Package org.apache.drill.exec.physical.impl.scan.v3.schema

Class AbstractSchemaTracker

java.lang.Object
org.apache.drill.exec.physical.impl.scan.v3.schema.AbstractSchemaTracker
All Implemented Interfaces:
ScanSchemaTracker
Direct Known Subclasses:
ProjectionSchemaTracker, SchemaBasedTracker
public abstract class AbstractSchemaTracker extends Object implements ScanSchemaTracker
Base class for the projection-based and defined-schema-based scan schema trackers.

  • Field Details

  • Constructor Details

  • Method Details

    • validateProjection

      protected static void validateProjection(TupleMetadata projection, TupleMetadata schema)
      Validate a projection list against a defined-schema tuple. Recursively walks the tree of maps to validate all nested tuples.
      Parameters:
      projection - the parsed projection list
      schema - the defined schema to validate against

    • projectionType

      public ScanSchemaTracker.ProjectionType projectionType()
      Specified by:
      projectionType in interface ScanSchemaTracker

    • errorContext

      public CustomErrorContext errorContext()
      Description copied from interface: ScanSchemaTracker
      The scan-level error context used for errors which may occur before the first reader starts. The reader will provide a more detailed error context that describes what is being read.
      Specified by:
      errorContext in interface ScanSchemaTracker
      Returns:
      the scan-level error context

    • internalSchema

      public MutableTupleSchema internalSchema()
      Description copied from interface: ScanSchemaTracker
      Returns the internal scan schema. Primarily for testing.
      Specified by:
      internalSchema in interface ScanSchemaTracker
      Returns:
      the internal mutable scan schema

    • isResolved

      public boolean isResolved()
      Description copied from interface: ScanSchemaTracker
      Is the scan schema resolved? The schema is resolved depending on the complex lifecycle explained in the class comment. Resolution occurs when the wildcard (if any) is expanded, and all explicit projection columns obtain a definite type. If schema change is disabled, the schema will not change once it is resolved. If schema change is allowed, then batches or readers may extend the schema, triggering a schema change, and so the scan schema may move from one resolved state to another.

      The schema will be fully resolved after the first batch of data arrives from a reader (since the reader lifecycle will then fill in any missing columns.) The schema may be resolved sooner (such as if a strict provided schema, or an early reader schema is available and there are no missing columns.)

      Specified by:
      isResolved in interface ScanSchemaTracker
      Returns:
      if the schema is resolved, and hence the ScanSchemaTracker.outputSchema() is available, false if the schema contains one or more dynamic columns which are not yet resolved.

    • schemaVersion

      public int schemaVersion()
      Description copied from interface: ScanSchemaTracker
      Gives the output schema version which will start at some arbitrary positive number.

      If schema change is allowed, the schema version allows detecting schema changes as the scan schema moves from one resolved state to the next. Each schema will have a unique, increasing version number. A schema change has occurred if the version is newer than the previous output schema version.

      Specified by:
      schemaVersion in interface ScanSchemaTracker
      Returns:
      the schema version. The absolute number is not important, rather an increase indicates one or more columns were added at the top level or within a map at some nesting level

    • checkResolved

      protected void checkResolved()
      Determine if the schema is resolved. It is resolved if the schema itself is resolved. Since an empty schema is resolved, for the SELECT * case, we require at least one column, which means that something (provided schema, early reader schema) has provided us with a schema. Once resolved, a schema can never become unresolved: readers are not allowed to add dynamic columns.

    • applyImplicitCols

      public TupleMetadata applyImplicitCols()
      Description copied from interface: ScanSchemaTracker
      Indicate that implicit column parsing is complete. Returns the implicit columns as identified by the implicit column handler, in the order of the projection list. Implicit columns do not appear in a reader input schema, and it is an error for the reader to produce such columns.
      Specified by:
      applyImplicitCols in interface ScanSchemaTracker
      Returns:
      a sub-schema of only implicit columns, in the order in which they appear in the output schema

    • readerInputSchema

      public TupleMetadata readerInputSchema()
      Description copied from interface: ScanSchemaTracker
      The schema which the reader should produce. Depending on the type of the scan (specifically, if #isProjectAll() is true), the reader may produce additional columns beyond those in the the reader input schema. However, for any batch, the reader, plus the missing columns handler, must produce all columns in the reader input schema.

      Formally:

      
 reader input schema = output schema - implicit col schema
      Specified by:
      readerInputSchema in interface ScanSchemaTracker
      Returns:
      the sub-schema which includes those columns which the reader should provide, excluding implicit columns

    • missingColumns

      public TupleMetadata missingColumns(TupleMetadata readerOutputSchema)
      Description copied from interface: ScanSchemaTracker
      Identifies the missing columns given a reader output schema. The reader output schema are those columns which the reader actually produced.

      Formally:

      
 missing cols = reader input schema - reader output schema

      The reader output schema can contain extra, newly discovered columns. Those are ignored when computing missing columns. Thus, the subtraction is set subtraction: remove columns common to the two sets.

      Specified by:
      missingColumns in interface ScanSchemaTracker

    • resolveMissingCols

      public void resolveMissingCols(TupleMetadata missingCols)
      Description copied from interface: ScanSchemaTracker
      The missing column handler obtains the list of missing columns from #missingColumns(). Depending on the scan lifecycle, some of the columns may have a type, others may be dynamic. The missing column handler chooses a type for any dynamic columns, then calls this method to tell the scan schema tracker the now-resolved column type.

      Note: a goal of the provided/defined schema system is to avoid the need to guess types for missing columns since doing so quite often leads to problems further downstream in the query. Ideally, the type of missing columns will be known (via the provided or defined schema) to avoid such conflicts.

      Specified by:
      resolveMissingCols in interface ScanSchemaTracker

    • outputSchema

      public TupleMetadata outputSchema()
      Description copied from interface: ScanSchemaTracker
      Returns the scan output schema which is a somewhat complicated computation that depends on the projection type.

      For a wildcard schema:

      
 output schema = implicit cols U reader output schema

      For an explicit projection:

      
 output schema = projection list
      Where the projection list is augmented by types from the provided schema, implicit columns or readers.

      A defined schema is the output schema, so:

       output schema = defined schema
      Specified by:
      outputSchema in interface ScanSchemaTracker
      Returns:
      the complete output schema provided by the scan to downstream operators. Includes both reader and implicit columns, in the order of the projection list or, for a wildcard, in the order of the first reader