Class HeapScan

    • Field Detail

      • fetchNext_one_slot_array

        private DataValueDescriptor[][] fetchNext_one_slot_array
        A 1 element array to turn fetchNext and fetch calls into fetchNextGroup calls.
    • Constructor Detail

      • HeapScan

        public HeapScan()
        The only constructor for a heap scan returns a scan in the closed state, the caller must call open.
    • Method Detail

      • reopenScanByRecordHandleAndSetLocks

        private boolean reopenScanByRecordHandleAndSetLocks​(RecordHandle rh)
                                                     throws StandardException
        Reposition the current scan and sets the necessary locks.
        Parameters:
        rh - An existing RecordHandle 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.
        Returns:
        true if the scan was successfully repositioned
        Throws:
        StandardException - Standard exception policy.
      • fetchNext

        public boolean fetchNext​(DataValueDescriptor[] fetch_row)
                          throws StandardException
        Fetch the row at the next position of the Scan. If there is a valid next position in the scan then the value in the template storable row is replaced with the value of the row at the current scan position. The columns of the template row must be of the same type as the actual columns in the underlying conglomerate. The resulting contents of templateRow after a fetchNext() which returns false is undefined. The result of calling fetchNext(row) is exactly logically equivalent to making a next() call followed by a fetch(row) call. This interface allows implementations to optimize the 2 calls if possible.
        Specified by:
        fetchNext in interface ScanController
        Parameters:
        fetch_row - The template row into which the value of the next position in the scan is to be stored.
        Returns:
        True if there is a next position in the scan, false if there isn't.
        Throws:
        StandardException - Standard exception policy.
        See Also:
        ScanController.fetch(org.apache.derby.iapi.types.DataValueDescriptor[]), RowUtil
      • next

        public boolean next()
                     throws StandardException
        Description copied from interface: ScanController
        Move to the next position in the scan. If this is the first call to next(), the position is set to the first row. Returns false if there is not a next row to move to. It is possible, but not guaranteed, that this method could return true again, after returning false, if some other operation in the same transaction appended a row to the underlying conglomerate.
        Specified by:
        next in interface GroupFetchScanController
        Specified by:
        next in interface ScanController
        Returns:
        True if there is a next position in the scan, false if there isn't.
        Throws:
        StandardException - Standard exception policy.
        See Also:
        ScanController.next()
      • 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:
        ScanController.positionAtRowLocation(org.apache.derby.iapi.types.RowLocation)
      • fetchNextGroup

        public int fetchNextGroup​(DataValueDescriptor[][] row_array,
                                  RowLocation[] rowloc_array)
                           throws StandardException
        Description copied from interface: GroupFetchScanController
        Fetch the next N rows from the table.

        The client allocates an array of N rows and passes it into the fetchNextSet() call. The client must at least allocate a row and set row_array[0] to this row. The client can optionally either leave the rest of array entries null, or allocate rows to the slots. If access finds an entry to be null, and wants to read a row into it, it will allocate a row to the slot. Once fetchNextGroup() returns "ownership" of the row passes back to the client, access will not keep references to the allocated row. Expected usage is that the client will specify an array of some number (say 10), and then only allocate a single row. This way if only 1 row qualifies only one row will have been allocated.

        This routine does the equivalent of N fetchNext() calls, filling in each of the rows in the array. Locking is performed exactly as if the N fetchNext() calls had been made.

        It is up to Access how many rows to return. fetchNextGroup() will return how many rows were filled in. If fetchNextGroup() returns 0 then the scan is complete, (ie. the scan is in the same state as if fetchNext() had returned false). If the scan is not complete then fetchNext() will return (1 <= row_count <= N).

        The current position of the scan is undefined if fetchNextSet() is used (ie. mixing fetch()/fetchNext() and fetchNextSet() calls in a single scan does not work). This is because a fetchNextSet() request for 5 rows from a heap where the first 2 rows qualify, but no other rows qualify will result in the scan being positioned at the end of the table, while if 5 rows did qualify the scan will be positioned on the 5th row.

        If the row loc array is non-null then for each row fetched into the row array, a corresponding fetchLocation() call will be made to fill in the rowloc_array. This array, like the row array can be initialized with only one non-null RowLocation and access will allocate the rest on demand.

        Qualifiers, start and stop positioning of the openscan are applied just as in a normal scan.

        The columns of the row will be the standard columns returned as part of a scan, as described by the validColumns - see openScan for description.

        Expected usage: // allocate an array of 5 empty rows DataValueDescriptor[][] row_array = allocate_row_array(5); int row_cnt = 0; scan = openScan(); while ((row_cnt = scan.fetchNextSet(row_array, null) != 0) { // I got "row_cnt" rows from the scan. These rows will be // found in row_array[0] through row_array[row_cnt - 1] }

        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.
      • 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.

        The statistics gathered by the scan are not reset to 0 by a reopenScan(), rather they continue to accumulate.

        Note that this operation is currently only supported on Heap conglomerates. Also note that order of rows within are heap are not guaranteed, so for instance positioning at a RowLocation in the "middle" of a heap, then inserting more data, then continuing the scan is not guaranteed to see the new rows - they may be put in the "beginning" of the heap.

        Specified by:
        reopenScanByRowLocation in interface GenericScanController
        Overrides:
        reopenScanByRowLocation in class 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.