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

Class SchemaNegotiatorImpl

java.lang.Object

org.apache.drill.exec.physical.impl.scan.v3.lifecycle.SchemaNegotiatorImpl

All Implemented Interfaces:

SchemaNegotiator

Direct Known Subclasses:

FileSchemaNegotiatorImpl

public class SchemaNegotiatorImpl
extends Object
implements SchemaNegotiator

Implementation of the schema negotiation between scan operator and batch reader. Anticipates that the select list (and/or the list of predefined fields (implicit, partition) might be set by the scanner. For now, all readers have their own implementation of the select set.

Handles both early- and late-schema readers. Early-schema readers provide a table schema, late-schema readers do not.

If the reader (or, later, the scanner) has a SELECT list, then that select list is pushed down into the result set loader created for the reader.

Also handles parsing out various column types, filling in null columns and (via the vector cache), minimizing changes across readers. In the worst case, a reader might have a column "c" in one file, might skip "c" in the second file, and "c" may appear again in a third file. This negotiator, along with the scan projection and vector cache, "smoothes out" schema changes by preserving the vector for "c" across all three files. In the first and third files "c" is a vector written by the reader, in the second, it is a null column filled in by the scan projector (assuming, of course, that "c" is nullable or an array.)

Pushes limits into the result set loader. The caller must either check the return value from {#code startBatch()}, or call atLimit() after harvest() to detect when the scan has reached the limit. Treat the limit condition the same as EOF.

Field Summary

Fields

Modifier and Type	Field	Description
protected CustomErrorContext	baseErrorContext
protected int	batchSize
protected boolean	isSchemaComplete
protected CustomErrorContext	readerErrorContext
protected final ReaderLifecycle	readerLifecycle
protected TupleMetadata	readerSchema

Constructor Summary

Constructors

Constructor	Description
SchemaNegotiatorImpl(ReaderLifecycle readerLifecycle)

Method Summary

Modifier and Type	Method	Description
void	batchSize(int maxRecordsPerBatch)	Set the preferred batch size (which may be overridden by the result set loader in order to limit vector or batch size.)
ResultSetLoader	build()	Callback from the schema negotiator to build the schema from information from both the table and scan operator.
OperatorContext	context()
CustomErrorContext	errorContext()	Returns the error context to use for this reader: either the parent or the reader-specific context set in SchemaNegotiator.setErrorContext(CustomErrorContext).
StaticBatchBuilder	implicitColumnsLoader()
TupleMetadata	inputSchema()	Returns the reader input schema: the schema which describes the set of columns this reader should produce.
boolean	isProjectionEmpty()	Report whether the projection list is empty, as occurs in two cases: SELECT COUNT(*) ... -- empty project. SELECT a, b FROM table(c d) -- disjoint project.
boolean	isSchemaComplete()
ManagedReader	newReader(ReaderFactory<?> readerFactory)
protected void	onEndBatch()
CustomErrorContext	parentErrorContext()	The context to use as a parent when creating a custom context.
ProjectedColumn	projectionFor(String colName)
TupleMetadata	providedSchema()	Returns the provided schema, if defined.
void	schemaIsComplete(boolean isComplete)
void	setErrorContext(CustomErrorContext errorContext)	Specify an advanced error context which allows the reader to fill in custom context values.
void	tableSchema(TupleMetadata schema)
void	tableSchema(TupleMetadata schema, boolean isComplete)	Specify the table schema if this is an early-schema reader.
String	userName()	Name of the user running the query.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

readerLifecycle

protected final ReaderLifecycle readerLifecycle

readerSchema

protected TupleMetadata readerSchema

isSchemaComplete

protected boolean isSchemaComplete

batchSize

protected int batchSize

baseErrorContext

protected CustomErrorContext baseErrorContext

readerErrorContext

protected CustomErrorContext readerErrorContext

Constructor Details

SchemaNegotiatorImpl

public SchemaNegotiatorImpl(ReaderLifecycle readerLifecycle)

Method Details

isProjectionEmpty

public boolean isProjectionEmpty()

Description copied from interface: SchemaNegotiator

Report whether the projection list is empty, as occurs in two cases:

• SELECT COUNT(*) ... -- empty project.

SELECT a, b FROM table(c d) -- disjoint project.