ACID properties are a set of characteristics that ensure that database transactions are processed reliably. The acronym stands for Atomicity, Consistency, Isolation, and Durability. Atomicity ensures that a transaction is treated as a single, indivisible unit of work, and either all of the changes made during the transaction are committed, or none of them are. Consistency ensures that a transaction brings the database from one valid state to another. Isolation ensures that concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially. Durability ensures that once a transaction is committed, its effects are permanent, even in the event of a system failure. Together, these properties ensure data integrity and reliability in a database management system.
ACID Properties in DBMS
Let’s discuss them one by one!
What is Atomicity?
In the context of DBMS, atomicity refers to the property that a transaction is an atomic unit of work, meaning it is indivisible and irreducible. This means that a transaction is executed in its entirety, or not at all. If any part of a transaction fails, the entire transaction is rolled back to its initial state, and the changes made by the transaction are undone.
Atomicity is important because it ensures that a database remains in a consistent state, even in the event of a failure. If a transaction is not atomic, and it is only partially executed, the database could be left in an inconsistent state, with some changes made and others not.
In other words, Atomicity means that a database transaction is a single, indivisible unit of work, that is either completed in its entirety or not at all. This ensures that the database remains in a consistent state, even in the event of failure or system crashes.
What is consistency?
The consistency refers to the property that a transaction brings the database from one valid state to another. This means that a transaction must not violate any integrity constraints or rules that are defined on the database. A consistency constraint defines the business rules that must be satisfied for the data to be considered valid.
For example, a consistency constraint may specify that a customer’s credit limit must not be exceeded when placing an order, or that a product’s price must be greater than zero. If a transaction would violate a consistency constraint, it will be rolled back and the changes made by the transaction will be undone.
Consistency is important because it ensures that the data in the database is accurate, complete and consistent. It makes sure that the integrity of the data is maintained and any invalid data is rejected.
What is Isolation?
In the context of databases, isolation refers to the property that a transaction is executed in isolation from other transactions. This means that the changes made by a transaction are not visible to other transactions until the transaction is committed. In other words, while a transaction is executing, it is as if it is the only transaction in the system.
Isolation is important because it ensures that concurrent transactions do not interfere with each other. Without isolation, multiple transactions could try to update the same data at the same time, leading to conflicts and data inconsistencies.
There are different levels of isolation, each providing a different level of isolation between concurrent transactions. Some of the isolation levels are:
- Read Uncommitted: allows transactions to read data that is currently being modified by other transactions.
- Read Committed: allows transactions to read only committed data, but not the data that is currently being modified by other transactions.
- Repeatable Read: allows transactions to read the same data multiple times, but not see the data that is currently being modified by other transactions.
- Serializable: provides the highest level of isolation, allowing transactions to execute as if they were executing serially, one after the other.
What is Durability?
In databases, durability refers to the property that once a transaction is committed, its effects are permanent and survive any subsequent failures. This means that the changes made by a committed transaction are written to durable storage, such as disk, and are guaranteed to persist, even in the event of a power loss, system crash, or other types of failures.
Durability is important because it ensures that the changes made by a transaction are permanent and will not be lost in the event of a failure. Without durability, a transaction could be committed, but its changes would not be written to disk, and could be lost in the event of a failure.
To achieve durability, databases use various techniques, such as writing data to disk, maintaining transaction logs, and using RAID (redundant array of independent disks) storage.
More to Read
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- 13 Examples of Relational Database
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- 9 Types of Databases
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- Operational Database
- Personal Database
- Graph Databases
- Centralized Database