Returns an estimated size of this relation in bytes.
Returns an estimated size of this relation in bytes. This information is used by the planner to decided when it is safe to broadcast a relation and can be overridden by sources that know the size ahead of time. By default, the system will assume that tables are too large to broadcast. This method will be called multiple times during query planning and thus should not perform expensive operations for each invocation.
Note that it is always better to overestimate size than underestimate, because underestimation could lead to execution plans that are suboptimal (i.e. broadcasting a very large table).
::DeveloperApi:: Represents a collection of tuples with a known schema. Classes that extend BaseRelation must be able to produce the schema of their data in the form of a StructType. Concrete implementation should inherit from one of the descendant
Scanclasses, which define various abstract methods for execution.BaseRelations must also define a equality function that only returns true when the two instances will return the same data. This equality function is used when determining when it is safe to substitute cached results for a given relation.