Major Description
We have added the PATCHED norms sub format in lucene 50, which uses a bitset to mark documents that have the most common value (when >97% of the documents have that value). This works well for fields that have a predominant value length, and then a small number of docs with some other random values. But another common case is having a handful of very common value lengths, like with a title field.
We can use a table (see TABLE_COMPRESSION) to store the most common values, and save an oridinal for the "other" case, at which point we can lookup in the secondary patch table.