ACID Properties of a Database: The Keys to Strong Data Consistency
ACID stands for Atomicity, Consistency, Isolation, and Durability. These four ACID properties define database transactions. When they are all met, they guarantee database transaction validity, even in the event of system crashes, power failures, and other errors.
- Atomicity ensures that all operations within a transaction are treated as a single unit, which all succeed or fail together.
- Consistency ensures that a transaction can only bring the database from one valid state to another, allowing only valid data to be written and preventing data corruption. This stability is maintained whether the transaction succeeds or fails.
- Isolation determines how and when changes made by one transaction become visible to others.* If multiple transactions occur at the same time, they will not impact other’s executions. Complete isolation of concurrently running transactions could mean that one transaction cannot perform an insert into a table being queried by another transaction. Therefore, real-world considerations usually require a compromise between perfect transaction isolation and performance.
- Durability ensures that transaction results are permanently stored in the system (such as backups and transaction logs). Modifications must persist even if the system fails or there is a loss of power.
*Serializable and snapshot isolation are the top two isolation levels from a strictness standpoint.
An ACID database or ACID-compliant database upholds the ACID properties of Atomicity, Consistency, Isolation, and Durability.
CAP Theorem (also referred to as CAP) was introduced in 2000 and states that “in the presence of a network partition, there has to be a choice between consistency and 100% availability.”
The term “consistency” in both ACID and CAP can be confusing since it’s used differently in each context. With CAP Theorem, “consistency” is more of a fundamental concept, referring to a guarantee that every participant in a distributed system shares a common understanding of a data element’s value when read. This type of guarantee is often described as strong consistency or linearizability. In fact, it would be better to compare CAP’s version of consistency to the isolation levels in ACID since both deal with the values that read operations are allowed to see.
ACID’s “consistency,” conversely, pertains to the data integrity guarantees ensuring that the entire database transitions from one valid state to another. This transition process strictly adheres to integrity constraints, such as data type adherence, null checks, and relationships among data elements.
Since a single ACID transaction can involve multiple data elements, while CAP’s consistency relates to a single element, ACID transactions provide a stronger guarantee than the consistency described in CAP.
ACID compliance is valuable because these four properties guarantee reliable, consistent, and error-free data. This not only benefits your business but your customers and partners as well. ACID-compliant databases offer the following advantages:
- Zero loss of customer data during system or cloud failures
- No accidental creation of inaccurate or duplicate data
- Total consistency, predictability, and reliability in operations
Maintaining ACID compliance allows businesses to make better, more confident decisions, minimize customer issues caused by data errors, and operate more smoothly.
Emerging in the late 2000s, NoSQL databases were designed—at least in the beginning—as a solution to the challenges around big data, the handling of unstructured data, and the need for overall faster processing. It is quick, uses an ad-hoc approach to organize aforementioned data, and is capable of managing diverse data types.
However, the NoSQL database design forced hard choices between availability and consistency, with availability ultimately winning out since it was felt that these types of workloads could make do with eventual consistency.
This decision to focus on availability compromised the consistency property in ACID, ultimately leading to the relinquishment of atomicity and isolation. Since data volumes were low, vertical scaling seemed to suffice – until recently.
Yes, distributed SQL databases, such as YugabyteDB, combine the benefits of an ACID-compliant, relational (i.e. SQL) database with the advantages of a globally distributed, horizontally scalable, auto-sharded (i.e. NoSQL) database.
What are the 4 ACID properties of a DBMS?
The four ACID properties are Atomicity, Consistency, Isolation, and Durability. These four properties define database transactions. When met, they guarantee database transaction validity, even in the event of a crash, power failure, or other errors.
Why do we need ACID properties?
The four ACID properties—Atomicity, Consistency, Isolation, and Durability—come together to ensure data accuracy and consistency so that applications do not see wrong or stale data. With ACID, all data changes are done as if they are a single unit of operation, producing consistent results, acting in isolation from other operations, and getting permanently stored.
What’s the difference between ACID consistency and CAP Theorem consistency?
CAP Theorem’s consistency ensures all distributed system participants agree on a data element’s value, while ACID’s consistency pertains to data integrity guarantees during database state transitions, offering a stronger guarantee than CAP’s consistency.
What is linearizability?
Linearizability is the strongest consistency model in a distributed system. The term is used interchangeably with the term “strongest consistency.”
What databases use ACID?
Relational databases, including distributed SQL databases, such as MySQL, PostgreSQL, Oracle, and YugabyteDB, use ACID transactions and guarantee database transaction validity.
Is a SQL database ACID?
Traditional SQL databases have strong ACID transactional consistency and ACID guarantees, which are vital for systems of record and systems of engagement. However, horizontal scaling on a traditional SQL database is complex and expensive. Distributed SQL databases solve both issues, combining seamless scalability with strong ACID guarantees.
Is a NoSQL database ACID?
Inherently, no. NoSQL was designed to scale horizontally and did not prioritize providing ACID guarantees. NoSQL databases distribute data across multiple nodes or servers, but those updates occur eventually over time, and all nodes are not updated simultaneously. This approach increases availability and read performance over traditional SQL databases but sacrifices consistency. With NoSQL, data retrieved by an application may not always be consistent or reflect the latest updates made to another node or server.
Is the YugabyteDB database ACID?
Yes, YugabyteDB supports ACID transactions without having to trade-off in terms of scale and resiliency, which is key to any system of record. By using YugabyteDB, developers can achieve low latency, ACID guarantees, familiar interfaces, relational capabilities, horizontal scale, high performance, geographic distribution, and ease of deployment— all in one database system.