Index compression is good, especially for random access
Stefan Büttcher, Charles L. A. Clarke · 2007
Index compression techniques are known to substantially decrease the storage requirements of a text retrieval system. As a side-effect, they may increase its retrieval performance by reducing disk I/O overhead. Despite this advantage, developers sometimes choose to store index data in uncompressed form, in order to not obstruct random access into each index term's postings list.