Editing Isolation (database systems) (section)

===Repeatable reads===
In this isolation level, a lock-based [[concurrency control]] DBMS implementation keeps read and write locks (acquired on selected data) until the end of the transaction.  However, ''range-locks'' are not managed, so '''''[[#Phantom reads|phantom reads]]''''' can occur.

Write skew is possible at this isolation level in some systems. Write skew is a phenomenon where two writes are allowed to the same column(s) in a table by two different writers (who have previously read the columns they are updating), resulting in the column having data that is a mix of the two transactions.<ref>{{cite web|url=https://vladmihalcea.com/2015/10/20/a-beginners-guide-to-read-and-write-skew-phenomena/|title=A beginner's guide to read and write skew phenomena|author=Vlad Mihalcea|date=2015-10-20}}</ref><ref>{{cite web|url=https://wiki.postgresql.org/wiki/SSI#Simple_Write_Skew|title=Postgresql wiki - SSI}}</ref>