In MySQL 5.6 and higher, the syntax  FLUSH TABLES ... FOR EXPORT  writes some data to disk for  InnoDB tables that make it simpler to back up those tables by copying the data files. See Also backup, flush, InnoDB, shutdown.  A tree data structure used for spatial indexing of multi-dimensional data such as geographical coordinates, rectangles or polygons. See Also B-tree. R R-tree RAID random dive raw backup READ COMMITTED read phenomena READ UNCOMMITTED  Acronym for “Redundant Array of Inexpensive Drives” . Spreading I/O operations across multiple drives enables greater  concurrency  at the hardware level, and improves the efficiency of low-level write operations that otherwise would be performed in sequence. See Also concurrency.  A technique for quickly estimating the number of different values in a column (the column’s  cardinality ).  InnoDB samples pages at random from the index and uses that data to estimate the number of different values. See Also cardinality.  The initial set of backup files produced by the  MySQL Enterprise Backup  product, before the changes reflected in the  binary log  and any  incremental backups  are applied. At this stage, the files are not ready to  restore . After these changes are applied, the files are known as a  prepared backup . See Also binary log, hot backup, ibbackup_logfile, incremental backup, MySQL Enterprise Backup, prepared backup, restore.  An  isolation level  that uses a  locking  strategy that relaxes some of the protection between  transactions , in the interest of performance. Transactions cannot see uncommitted data from other transactions, but they can see data that is committed by another transaction after the current transaction started. Thus, a transaction never sees any bad data, but the data that it does see may depend to some extent on the timing of other transactions. When a transaction with this isolation level performs  UPDATE ... WHERE  or  DELETE ... WHERE  operations, other transactions might have to wait. The transaction can perform  SELECT ... FOR UPDATE , and  LOCK IN SHARE MODE  operations without making other transactions wait. 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 Also ACID, isolation level, locking, REPEATABLE READ, SERIALIZABLE, transaction.  Phenomena such as  dirty reads ,  non-repeatable reads , and  phantom  reads which can occur when a transaction reads data that another transaction has modified. See Also dirty read, non-repeatable read, phantom.  The  isolation level  that provides the least amount of protection between transactions. Queries employ a locking  strategy that allows them to proceed in situations where they would normally wait for another transaction. However, this extra performance comes at the cost of less reliable results, including data that has been changed by other transactions and not committed yet (known as  dirty read ). Use this isolation level with great caution, and be aware that the results might not be consistent or reproducible, depending on what other transactions are doing 6179