The redo log buffer is the memory area that holds data to be written to the redo log. Redo log buffer size is defined by the innodb_log_buffer_size configuration option. The redo log buffer is periodically flushed to the log file on disk. A large redo log buffer enables large transactions to run without the need to write redo log to disk before the transactions commit. Thus, if you have transactions that update, insert, or delete many rows, making the log buffer larger saves disk I/O.

The innodb_flush_log_at_trx_commit option controls how the contents of the redo log buffer are written to the log file. The innodb_flush_log_at_timeout option controls redo log flushing frequency.