TODO: support for complex expressions.

returns all columns in aggs and the timestamp column.

returns all columns (+timestamp) in the measure operations.

Inits blocks for aggs on input blkSum.

Inits blocks & records to search based on input blkSum and tRange.

This function raw compute segment stats and will return a map[string]*structs.SegStats, for all the measureOps parameter This function will check for timestamp and so should be used for partially enclosed segments, and unrotated segments.

Search a single SearchQuery and returns which records passes the filter.

a helper struct to keep track of which records & blocks need to be searched.