Compressed refers to key not SR8. Theoretically, L0 will change rarely
after the load (only when a split/spawn occurs at L1) so the L0 SR8s are
written at actual size rather than full size. If the load is being done
via a reorg or unload/reload, each L0 but the last should be exactly
50% full at the end because the index is loaded left to right.
John Wheeler