From Wikipedia (which has great and detailed examples for this): A non-repeatable read occurs, when during the course of a transaction, a row is retrieved twice and the values within the row differ between reads. and A phantom read occurs when, in the course of a transaction, two identical queries are executed, and the collection … Read more
This isolation level allows dirty reads. One transaction may see uncommitted changes made by some other transaction. To maintain the highest level of isolation, a DBMS usually acquires locks on data, which may result in a loss of concurrency and a high locking overhead. This isolation level relaxes this property. You may want to check … Read more
Read committed is an isolation level that guarantees that any data read was committed at the moment is read. It simply restricts the reader from seeing any intermediate, uncommitted, ‘dirty’ read. It makes no promise whatsoever that if the transaction re-issues the read, will find the Same data, data is free to change after it … Read more