Dirty Reads and Phantoms

Dirty Read occurs when a user reads data that has not been commited yet, uncommited data. An example would be when Person A is working on a transaction and makes some changes but does not commit the data and looks at another transaction. Meanwhile Person B comes to look at the same data that person A just made some changes to. Person B is looking at the data, the uncommited data, before the changes were made, causing a dirty read to occur.

Phantom Read happens when data seems to have mysteriously appeared. Data getting changed in current transaction by other transactions is called Phantom Reads. New rows can be added by other transactions, so you get different number of rows by firing same query in current transaction.