java.lang.Object
org.apache.derby.impl.store.access.sort.Scan
All Implemented Interfaces:
ScanManager, GenericScanController, GroupFetchScanController, RowCountable, ScanController, ScanInfo
Direct Known Subclasses:
SortBufferRowSource, SortScan

public abstract class Scan extends Object implements ScanManager, ScanInfo
Abstract base class for all sort classes which return rows from the sort. Subclasses must implement fetch, next, and close.
  • Constructor Details

    • Scan

      public Scan()
  • Method Details

    • didNotQualify

      public void didNotQualify() throws StandardException
      A call to allow client to indicate that current row does not qualify.

      Indicates to the ScanController that the current row does not qualify for the scan. If the isolation level of the scan allows, this may result in the scan releasing the lock on this row.

      Note that some scan implimentations may not support releasing locks on non-qualifying rows, or may delay releasing the lock until sometime later in the scan (ie. it may be necessary to keep the lock until either the scan is repositioned on the next row or page).

      This call should only be made while the scan is positioned on a current valid row.

      This call does not make sense for sort scans.

      Specified by:
      didNotQualify in interface ScanController
      Throws:
      StandardException - Standard exception policy.
    • fetchNextGroup

      public int fetchNextGroup(DataValueDescriptor[][] row_array, RowLocation[] rowloc_array) throws StandardException
      Fetch the next N rows from the table.

      Currently unimplemented for sorts.

      Specified by:
      fetchNextGroup in interface GroupFetchScanController
      Parameters:
      row_array - The array of rows to copy rows into. row_array[].length must >= 1. The first entry must be non-null destination rows, other entries may be null and will be allocated by access if needed.
      rowloc_array - If non-null, the array of row locations to copy into. If null, no row locations are retrieved.
      Returns:
      The number of qualifying rows found and copied into the provided array of rows. If 0 then the scan is complete, otherwise the return value will be: 1 <= row_count <= row_array.length
      Throws:
      StandardException - Standard exception policy.
    • fetchNextGroup

      public int fetchNextGroup(DataValueDescriptor[][] row_array, RowLocation[] old_rowloc_array, RowLocation[] new_rowloc_array) throws StandardException
      Specified by:
      fetchNextGroup in interface GroupFetchScanController
      Throws:
      StandardException
    • fetchSet

      public void fetchSet(long max_rowcnt, int[] key_column_numbers, BackingStoreHashtable hash_table) throws StandardException
      Insert all rows that qualify for the current scan into the input Hash table.

      Currently unimplemented for sorts.

      Specified by:
      fetchSet in interface ScanManager
      Parameters:
      max_rowcnt - The maximum number of rows to insert into the Hash table. Pass in -1 if there is no maximum.
      key_column_numbers - The column numbers of the columns in the scan result row to be the key to the Hashtable. "0" is the first column in the scan result row (which may be different than the first row in the table of the scan).
      Throws:
      StandardException - Standard exception policy.
    • doesCurrentPositionQualify

      public boolean doesCurrentPositionQualify() throws StandardException
      Returns true if the current position of the scan still qualifies under the set of qualifiers passed to the openScan().
      Specified by:
      doesCurrentPositionQualify in interface ScanController
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • fetchLocation

      public void fetchLocation(RowLocation templateLocation) throws StandardException
      Fetch the location of the current position in the scan.
      Specified by:
      fetchLocation in interface ScanController
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • getScanInfo

      public ScanInfo getScanInfo() throws StandardException
      Return ScanInfo object which describes performance of scan.

      Return ScanInfo object which contains information about the current scan.

      Currently the ScanInfo does not have any performance data.

      Specified by:
      getScanInfo in interface GenericScanController
      Returns:
      The ScanInfo object which contains info about current scan.
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • getEstimatedRowCount

      public long getEstimatedRowCount() throws StandardException
      Get the total estimated number of rows in the container.

      The number is a rough estimate and may be grossly off. In general the server will cache the row count and then occasionally write the count unlogged to a backing store. If the system happens to shutdown before the store gets a chance to update the row count it may wander from reality.

      This call is currently only supported on Heap conglomerates, it will throw an exception if called on btree conglomerates.

      Specified by:
      getEstimatedRowCount in interface RowCountable
      Returns:
      The total estimated number of rows in the conglomerate.
      Throws:
      StandardException - Standard exception policy.
    • setEstimatedRowCount

      public void setEstimatedRowCount(long count) throws StandardException
      Set the total estimated number of rows in the container.

      Often, after a scan, the client of RawStore has a much better estimate of the number of rows in the container than what store has. For instance if we implement some sort of update statistics command, or just after a create index a complete scan will have been done of the table. In this case this interface allows the client to set the estimated row count for the container, and store will use that number for all future references.

      This call is currently only supported on Heap conglomerates, it will throw an exception if called on btree conglomerates.

      Specified by:
      setEstimatedRowCount in interface RowCountable
      Parameters:
      count - the estimated number of rows in the container.
      Throws:
      StandardException - Standard exception policy.
    • isCurrentPositionDeleted

      public boolean isCurrentPositionDeleted() throws StandardException
      Returns true if the current position of the scan is at a deleted row.
      Specified by:
      isCurrentPositionDeleted in interface ScanController
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • isKeyed

      public boolean isKeyed()
      Return whether this is a keyed conglomerate.

      Specified by:
      isKeyed in interface GenericScanController
      Returns:
      whether this is a keyed conglomerate.
    • isTableLocked

      public boolean isTableLocked()
      Return whether this scan is table locked.
      Specified by:
      isTableLocked in interface GenericScanController
      Returns:
      whether this is table locked.
    • delete

      public boolean delete() throws StandardException
      Delete the row at the current position of the scan.
      Specified by:
      delete in interface ScanController
      Returns:
      true if the delete was successful, false if the current position is no longer valid (ie. if it was already deleted).
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • reopenScan

      public void reopenScan(DataValueDescriptor[] startKeyValue, int startSearchOperator, Qualifier[][] qualifier, DataValueDescriptor[] stopKeyValue, int stopSearchOperator) throws StandardException
      Reposition the current scan.
      Specified by:
      reopenScan in interface GenericScanController
      Parameters:
      startKeyValue - An indexable row which holds a (partial) key value which, in combination with the startSearchOperator, defines the starting position of the scan. If null, the starting position of the scan is the first row of the conglomerate.
      startSearchOperator - an operator which defines how the startKeyValue is to be searched for. If startSearchOperator is ScanController.GE, the scan starts on the first row which is greater than or equal to the startKeyValue. If startSearchOperation is ScanController.GT, the scan starts on the first row whose key is greater than startKeyValue. The startSearchOperation parameter is ignored if the startKeyValue parameter is null.
      qualifier - An array of qualifiers which, applied to each key, restrict the rows returned by the scan. Rows for which any one of the qualifiers returns false are not returned by the scan. If null, all rows are returned.
      stopKeyValue - An indexable row which holds a (partial) key value which, in combination with the stopSearchOperator, defines the ending position of the scan. If null, the ending position of the scan is the last row of the conglomerate.
      stopSearchOperator - an operator which defines how the stopKeyValue is used to determine the scan stopping position. If stopSearchOperation is ScanController.GE, the scan stops just before the first row which is greater than or equal to the stopKeyValue. If stopSearchOperation is ScanController.GT, the scan stops just before the first row whose key is greater than startKeyValue. The stopSearchOperation parameter is ignored if the stopKeyValue parameter is null.
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • reopenScanByRowLocation

      public void reopenScanByRowLocation(RowLocation startRowLocation, Qualifier[][] qualifier) throws StandardException
      Reposition the current scan. This call is semantically the same as if the current scan had been closed and a openScan() had been called instead. The scan is reopened against the same conglomerate, and the scan is reopened with the same "scan column list", "hold" and "forUpdate" parameters passed in the original openScan.
      Specified by:
      reopenScanByRowLocation in interface GenericScanController
      Parameters:
      startRowLocation - An existing RowLocation within the conglomerate, at which to position the start of the scan. The scan will begin at this location and continue forward until the end of the conglomerate. Positioning at a non-existent RowLocation (ie. an invalid one or one that had been deleted), will result in an exception being thrown when the first next operation is attempted.
      qualifier - An array of qualifiers which, applied to each key, restrict the rows returned by the scan. Rows for which any one of the qualifiers returns false are not returned by the scan. If null, all rows are returned.
      Throws:
      StandardException - Standard exception policy.
    • replace

      public boolean replace(DataValueDescriptor[] val, FormatableBitSet validColumns) throws StandardException
      Replace the entire row at the current position of the scan.
      Specified by:
      replace in interface ScanController
      Returns:
      true if the replace was successful, false if the current position is no longer valid (ie. if it was deleted).
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • newRowLocationTemplate

      public RowLocation newRowLocationTemplate() throws StandardException
      Return a row location object of the correct type to be used in calls to fetchLocation.
      Specified by:
      newRowLocationTemplate in interface GenericScanController
      Returns:
      a row location object to be used in calls to fetchLocation.
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • positionAtRowLocation

      public boolean positionAtRowLocation(RowLocation rl) throws StandardException
      Description copied from interface: ScanController
      Positions the scan at row location and locks the row. If the scan is not opened, it will be reopened if this is a holdable scan and there has not been any operations which causes RowLocations to be invalidated.
      Specified by:
      positionAtRowLocation in interface ScanController
      Parameters:
      rl - RowLocation for the new position for the scan. The RowLocation submitted should be a RowLocation which has previously been returned by this ScanController.
      Returns:
      true if the scan has been positioned at the RowLocation. false if the scan could not be positioned.
      Throws:
      StandardException - Standard exception policy.
      See Also:
    • getAllScanInfo

      public Properties getAllScanInfo(Properties prop) throws StandardException
      Return all information gathered about the scan.

      This routine returns a list of properties which contains all information gathered about the scan. If a Property is passed in, then that property list is appeneded to, otherwise a new property object is created and returned.

      Currently sort scans doesn't track any information.

      Specified by:
      getAllScanInfo in interface ScanInfo
      Parameters:
      prop - Property list to fill in.
      Throws:
      StandardException - Standard exception policy.
    • isHeldAfterCommit

      public boolean isHeldAfterCommit() throws StandardException
      Description copied from interface: ScanController
      Return true is the scan has been closed after a commit, but was opened with holdability and can be reopened using positionAtRowLocation.
      Specified by:
      isHeldAfterCommit in interface ScanController
      Throws:
      StandardException - Standard exception policy.
      See Also: