Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for encoding and decoding delta values. In one aspect, a method includes accessing a compression buffer having a start position, a sentinel position, and a data storage region; obtaining a first value; determining that a second value stored in the sentinel position does not match a first sentinel value; determining that a third value stored in the start position matches a second sentinel value; and storing the first value at the start position of the compression buffer.