Example apparatus, methods, data structures, and computers control indexing to facilitate duplicate determinations. One example method includes indexing, in a global index, a unique chunk processed by a data de-duplicator. Indexing the unique chunk in the global index can include updating an expedited data structure associated with the global index. The example method can also include selectively indexing, in a temporal index, a relationship chunk processed by the data de-duplicator. The relationship chunk is a chunk that is related to another chunk processed by the data de-duplicator by sequence, storage location, and/or similarity hash value. Indexing the relationship chunk in the temporal index can also include updating one or more expedited data structures associated with the temporal index. The expedited data structures and indexes can then be consulted to resolve a duplicate determination being made by a data reducer.