The ACID model is a set of database design principles that emphasize aspects of reliability that are important for business data and mission-critical applications. MySQL includes components such as the InnoDB
storage engine that adhere closely to the ACID model so that data is not corrupted and results are not distorted by exceptional conditions such as software crashes and hardware malfunctions. When you rely on ACID-compliant features, you do not need to reinvent the wheel of consistency checking and crash recovery mechanisms. In cases where you have additional software safeguards, ultra-reliable hardware, or an application that can tolerate a small amount of data loss or inconsistency, you can adjust MySQL settings to trade some of the ACID reliability for greater performance or throughput.
The following sections discuss how MySQL features, in particular the InnoDB
storage engine, interact with the categories of the ACID model:
A: atomicity.
C: consistency.
I:: isolation.
D: durability.
The atomicity aspect of the ACID model mainly involves InnoDB
transactions. Related MySQL features include:
The autocommit
setting.
The COMMIT
statement.
The ROLLBACK
statement.
The consistency aspect of the ACID model mainly involves internal InnoDB
processing to protect data from crashes. Related MySQL features include:
The InnoDB
doublewrite buffer. See Section 15.6.4, “Doublewrite Buffer”.
InnoDB
crash recovery. See InnoDB Crash Recovery.
The isolation aspect of the ACID model mainly involves InnoDB
transactions, in particular the isolation level that applies to each transaction. Related MySQL features include:
The autocommit
setting.
Transaction isolation levels and the SET TRANSACTION
statement. See Section 15.7.2.1, “Transaction Isolation Levels”.
The low-level details of InnoDB
locking. Details can be viewed in the INFORMATION_SCHEMA
tables (see Section 15.15.2, “InnoDB INFORMATION_SCHEMA Transaction and Locking Information”) and Performance Schema data_locks
and data_lock_waits
tables.
The durability aspect of the ACID model involves MySQL software features interacting with your particular hardware configuration. Because of the many possibilities depending on the capabilities of your CPU, network, and storage devices, this aspect is the most complicated to provide concrete guidelines for. (And those guidelines might take the form of “buy new hardware”.) Related MySQL features include:
The InnoDB
doublewrite buffer. See Section 15.6.4, “Doublewrite Buffer”.
The innodb_flush_log_at_trx_commit
variable.
The sync_binlog
variable.
The innodb_file_per_table
variable.
The write buffer in a storage device, such as a disk drive, SSD, or RAID array.
A battery-backed cache in a storage device.
The operating system used to run MySQL, in particular its support for the fsync()
system call.
An uninterruptible power supply (UPS) protecting the electrical power to all computer servers and storage devices that run MySQL servers and store MySQL data.
Your backup strategy, such as frequency and types of backups, and backup retention periods.
For distributed or hosted data applications, the particular characteristics of the data centers where the hardware for the MySQL servers is located, and network connections between the data centers.