An apparatus can include a number of memory devices and a memory controller coupled to one or more of the number of memory devices. The memory controller can include a row hammer detector. The memory controller can be configured increment for a first time period a row counter in a first data structure and a refresh counter. The memory controller can be configured to increment for a second time period a row counter in a second data structure and the refresh counter. The memory controller can be configured to determine that a value of the refresh counter exceeds a refresh threshold and responsive to the determination that the value of the refresh counter exceeds the refresh threshold, issue a notification.