Package org.apache.drill.exec.physical.resultSet

Interface ResultSetLoader

All Known Implementing Classes:
ResultSetLoaderImpl
public interface ResultSetLoader
Builds a result set (series of zero or more row sets) based on a defined schema which may evolve (expand) over time. Automatically rolls "overflow" rows over when a batch fills.

Many of the methods in this interface verify that the loader is in the proper state. For example, an exception is thrown if the caller attempts to save a row before starting a batch. However, the per-column write methods are checked only through assertions that should enabled during testing, but will be disabled during production.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    DEFAULT_ROW_COUNT
     

  • Method Summary

    Modifier and Type
    Method
    Description
    TupleMetadata
    activeSchema()
    Returns the active output schema; the schema used by the writers, minus any unprojected columns.
    boolean
    atLimit()
    After a harvest(), call, call this method to determine if the scan limit has been hit.
    int
    batchCount()
    Total number of batches created.
    void
    close()
    Called after all rows are returned, whether because no more data is available, or the caller wishes to cancel the current row batch and complete.
    CustomErrorContext
    errorContext()
    Context for error messages.
    VectorContainer
    harvest()
    Harvest the current row batch, and reset the mutator to the start of the next row batch (which may already contain an overflow row.
    boolean
    hasRows()
    Report whether the loader currently holds rows.
    boolean
    isProjectionEmpty()
    Reports if this is an empty projection such as occurs in a SELECT COUNT(*) query.
    int
    maxBatchSize()
    The maximum number of rows for the present batch.
    VectorContainer
    outputContainer()
    Returns the output container which holds (or will hold) batches from this loader.
    TupleMetadata
    outputSchema()
    The schema of the harvested batch.
    int
    schemaVersion()
    Current schema version.
    ResultSetLoader
    setRow(Object... values)
    Load a row using column values passed as variable-length arguments.
    void
    setTargetRowCount(int count)
    Adjust the number of rows to produce in the next batch.
    int
    skipRows(int requestedCount)
    Requests to skip the given number of rows.
    boolean
    startBatch()
    Start a new row batch.
    int
    targetRowCount()
    The number of rows produced by this loader (as configured in the loader options.)
    int
    targetVectorSize()
    The largest vector size produced by this loader (as specified by the value vector limit.)
    long
    totalRowCount()
    Total number of rows loaded for all previous batches and the current batch.
    ResultVectorCache
    vectorCache()
    Peek at the internal vector cache for readers that need a bit of help resolving types based on what was previously seen.
    boolean
    writeable()
    Reports whether the loader is in a writable state.
    RowSetLoader
    writer()
    Writer for the top-level tuple (the entire row).

  • Field Details

  • Method Details

    • errorContext

      CustomErrorContext errorContext()
      Context for error messages.

    • schemaVersion

      int schemaVersion()
      Current schema version. The version increments by one each time a column is added.
      Returns:
      the current schema version

    • setTargetRowCount

      void setTargetRowCount(int count)
      Adjust the number of rows to produce in the next batch. Takes affect after the next call to startBatch().
      Parameters:
      count - target batch row count

    • targetRowCount

      int targetRowCount()
      The number of rows produced by this loader (as configured in the loader options.)
      Returns:
      the target row count for batches that this loader produces

    • maxBatchSize

      int maxBatchSize()
      The maximum number of rows for the present batch. Will be the lesser of the
      invalid @link 
      {@link #targetRowCount()) and the overall scan limit remaining.

    • targetVectorSize

      int targetVectorSize()
      The largest vector size produced by this loader (as specified by the value vector limit.)
      Returns:
      the largest vector size. Attempting to extend a vector beyond this limit causes automatic vector overflow and terminates the in-flight batch, even if the batch has not yet reached the target row count

    • batchCount

      int batchCount()
      Total number of batches created. Includes the current batch if the row count in this batch is non-zero.
      Returns:
      the number of batches produced including the current one

    • totalRowCount

      long totalRowCount()
      Total number of rows loaded for all previous batches and the current batch.
      Returns:
      total row count

    • hasRows

      boolean hasRows()
      Report whether the loader currently holds rows. If within a batch, reports if at least one row has been read (which might be a look-ahead row.) If between batches, reports if a look-ahead row is available.
      Returns:
      true if at least one row is available to harvest, false otherwise

    • startBatch

      boolean startBatch()
      Start a new row batch. Valid only when first started, or after the previous batch has been harvested.
      Returns:
      true if another batch can be read, false if the reader has reached the given scan limit.

    • writer

      RowSetLoader writer()
      Writer for the top-level tuple (the entire row). Valid only when the mutator is actively writing a batch (after startBatch() but before harvest().)
      Returns:
      writer for the top-level columns

    • writeable

      boolean writeable()
      Reports whether the loader is in a writable state. The writable state occurs only when a batch has been started, and before that batch becomes full.
      Returns:
      true if the client can add a row to the loader, false if not

    • setRow

      ResultSetLoader setRow(Object... values)
      Load a row using column values passed as variable-length arguments. Expects map values to represented as an array. A schema of (a:int, b:map(c:varchar)) would be> set as
      loadRow(10, new Object[] {"foo"});
      Values of arrays can be expressed as a Java array. A schema of (a:int, b:int[]) can be set as
      loadRow(10, new int[] {100, 200});
      . Primarily for testing, too slow for production code.

      If the row consists of a single map or list, then the one value will be an Object array, creating an ambiguity. Use writer().set(0, value); in this case.

      Parameters:
      values - column values in column index order
      Returns:
      this loader

    • skipRows

      int skipRows(int requestedCount)
      Requests to skip the given number of rows. Returns the number of rows actually skipped (which is limited by batch count.)

      Used in SELECT COUNT(*) style queries when the downstream operators want just record count, but no actual rows.

      Also used to fill in a batch of only null values (such a filling in a set of null vectors for unprojected columns.)

      Parameters:
      requestedCount - the number of rows to skip
      Returns:
      the actual number of rows skipped, which may be less than the requested amount. If less, the client should call this method for multiple batches until the requested count is reached

    • isProjectionEmpty

      boolean isProjectionEmpty()
      Reports if this is an empty projection such as occurs in a SELECT COUNT(*) query. If the projection is empty, then the downstream needs only the row count set in each batch, but no actual vectors will be created. In this case, the client can do the work to populate rows (the data will be discarded), or can call skipRows(int) to skip over the number of rows that would have been read if any data had been projected.

      Note that the empty schema case can also occur if the project list from the SELECT clause is disjoint from the table schema. For example, SELECT a, b from a table with schema (c, d).

      Returns:
      true if no columns are actually projected, false if at least one column is projected

    • activeSchema

      TupleMetadata activeSchema()
      Returns the active output schema; the schema used by the writers, minus any unprojected columns. This is usually the same as the output schema, but may differ if the writer adds columns during an overflow row. Unlike the output schema, this schema is defined as long as the loader is open.

    • outputContainer

      VectorContainer outputContainer()
      Returns the output container which holds (or will hold) batches from this loader. For use when the container is needed prior to "harvesting" a batch. The data is not valid until harvest() is called, and is no longer valid once startBatch() is called.
      Returns:
      container used to publish results from this loader

    • harvest

      VectorContainer harvest()
      Harvest the current row batch, and reset the mutator to the start of the next row batch (which may already contain an overflow row.

      The schema of the returned container is defined as:

      • The schema as passed in via the loader options, plus
      • Columns added dynamically during write, minus
      • Any columns not included in the project list, minus
      • Any columns added in the overflow row.
      That is, column order is as defined by the initial schema and column additions. In particular, the schema order is not defined by the projection list. (Another mechanism is required to reorder columns for the actual projection.)
      Returns:
      the row batch to send downstream

    • atLimit

      boolean atLimit()
      After a harvest(), call, call this method to determine if the scan limit has been hit. If so, treat this as the final batch for the reader, even if more data is available to read.
      Returns:
      true if the scan has reached a set scan row limit, false if there is no limit, or more rows can be read.

    • outputSchema

      TupleMetadata outputSchema()
      The schema of the harvested batch. Valid until the start of the next batch.
      Returns:
      the extended schema of the harvested batch which includes any allocation hints used when creating the batch

    • vectorCache

      ResultVectorCache vectorCache()
      Peek at the internal vector cache for readers that need a bit of help resolving types based on what was previously seen.
      Returns:
      real or dummy vector cache

    • close

      void close()
      Called after all rows are returned, whether because no more data is available, or the caller wishes to cancel the current row batch and complete.