org.apache.drill.exec.physical.resultSet.model.hyper

Class HyperReaderBuilder

java.lang.Object

org.apache.drill.exec.physical.resultSet.model.ReaderBuilder

org.apache.drill.exec.physical.resultSet.model.hyper.HyperReaderBuilder

public class HyperReaderBuilder
extends ReaderBuilder

Base reader builder for a hyper-batch. The semantics of hyper-batches are a bit rough. When a single batch, we can walk the vector tree to get the information we need. But, hyper vector wrappers don't provide that same information, so we can't just walk them. Further, the code that builds hyper-batches appears perfectly happy to accept batches with differing schemas, something that will cause the readers to blow up because they must commit to a particular kind of reader for each vector.

The solution is to build the readers in two passes. The first builds a metadata model for each batch and merges those models. (This version requires strict identity in schemas; a fancier solution could handle, say, the addition of map members in one batch vs. another or the addition of union/list members across batches.)

The metadata (by design) has the information we need, so in the second pass we walk the metadata hierarchy and build up readers from that, creating vector accessors as we go to provide a runtime path from the root vectors (selected by the SV4) to the inner vectors (which are not represented as hypervectors.)

The hypervector wrapper mechanism provides a crude way to handle inner vectors, but it is awkward, and does not lend itself to the kind of caching we'd like for performance, so we use our own accessors for inner vectors. The outermost hyper vector accessors wrap a hyper vector wrapper. Inner accessors directly navigate at the vector level (from a vector provided by the outer vector accessor.)

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	HyperReaderBuilder.HyperVectorAccessor Vector accessor used by the column accessors to obtain the vector for each column value.

Method Summary

Modifier and Type	Method and Description
static RowSetReaderImpl	build(BatchAccessor batch) Build a hyper-batch reader given a batch accessor.
static RowSetReaderImpl	build(VectorContainer container, TupleMetadata schema, SelectionVector4 sv4)
protected List<AbstractObjectReader>	buildContainerChildren(VectorContainer container)
protected List<AbstractObjectReader>	buildContainerChildren(VectorContainer container, TupleMetadata schema)
protected List<AbstractObjectReader>	buildMapMembers(VectorAccessor va, TupleMetadata mapSchema)
protected AbstractObjectReader	buildVectorReader(VectorAccessor va, ColumnMetadata metadata)

Methods inherited from class org.apache.drill.exec.physical.resultSet.model.ReaderBuilder

buildReader, buildScalarReader

Methods inherited from class java.lang.Object

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

Method Detail

build

public static RowSetReaderImpl build(VectorContainer container,
                                     TupleMetadata schema,
                                     SelectionVector4 sv4)

build

public static RowSetReaderImpl build(BatchAccessor batch)
                              throws SchemaChangeException

Build a hyper-batch reader given a batch accessor.

Parameters:

batch - wrapper which provides the container and SV4

Returns:

a row set reader for the hyper-batch

Throws:

SchemaChangeException - if the individual batches have inconsistent schemas (say, a column in batch 1 is an INT, but in batch 2 it is a VARCHAR)

buildContainerChildren

protected List<AbstractObjectReader> buildContainerChildren(VectorContainer container)
                                                     throws SchemaChangeException

Throws:

SchemaChangeException

buildContainerChildren

protected List<AbstractObjectReader> buildContainerChildren(VectorContainer container,
                                                            TupleMetadata schema)

buildVectorReader

protected AbstractObjectReader buildVectorReader(VectorAccessor va,
                                                 ColumnMetadata metadata)

buildMapMembers

protected List<AbstractObjectReader> buildMapMembers(VectorAccessor va,
                                                     TupleMetadata mapSchema)