A computer system includes a memory and a processor coupled to the memory. The processor is configured to execute instructions that cause execution of an in-memory database system that includes one or more database tables. Each database table includes a plurality of rows, where data representing each row is stored in the memory. The in-memory database system also includes a plurality of indexes associated with the one or more database tables, where each index is implemented by a lock-free data structure. Update logic at the in-memory database system is configured to update a first version of a particular row to create a second version of the particular row. The in-memory database system includes a non-blocking garbage collector configured to identify data representing outdated versions of rows.