The redo log is a disk-based data structure used during crash recovery to correct data written by incomplete transactions. During normal operations, the redo log encodes requests to change table data that result from SQL statements or low-level API calls. Modifications that did not finish updating the data files before an unexpected shutdown are replayed automatically during initialization, and before connections are accepted. For information about the role of the redo log in crash recovery, see Section 14.19.2, “InnoDB Recovery”.
By default, the redo log is physically represented on disk by two
ib_logfile1. MySQL writes to the redo log
files in a circular fashion. Data in the redo log is encoded in
terms of records affected; this data is collectively referred to
as redo. The passage of data through the redo log is represented
by an ever-increasing LSN value.
Information and procedures related to redo logs are described under the following topics in the section:
To change the number or the size of your
log files, perform the following steps:
Stop the MySQL server and make sure that it shuts down without errors.
my.cnfto change the log file configuration. To change the log file size, configure
innodb_log_file_size. To increase the number of log files, configure
Start the MySQL server again.
InnoDB detects that the
from the redo log file size, it writes a log checkpoint, closes
and removes the old log files, creates new log files at the
requested size, and opens the new log files.