What are phantom reads in database transactions?

What are phantom reads in database transactions?

Phantom reads occur when a transaction reads a set of rows that match a certain condition, but another transaction inserts or deletes rows that affect that condition before the first transaction is completed.

Can you give me an example of a phantom read?

Sure! Imagine Transaction A reads all records of customers with a balance greater than $100. Meanwhile, Transaction B inserts a new customer with a balance of $150. If Transaction A reads again before it commits, it will see this new record, which is a phantom read.

How can phantom reads be prevented?

Phantom reads can be prevented by using higher isolation levels like Serializable, which ensures that no other transactions can insert or delete rows that would affect the results of the current transaction.

Are there any downsides to using Serializable isolation?

Yes, using Serializable isolation can lead to decreased concurrency and performance, as it locks more data and can cause transactions to wait longer.