What is a dirty read?

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The question asks: What is a dirty read?

Because the list of answer options is missing, I cannot analyze each printed choice individually. What I can do is explain the concept of a dirty read and how it is typically distinguished from other read phenomena in database transactions.

A dirty read occurs when a transaction reads data that another concurrent transaction has written but has not yet committed. In other words, you are seeing uncommitted changes from another transaction. If that other transaction is rolled back, the data you read would be invalid or disappear, making the initial read unreliable.

To clarify why this concept matters, think about transaction isolation levels in databases. A dirty read is disallowed under at least the more conservative isolation levels (for instance, at standard Serializable isolation, dirty reads are prevented) because it can lead to cascading effects if uncommitted data is later rolled back.

If you had options, they would typically include statements like:
- A read of data that has been committed by all transactions. (Clear, safe read.)
- A read of data from a transaction that has not yet committed, which turns out to be rolled back later. (This is a dirty read; it’s problematic.)
- A read that cannot see any changes made by other concurrent transactions. (Represents a non-repeating read or a non-phantom scenario depending on context.)
- A read of data that may or may not reflect other transactions’ changes depending on timing. (Describes phenomena like non-repeatable reads or phantom reads depending on the scenario.)

In short, a dirty read = reading uncommitted, potentially rollback-prone data from another transaction. If you obtain the option list, compare each option to this definition to identify which one precisely matches the dirty-read concept.

CS3200.MERGED.SU-1-2025

What is a dirty read?

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