Small utility to get statistics on stored (string and binary) fields in a Lucene index.

Usage:
ro.deathy.fieldsizes.Runner <luceneIndexDir> [statsFile]

Stats generated are of two kinds:

* Uses/Appearances of stored fields:

Columns:
- Field Name: Name of field
- Document Appearances: Number of times a field appears in a document. This can be more than total number of documents in case the field appears more than once in documents.
- Percentage: Percentage of Document Appearances compared to number of documents in index.

* Bytes usage of stored fields:

Columns:
- Field Name: Name of field
- Bytes Used: Total number of bytes used by this field across the whole index
- Percentage: Bytes Used for field as percentage of total number of Bytes Used values for all fields in index.

Bytes usage is calculated for stored String value fields and binary value stored fields.
For string values, bytes is taken as bytes needed to store that value in UTF-8