Pushes down variant field access information to the data source.

Implementations should validate if the variant accesses can be pushed down based on the data source's capabilities. If some accesses cannot be pushed down, the implementation can choose to:

• Push down only the supported accesses and return true
• Reject all pushdown and return false

The implementation should store the variant access information that can be pushed down. The stored information will be retrieved later via #pushedVariantAccess().

Returns the variant access information that has been pushed down to this scan.

This method is called by the optimizer after #pushVariantAccess to retrieve what variant accesses were actually accepted by the data source. The optimizer uses this information to rewrite the query plan.

If #pushVariantAccess was not called or returned false, this should return an empty array.

Returns the actual schema of this data source scan, which may be different from the physical schema of the underlying storage, as column pruning or other optimizations may happen.

Subclasses can implement this method to indicate if the support for columnar data should be determined by each partition or is set as a default for the whole scan.

A description string of this scan, which may includes information like: what filters are configured for this scan, what's the value of some important options like path, etc. The description doesn't need to include #readSchema(), as Spark already knows it.

By default this returns the class name of the implementation. Please override it to provide a meaningful description.

Returns an array of custom metrics which are collected with values at the driver side only. Note that these metrics must be included in the supported custom metrics reported by supportedCustomMetrics.

Returns an array of supported custom metrics with name and description. By default it returns empty array.

Returns the physical representation of this scan for batch query. By default this method throws exception, data sources must overwrite this method to provide an implementation, if the Table that creates this scan returns TableCapability#BATCH_READ support in its Table#capabilities().

If the scan supports runtime filtering and implements SupportsRuntimeFiltering, this method may be called multiple times. Therefore, implementations can cache some state to avoid planning the job twice.

Returns the physical representation of this scan for streaming query with continuous mode. By default this method throws exception, data sources must overwrite this method to provide an implementation, if the Table that creates this scan returns TableCapability#CONTINUOUS_READ support in its Table#capabilities().

Returns the physical representation of this scan for streaming query with micro-batch mode. By default this method throws exception, data sources must overwrite this method to provide an implementation, if the Table that creates this scan returns TableCapability#MICRO_BATCH_READ support in its Table#capabilities().