See Also ACID, concurrency, isolation level, locking, transaction. locking read log log buffer log file log group logical logical backup loose_  A prefix added to  InnoDB  configuration options after server  startup , so any new configuration options not recognized by the current level of MySQL do not cause a startup failure. MySQL processes configuration options  A  backup  that reproduces table structure and data, without copying the actual data files. For example, the mysqldump  command produces a logical backup, because its output contains statements such as  CREATE TABLE  and  INSERT  that can re-create the data. Contrast with  physical backup . A logical backup offers flexibility (for example, you could edit table definitions or insert statements before restoring), but can take substantially longer to  restore  than a physical backup. See Also backup, mysqldump, physical backup, restore.  A type of operation that involves high-level, abstract aspects such as tables, queries, indexes, and other SQL concepts. Typically, logical aspects are important to make database administration and application development convenient and usable. Contrast with  physical . See Also logical backup, physical.  The set of files that make up the  redo log , typically named  ib_logfile0  and  ib_logfile1 . (For that reason, sometimes referred to collectively as  ib_logfile .) See Also ib_logfile, redo log.  One of the  ib_logfile N  files that make up the  redo log . Data is written to these files from the  log buffer  memory area.  The memory area that holds data to be written to the  log files  that make up the  redo log . It is controlled by the innodb_log_buffer_size  configuration option.  In the  InnoDB  context, “log”  or “log files”  typically refers to the  redo log  represented by the  ib_logfile N  files. Another type of  InnoDB  log is the  undo log , which is a storage area that holds copies of data modified by active transactions. Other kinds of logs that are important in MySQL are the  error log  (for diagnosing startup and runtime problems), binary log  (for working with replication and performing point-in-time restores), the  general query log  (for diagnosing application problems), and the  slow query log  (for diagnosing performance problems). See Also binary log, error log, general query log, ib_logfile, redo log, slow query log, undo log. See Section 15.7.2.4, “Locking Reads” . See Also deadlock, isolation level, locking, non-locking read, read-only transaction. SELECT ... FOR SHARE  replaces  SELECT ... LOCK IN SHARE MODE  in MySQL 8.0.1, but  LOCK IN SHARE MODE  remains available for backward compatibility.  A  SELECT  statement that also performs a  locking  operation on an  InnoDB  table. Either  SELECT ... FOR UPDATE  or  SELECT ... LOCK IN SHARE MODE . It has the potential to produce a  deadlock , depending on the isolation level  of the transaction. The opposite of a  non-locking read . Not allowed for global tables in a  read- only transaction . See Also log file, redo log. See Also ib_logfile, log buffer, redo log. 6165