Because we do not know how large the postings list of a term will be when
we first encounter it, we allocate space for a short postings list initially and
double the space each time it is full (lines 8–9). This means that some memory
is wasted, which counteracts the memory savings from the omission of
termIDs in intermediate data structures. However, the overall memory requirements
for the dynamically constructed index of a block in SPIMI are
still lower than in BSBI.