See Also ACID, concurrency, isolation level, locking, transaction. 

## locking read 

 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 . 

SELECT ... FOR SHARE  replaces SELECT ... LOCK IN SHARE MODE  in MySQL 8.0.1, but LOCK IN SHARE MODE  remains available for backward compatibility. 

See Section 15.7.2.4, “Locking Reads” . See Also deadlock, isolation level, locking, non-locking read, read-only transaction. 

## log 

 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. 

## log buffer 

 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. 

See Also log file, redo log. 

## log file 

 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. 

See Also ib_logfile, log buffer, redo log. 

## log group 

 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. 

## logical 

 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. 

## logical backup 

 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. 

## 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 

