In-memory database system

An in-memory database system stores an entirety of a database within main memory of the computer system. The database includes a table comprising a plurality of rows including a particular row. A first transaction updating the particular row is executed to create a first version of the particular row. A second transaction updating the particular row is executed to create a second version of the particular row. The first version is visible only to the first transaction, and the second version is visible only to the second transaction. The in-memory database system may associate an index with the database table, the index referencing the plurality of rows, including referencing the first version of the particular row and the second version of the particular row. The in-memory database system may initiate garbage collection of the first version of the particular row and/or the second version of the particular row.