Definition

Read skew is an anomaly where a transaction reads outdated data in one table or column while reading updated related data in another, leading to inconsistency across reads within the same transaction.

Core concept

It happens when isolation level doesn’t enforce strict ordering of reads.

Use cases

Eliminated by higher isolation (repeatable read or serializable).

Example

In a bank DB, one transaction reads old balance but new transaction count in same transaction, leading to internal inconsistency.

References

Known anomaly (less common term).