Adaptive radix external in-place radix sort

Systems and methods for sorting a data set stored on an external device. A plurality of smaller radix sizes are determined, based on a first radix size and performance characteristics of an external data storage device, whose sizes add up to a first radix size for an in-place radix sort. The smaller radix sizes reduce a total time to perform the in-place radix sort. Each level of a multiple level in-place radix sort is performed with the smaller radix sizes. Each level of the sort includes dividing the data set into N buckets; dividing the buffer into N buckets; and iteratively loading a respective segment in each bucket of the data set into a respective bucket of the buffer, performing an in-place radix sort on the data in the buffer, and returning sorted buffer data to the data set on the external storage device.