Read Path Flow

This package contains the structures and functions for read plans.

Read Path Planning flow:

Read Execution:

OraScanBuilder:

• responsible for setting up an OraScan
• for an OracleTable with optional filter pushdowns and requiredSchema it sets up a OraPlan, that is passed to the OraScan.
  • it is not required for the OraPlan to apply all filters, as these are applied on top of the org.apache.spark.sql.execution.datasources.v2.DataSourceV2ScanRelation Ensuring these can be pushed to Oracle will be done in the Oracle pushdown rules.

OraScan :

• acts like a FileScan, so the org.apache.spark.sql.execution.datasources.PruneFileSourcePartitions rule can apply on this scan, and partition and data filter expressions can be pushed to it.
• but implementation behavior is completely overridden.
• it has an empty fileIndex
• it reports partitionFilters and dataFilters to be empty. The filters pushed into the OraPlan are reapplied on top of the org.apache.spark.sql.execution.datasources.v2.DataSourceV2ScanRelation
• For physical planning:
  • it uses OraQuerySplitting to infer how to parallelize the OraPlan
  • each OracleDBSplit has an enhanced OraPlan.
  • An OraPartition is setup for each Split with its oracle query, bind values and preferred locations.
• stats estimation: try to use a table's stats otherwise estimate as unknown