Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for storing data on in a storage medium. In one aspect, a method includes receiving a key-value pair including a key k and a value v. The method further includes encoding the key-value pair as (i) a first key-value pair including a first key k1 and first value v1, and (ii) a second key-value pair including a second key k2. The method further includes inserting the first key-value pair and the second key-value pair in a trie.