Intersect is used for AND, i.e.

NewDoubleSeriesStore creates a DoubleSeriesStore.

NewIntSeriesStore creates a IntSeriesStore.

TODO: should add separator, in Prometheus `db.go` it's `const sep = '\xff'`.

Union is used for OR, i.e.

Data is a map using SeriesID as key.

DoubleSeriesStore protects the underlying DoubleSeries with a RWMutex.

Index is a map of inverted index with tag name as key and tag value as term for the inverted index.

IntSeriesStore protects the underlying IntSeries with a RWMutex.

InvertedIndex use Term for tag value postings for a list of sorted series ID TODO: Series ID should use locality sensitive hashing https://en.wikipedia.org/wiki/Locality-sensitive_hashing.

Store is the in memory storage with data and index.

StoreMap protects underlying mem store with a RWMutex.