Interview Questions
1. What is Row versioning?
Microsoft introduced row versioning as an alternative to shared locks in SQL Server 2005. With row versioning, rows are read into tempdb at the beginning of a transaction and the transaction uses that copy of those rows throughout the duration of the transaction. Row versioning protects the transaction from
- Dirty reads
- Nonrepeatable reads
- Phantoms
Even when row versioning is used, SQL Server still takes an exclusive lock on a row before updating it.
Row versioning allows for optimum concurrency (multiple users accessing data at the same time), while providing good
protection.
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