The first time through, startNumFields should be 0, where there ought
to be more optimization assuming later docs have similar fields as the
first doc.
-VisitableDocValueFields API for persisted DV field list
-making dv configs overridable at field level
-enabling on the fly/runtime un inverting of doc values
-few UT updates
inserted to the list of dv enabled fields list -
DocValueFields in mem segment.
Moved back to the original type `DocValueFields map[uint16]bool`
for easy look up to check whether the fieldID is
configured for dv storage.
+ Track memory usage at a segment level
+ Add a new scorch API: MemoryUsed()
- Aggregate the memory consumption across
segments when API is invoked.
+ TODO:
- Revisit the second iteration if it can be gotten
rid off, and the size accounted for during the first
run while building an in-mem segment.
- Accounting for pointer and slice overhead.
docValues are persisted along with the index,
in a columnar fashion per field with variable
sized chunking for quick look up.
-naive chunk level caching is added per field
-data part inside a chunk is snappy compressed
-metaHeader inside the chunk index the dv values
inside the uncompressed data part
-all the fields are docValue persisted in this iteration
