In addition to constructing a new dictionary structure for each block and
eliminating the expensive sorting step, SPIMI has a third important component:
compression. Both the postings and the dictionary terms can be stored
compactly on disk if we employ compression. Compression increases the ef-
ficiency of the algorithm further because we can process even larger blocks,
and because the individual blocks require less space on disk. We refer readers
to the literature for this aspect of the algorithm (Section 4.7).
The time complexity of SPIMI is Θ(T) because no sorting of tokens is required
and all operations are at most linear in the size of the collection.