consistent read
A read operation that uses snapshot information to present query results based on a point in time, regardless of changes performed by other transactions running at the same time. If queried data has been changed by another transaction, the original data is reconstructed based on the contents of the undo log. This technique avoids some of the locking issues that can reduce concurrency by forcing transactions to wait for other transactions to finish.
With the repeatable read isolation level, the snapshot is based on the time when the first read operation is performed. With the read committed isolation level, the snapshot is reset to the time of each consistent read operation.
Consistent read is the default mode in which InnoDB processes SELECT statements in READ COMMITTED and REPEATABLE READ isolation levels. Because a consistent read does not set any locks on the tables it accesses, other sessions are free to modify those tables while a consistent read is being performed on the table.
For technical details about the applicable isolation levels, see , "Consistent Nonlocking Reads".
See also ACID.
See also concurrency.
See also isolation level.
See also locking.
See also MVCC.
See also READ COMMITTED.
See also READ UNCOMMITTED.
See also REPEATABLE READ.
See also SERIALIZABLE.
See also transaction.
See also undo log.