Interview Q&A / SQL & DBMS

1. What are dirty reads, non-repeatable reads and phantom reads?

   A dirty read sees another transaction's uncommitted data. A non-repeatable read gets a different value for the same row on a second read. A phantom read gets a different set of rows for the same query.

   IntermediateQuick answer1 min read
2. What is the difference between optimistic and pessimistic locking?

   Pessimistic locking locks the row up front so others must wait, assuming conflicts are likely. Optimistic locking takes no lock and checks at update time, usually with a version number, whether someone else changed the row.

   IntermediateQuick answer1 min read