Examples with UnionColumnState org.apache.drill.exec.physical.resultSet.impl.UnionState.UnionColumnState used on opensource projects

Example 1 with UnionColumnState

use of org.apache.drill.exec.physical.resultSet.impl.UnionState.UnionColumnState in project drill by apache.

the class ColumnBuilder method buildSimpleList.

/**
 * Create a list that is promised to only ever contain a single type (at least
 * during this write session). The list acts as a repeated vector in which each
 * element can be null. The writer is presented as an array of the single type.
 * <p>
 * List vectors (lists of optional values) are not supported in
 * Drill. The code here works up through the scan operator. But, other operators do
 * not support the {@code ListVector</tt> type.
 *
 * @param parent the parent (tuple, union or list) that holds this list
 * @param columnSchema metadata description of the list which must contain
 * exactly one subtype
 * @return the column state for the list
 */
private ColumnState buildSimpleList(ContainerState parent, ColumnMetadata columnSchema) {
    // The variant must have the one and only type.
    assert columnSchema.variantSchema().size() == 1;
    assert columnSchema.variantSchema().isSimple();
    // Create the manager for the one and only column within the list.
    final ListState listState = new ListState(parent.loader(), parent.vectorCache().childCache(columnSchema.name()));
    // Create the child vector, writer and state.
    final ColumnMetadata memberSchema = columnSchema.variantSchema().listSubtype();
    final ColumnState memberState = buildColumn(listState, memberSchema);
    listState.setSubColumn(memberState);
    // Create the list vector. Contains a single type.
    final ListVector listVector = new ListVector(columnSchema.schema().cloneEmpty(), parent.loader().allocator(), null);
    listVector.setChildVector(memberState.vector());
    // Create the list writer: an array of the one type.
    final ListWriterImpl listWriter = new ListWriterImpl(columnSchema, listVector, memberState.writer());
    final AbstractObjectWriter listObjWriter = new ArrayObjectWriter(listWriter);
    // Create the list vector state that tracks the list vector lifecycle.
    final ListVectorState vectorState = new ListVectorState(listWriter, memberState.writer().events(), listVector);
    // Assemble it all into a union column state.
    return new UnionColumnState(parent.loader(), listObjWriter, vectorState, listState);
}

Example 2 with UnionColumnState

use of org.apache.drill.exec.physical.resultSet.impl.UnionState.UnionColumnState in project drill by apache.

the class ColumnBuilder method buildUnionList.

/**
 * Create a list based on a (possible) union. The list starts empty here. The client
 * can then add types as they are discovered. The list itself will transition from a
 * list of nulls (no child type), to a list of a single type, to a list of unions.
 * The writer interface will consistently present the list as a list of unions, even
 * when the list itself has no subtype or a single subtype.
 * <p>
 * List vectors (lists of unions) are not supported in
 * Drill. The code here works up through the scan operator. But, other operators do
 * not support the {@code ListVector} type.
 *
 * @param parent the parent (tuple, union or list) that holds this list
 * @param columnSchema description of the list (must be empty of
 * subtypes)
 * @return the column state for the list
 */
private ColumnState buildUnionList(ContainerState parent, ColumnMetadata columnSchema) {
    // The variant must start out empty.
    assert columnSchema.variantSchema().size() == 0;
    // Create the union writer, bound to an empty list shim.
    final UnionWriterImpl unionWriter = new UnionWriterImpl(columnSchema);
    unionWriter.bindShim(new EmptyListShim());
    final VariantObjectWriter unionObjWriter = new VariantObjectWriter(unionWriter);
    // Create the list vector. Starts with the default (dummy) data
    // vector which corresponds to the empty union shim above.
    // Don't get the list vector from the vector cache. List vectors may
    // have content that varies from batch to batch. Only the leaf
    // vectors can be cached.
    final ListVector listVector = new ListVector(columnSchema.schema(), parent.loader().allocator(), null);
    // Create the list vector state that tracks the list vector lifecycle.
    final ListVectorState vectorState = new ListVectorState(unionWriter, listVector);
    // Create the list writer: an array of unions.
    final AbstractObjectWriter listWriter = new ArrayObjectWriter(new ListWriterImpl(columnSchema, listVector, unionObjWriter));
    // Create the manager for the columns within the list (which may or
    // may not be grouped into a union.)
    final ListState listState = new ListState(parent.loader(), parent.vectorCache().childCache(columnSchema.name()));
    // Bind the union state to the union writer to handle column additions.
    unionWriter.bindListener(listState);
    // Assemble it all into a union column state.
    return new UnionColumnState(parent.loader(), listWriter, vectorState, listState);
}

Example 3 with UnionColumnState

use of org.apache.drill.exec.physical.resultSet.impl.UnionState.UnionColumnState in project drill by apache.

the class ColumnBuilder method buildUnion.

/**
 * Builds a union column.
 * <p>
 * The union vector type is not well supported in Drill. The idea is that
 * arbitrary operators can absorb schema changes by converting vectors to
 * unions so that an operator can handle, say, a nullable int and a varchar.
 * In practice, most operators don't support this feature. (Sort does -- but
 * does not manage memory for the union case.) In principal, union can't solve
 * the problem because ODBC and JDBC don't support unions, and it is easy
 * to envision changes that unions won't solve (int and varchar types combining
 * in a join column, say.) Still, Drill supports unions, so the code here
 * does so. Unions are fully tested in the row set writer mechanism.
 *
 * @param parent container of vectors
 * @param columnSchema implied projection type for the column
 * @return column
 */
private ColumnState buildUnion(ContainerState parent, ColumnMetadata columnSchema) {
    assert columnSchema.isVariant() && !columnSchema.isArray();
    // vectors can be cached.
    assert columnSchema.variantSchema().size() == 0;
    final UnionVector vector = new UnionVector(columnSchema.schema(), parent.loader().allocator(), null);
    // Then the union writer.
    final UnionWriterImpl unionWriter = new UnionWriterImpl(columnSchema, vector, null);
    final VariantObjectWriter writer = new VariantObjectWriter(unionWriter);
    // The union vector state which manages the types vector.
    final UnionVectorState vectorState = new UnionVectorState(vector, unionWriter);
    // Create the manager for the columns within the union.
    final UnionState unionState = new UnionState(parent.loader(), parent.vectorCache().childCache(columnSchema.name()));
    // Bind the union state to the union writer to handle column additions.
    unionWriter.bindListener(unionState);
    // Assemble it all into a union column state.
    return new UnionColumnState(parent.loader(), writer, vectorState, unionState);
}