), InnoDB will use the redo log to restore to the moment before the power failure to ensure data integrity.completeness.

The default value of innodb_log_buffer_size is 16M, which is the size of the redo log buffer. It starts to write the redo
log as the transaction starts. If the transaction is relatively large, in order to avoid spending too much disk IO during transaction execution, it can be setA relatively large redo log cache saves disk IO.
InnoDB modifies the operation data, not directly modifies the data on the disk, but actually modifies the data in the Buffer Pool.InnoDB always records the data changes in the Buffer Pool to the redo log first for data recovery after a crash.First record the redo log, and then slowly flush the dirty data in the Buffer Pool to the disk.

Two files in the directory specified by innodb_log_group_home_dir: ib_logfile0, ib_logfile1, which are called redo logs.

buffer pool:
Function: Accelerate reading and writing, directly operate the data page, and write redo log modification is completed, there is a special thread to write the dirty page in the buffer
pool to disk.