Explore the intricacies of the mysqldump command and its options, including –master-data, –single-transaction, and –result-file, to ensure consistent and reliable backups in MySQL database administration.
Table of Contents
Question
Examine this command, which executes successfully: shell> mysqldump –master-data=2 –single-transaction –result-file=dump.sql mydb
Which two statements are true? (Choose two.)
A. It executes flush tables with read lock.
B. It enforces consistent backups for all storage engines.
C. The backup created is a consistent data dump.
D. This option uses the READ COMMITTED transaction isolation mode.
E. It is a cold backup.
Answer
C. The backup created is a consistent data dump.
E. It is a cold backup.
Explanation
The mysqldump command with the specified options creates a consistent data dump, which is a logical backup of the database. Here’s a breakdown of the options and their implications:
–master-data=2: This option includes the binary log file name and position in the dump file, allowing for point-in-time recovery or replication setup. The value 2 specifies that the binary log coordinates should be written as a CHANGE MASTER comment in the dump file.
–single-transaction: This option ensures that all tables are read from a consistent state by executing a global READ LOCK and maintaining a transaction snapshot. This guarantees a consistent backup, even for InnoDB tables, by avoiding inconsistencies caused by concurrent data modifications during the backup process.
–result-file=dump.sql: This option specifies the output file where the SQL statements for recreating the database structure and data will be written.
With these options, the mysqldump command creates a consistent data dump (C) by acquiring a global read lock, which effectively blocks any concurrent data modifications, and reads the data from a consistent snapshot. This process is known as a cold backup (E) because it requires locking the database, making it unavailable for writes during the backup operation.
Option A is incorrect because the command does not explicitly execute FLUSH TABLES WITH READ LOCK. The –single-transaction option implicitly acquires a global read lock, but the command itself does not include the FLUSH TABLES WITH READ LOCK statement.
Option B is also incorrect because the –single-transaction option enforces consistent backups for InnoDB and other transactional storage engines, but it may not guarantee consistent backups for non-transactional storage engines like MyISAM.
Option D is incorrect because the –single-transaction option does not explicitly use the READ COMMITTED transaction isolation mode. Instead, it creates a consistent snapshot by acquiring a global read lock.
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