1. A method for storing write records in a hierarchical index comprising: maintaining a hierarchical index in a computer-readable memory, wherein the hierarchical index comprises a root node and one or more stem nodes corresponding to respective data location ranges of a data file; accessing a write command identifying a data location range of the data file; adding, responsive to the write command, one or more write records for the write command as one or more respective leaf nodes to the hierarchical index maintained in the computer-readable memory, wherein each leaf node is attached to a stem node whose data location range encompasses the data location range of the write command; and conditionally growing the hierarchical index based on a number of leaf nodes attached to a given stem node in the hierarchical index.