Class MergeScanRowSource

java.lang.Object
org.apache.derby.impl.store.access.sort.Scan
org.apache.derby.impl.store.access.sort.SortScan
org.apache.derby.impl.store.access.sort.MergeScan
org.apache.derby.impl.store.access.sort.MergeScanRowSource
All Implemented Interfaces:
ScanControllerRowSource, ScanManager, GenericScanController, GroupFetchScanController, RowCountable, RowLocationRetRowSource, RowSource, ScanController, ScanInfo
public class MergeScanRowSource extends MergeScan implements ScanControllerRowSource
Wrapping the output of a MergeScan in a RowSource for the benefit of the createAndLoadConglomerate and loadConglomerate interface. The output of a MergeScan is written to a file when we need more than one level of merge runs. MergeScan implements ScanController, this class just implements the RowSource interface.

  • Constructor Details

  • Method Details

    • next

      public boolean next() throws StandardException
      Description copied from class: MergeScan
      Move to the next position in the scan.
      Specified by:
      next in interface GroupFetchScanController
      Specified by:
      next in interface ScanController
      Overrides:
      next in class MergeScan
      Returns:
      True if there is a next position in the scan, false if there isn't.
      Throws:
      StandardException - Standard exception policy.
      See Also:

    • getNextRowFromRowSource

      public DataValueDescriptor[] getNextRowFromRowSource() throws StandardException
      Description copied from interface: RowSource
      Get the next row as an array of column objects. The column objects can be a JBMS Storable or any Serializable/Externalizable/Formattable/Streaming type.
      A return of null indicates that the complete set of rows has been read.

      A null column can be specified by leaving the object null, or indicated by returning a non-null getValidColumns. On streaming columns, it can be indicated by returning a non-null get FieldStates.

      If RowSource.needToClone() is true then the returned row (the DataValueDescriptor[]) is guaranteed not to be modified by drainer of the RowSource (except that the input stream will be read, of course) and drainer will keep no reference to it before making the subsequent nextRow call. So it is safe to return the same DataValueDescriptor[] in subsequent nextRow calls if that is desirable for performance reasons.

      If RowSource.needToClone() is false then the returned row (the DataValueDescriptor[]) may be be modified by drainer of the RowSource, and the drainer may keep a reference to it after making the subsequent nextRow call. In this case the client should severe all references to the row after returning it from getNextRowFromRowSource().

      Specified by:
      getNextRowFromRowSource in interface RowSource
      Throws:
      StandardException - Standard Derby Error Policy

    • needsRowLocation

      public boolean needsRowLocation()
      Description copied from interface: RowLocationRetRowSource
      needsRowLocation returns true iff this the row source expects the drainer of the row source to call rowLocation after getting a row from getNextRowFromRowSource.
      Specified by:
      needsRowLocation in interface RowLocationRetRowSource
      Returns:
      true iff this row source expects some row location to be returned
      See Also:

    • needsRowLocationForDeferredCheckConstraints

      public boolean needsRowLocationForDeferredCheckConstraints()
      Specified by:
      needsRowLocationForDeferredCheckConstraints in interface RowLocationRetRowSource

    • needsToClone

      public boolean needsToClone()
      Description copied from interface: RowSource
      Does the caller of getNextRowFromRowSource() need to clone the row in order to keep a reference to the row past the getNextRowFromRowSource() call which returned the row. This call must always return the same for all rows in a RowSource (ie. the caller will call this once per scan from a RowSource and assume the behavior is true for all rows in the RowSource).
      Specified by:
      needsToClone in interface RowSource
      See Also:

    • rowLocation

      public void rowLocation(RowLocation rl)
      Description copied from interface: RowLocationRetRowSource
      rowLocation is a callback for the drainer of the row source to return the rowLocation of the current row, i.e, the row that is being returned by getNextRowFromRowSource. This interface is for the purpose of loading a base table with index. In that case, the indices can be built at the same time the base table is laid down once the row location of the base row is known. This is an example pseudo code on how this call is expected to be used: 
      boolean needsRL = rowSource.needsRowLocation();
DataValueDescriptor[] row;
while((row = rowSource.getNextRowFromRowSource()) != null)
{
        RowLocation rl = heapConglomerate.insertRow(row);
        if (needsRL)
                rowSource.rowLocation(rl);
}

      NeedsRowLocation and rowLocation will ONLY be called by a drainer of the row source which CAN return a row location. Drainer of row source which cannot return rowLocation will guarantee to not call either callbacks. Conversely, if NeedsRowLocation is called and it returns true, then for every row return by getNextRowFromRowSource, a rowLocation callback must also be issued with the row location of the row. Implementor of both the source and the drain of the row source must be aware of this protocol.
      The RowLocation object is own by the caller of rowLocation, in other words, the drainer of the RowSource. This is so that we don't need to new a row location for every row. If the Row Source wants to keep the row location, it needs to clone it (RowLocation is a ClonableObject).
      Specified by:
      rowLocation in interface RowLocationRetRowSource
      See Also:

    • offendingRowLocation

      public void offendingRowLocation(RowLocation rl, long containdId) throws StandardException
      Specified by:
      offendingRowLocation in interface RowLocationRetRowSource
      Throws:
      StandardException

    • getValidColumns

      public FormatableBitSet getValidColumns()
      All columns are always set from a sorter
      Specified by:
      getValidColumns in interface RowSource

    • closeRowSource

      public void closeRowSource()
      Close the row source - implemented by MergeScan already
      Specified by:
      closeRowSource in interface RowSource