this introduces disk format v4
now the summary rows for a term are stored in their own
"dictionary row" format, previously the same information
was stored in special term frequency rows
this now allows us to easily iterate all the terms for a field
in sorted order (useful for many other fuzzy data structures)
at the top-level of bleve you can now browse terms within a field
using the following api on the Index interface:
FieldDict(field string) (index.FieldDict, error)
FieldDictRange(field string, startTerm []byte, endTerm []byte) (index.FieldDict, error)
FieldDictPrefix(field string, termPrefix []byte) (index.FieldDict, error)
fixes#127
now can track array positions for field values
stored fields now include this in the key
and the back index now uses protobufs to simplify serialization
closes#73
ultimately this is make it more convenient for us to wire up
different elements of the analysis pipeline, without having to
preload everything into memory before we need it
separately the index layer now has a mechanism for storing
internal key/value pairs. this is expected to be used to
store the mapping, and possibly other pieces of data by the
top layer, but not exposed to the user at the top.
previously we used the format:
't' <utf-8 term> <byte separator> <16-bit field id> <utf-8 docID> <byte separator>
now we have moved the field before the term, resulting in:
't' <16-bit field id> <utf-8 term> <byte separator> <utf-8 docID> <byte separator>
this means now instead of all fields with the same term being grouped together
all terms within the same field are grouped together
this allows us to enumerate the terms used with a field
this allows us to implement prefix search, and possibly improve numeric range queries
