Consistency in database transactions refers to the requirement that a transaction should only change data from one consistent and valid state to another. More specifically, consistency in database transaction means that any two concurrent transactions should produce identical results regardless of whether they are executed concurrently or in a serial order (Kroenke, et al., 2018). As one of the ACID (Atomicity, consistency, isolation, durability) properties, it is a critical requirement in database design and operation (Microsoft, 2018). These principles were formulated to ensure that a database behaves predictably and reliably (Microsoft, 2018). This helps prevent undesired, partial, or unpredictable modifications to the data, which can disrupt the operation of any application or process that depends on the database. As such, ensuring consistency is critical, especially in large, multi-user databases where concurrent transactions are common.
Consistency can be achieved in two methods: statement-level consistency and transaction-level consistency. In the first case, attempts to modify rows that are currently being processed by other statements will be disallowed; this ensures that the original statement concludes before any others (Kroenke, et al., 2018). With transaction-level consistency, all rows changed by a transaction are protected from changes for the entire duration of the transaction (Kroenke, et al., 2018). Transaction-level consistency, while generally more reliable than statement-level consistency, has certain drawbacks. Firstly, it is resource-intensive and can significantly reduce a database’s throughput (Kroenke, et al., 2018). Secondly, it can cause issues when multiple statements within a transaction affect the same rows (Kroenke, et al., 2018). As such, implementing statement-level consistency requires careful consideration of these drawbacks. Furthermore, before working with database consistency, one needs to verify which method is used in this case and how it affects the database’s use. Nonetheless, consistency in database transactions is crucial for multi-user databases as it ensures that data is changed predictably.
References
Microsoft. (2018). ACID Properties. Windows Dev Center. Web.
Kroenke, D. M., Auer, D. J., Vandenberg, S. L., & Yoder, R. C. (2018). Database Processing: Fundamentals, Design, and Implementation (15th ed.). Pearson.