public abstract Class GenericScanController

Constants of the class

Overrides org.apache.derby.impl.store.access.conglomerate.GenericController.close.

Implements org.apache.derby.iapi.store.access.GenericScanController.close.

Doc from org.apache.derby.iapi.store.access.GenericScanController.close.

Close the scan. This method always succeeds, and never throws any exceptions. Callers must not use the scan controller after closing it; they are strongly advised to clear out the scan controller reference after closing.

Exceptions

StandardException:

Standard exception policy.

Implements org.apache.derby.iapi.store.access.conglomerate.ScanManager.closeForEndTransaction.

Doc from org.apache.derby.iapi.store.access.conglomerate.ScanManager.closeForEndTransaction.

Close scan as part of terminating a transaction.

Use this call to close the scan resources as part of committing or aborting a transaction. The normal close() routine may do some cleanup that is either unnecessary, or not correct due to the unknown condition of the scan following a transaction ending error. Use this call when closing all scans as part of an abort of a transaction.

Parameters

closeHeldScan:boolean

If true, means to close scan even if it has been opened to be kept opened across commit. This is used to close these scans on abort.

Returns:boolean

boolean indicating that the close has resulted in a real close of the scan. A held scan will return false if called by closeForEndTransaction(false), otherwise it will return true. A non-held scan will always return true.

Exceptions

StandardException:

Standard exception policy.

Implements org.apache.derby.iapi.store.access.ScanController.delete.

Doc from org.apache.derby.iapi.store.access.ScanController.delete.

Delete the row at the current position of the scan.

Returns:boolean

true if the delete was successful, false if the current position is no longer valid (ie. if it was already deleted).

Exceptions

StandardException:

Standard exception policy.

See Also

org.apache.derby.iapi.store.access.ScanController#delete

Implements org.apache.derby.iapi.store.access.ScanController.didNotQualify.

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. RESOLVE (mikem-05/29/98) - Implement this when we support levels of concurrency less than serializable.

Exceptions

StandardException:

Standard exception policy.

Implements org.apache.derby.iapi.store.access.ScanController.doesCurrentPositionQualify.

Returns true if the current position of the scan still qualifies under the set of qualifiers passed to the openScan(). When called this routine will reapply all qualifiers against the row currently positioned and return true if the row still qualifies. If the row has been deleted or no longer passes the qualifiers then this routine will return false. This case can come about if the current scan or another scan on the same table in the same transaction deleted the row or changed columns referenced by the qualifier after the next() call which positioned the scan at this row. Note that for comglomerates which don't support update, like btree's, there is no need to recheck the qualifiers. The results of a fetch() performed on a scan positioned on a deleted row are undefined.

Exceptions

StandardException:

Standard exception policy.

Implements org.apache.derby.iapi.store.access.ScanController.fetch.

Fetch the row at the current position of the Scan.

Parameters

row:DataValueDescriptor[]

Doc from org.apache.derby.iapi.store.access.ScanController.fetch.

The row into which the value of the current position in the scan is to be stored.

Exceptions

StandardException:

Doc from org.apache.derby.iapi.store.access.ScanController.fetch.

Standard exception policy.

See Also

org.apache.derby.iapi.store.access.ScanController#fetch

Implements org.apache.derby.iapi.store.access.ScanController.fetchLocation.

Fetch the location of the current position in the scan.

Exceptions

StandardException:

Standard exception policy.

See Also

org.apache.derby.iapi.store.access.ScanController#fetchLocation

Implements org.apache.derby.iapi.store.access.conglomerate.ScanManager.fetchSet.

Insert all rows that qualify for the current scan into the input Hash table.

This routine scans executes the entire scan as described in the openScan call. For every qualifying unique row value an entry is placed into the HashTable. For unique row values the entry in the Hashtable has a key value of the object stored in row[key_column_number], and the value of the data is row. For row values with duplicates, the key value is also row[key_column_number], but the value of the data is a List of rows. The caller will have to call "instanceof" on the data value object if duplicates are expected, to determine if the data value of the Hashtable entry is a row or is a List of rows.

Note, that for this routine to work efficiently the caller must ensure that the object in row[key_column_number] implements the hashCode and equals method as appropriate for it's datatype.

It is expected that this call will be the first and only call made in an openscan. Qualifiers and stop position of the openscan are applied just as in a normal scan. This call is logically equivalent to the caller performing the following:

import java.util.Hashtable;

hash_table = new Hashtable();

while (next())
{
    row = create_new_row();
    fetch(row);
    if ((duplicate_value = 
        hash_table.put(row[key_column_number], row)) != null)
    {
        Vector row_vec;

        // inserted a duplicate
        if ((duplicate_value instanceof vector))
        {
            row_vec = (Vector) duplicate_value;
        }
        else
        {
            // allocate vector to hold duplicates
            row_vec = new Vector(2);

            // insert original row into vector
            row_vec.addElement(duplicate_value);

            // put the vector as the data rather than the row
            hash_table.put(row[key_column_number], row_vec);
        }

        // insert new row into vector
        row_vec.addElement(row);
    }
}

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. RESOLVE - is this ok? or should I hard code somehow the row to be the first column and the row location?

Currently it is only possible to hash on the first column in the conglomerate, in the future we may change the interface to allow hashing either on a different column or maybe on a combination of columns.

No overflow to external storage is provided, so calling this routine on a 1 gigabyte conglomerate will incur at least 1 gigabyte of memory (probably failing with a java out of memory condition). If this routine gets an out of memory condition, or if "max_rowcnt" is exceeded then then the routine will give up, empty the Hashtable, and return "false."

On exit from this routine, whether the fetchSet() succeeded or not the scan is complete, it is positioned just the same as if the scan had been drained by calling "next()" until it returns false (ie. fetchNext() and next() calls will return false). reopenScan() can be called to restart the scan.

RESOLVE - until we get row counts what should we do for sizing the the size, capasity, and load factor of the hash table. For now it is up to the caller to create the Hashtable, Access does not reset any parameters.

RESOLVE - I am not sure if access should be in charge of allocating the new row objects. I know that I can do this in the case of btree's, but I don't think I can do this in heaps. Maybe this is solved by work to be done on the sort interface.

Parameters

max_rowcnt:long

The maximum number of rows to insert into the Hash table. Pass in -1 if there is no maximum.

key_column_numbers:int[]

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 column in the row in the table of the scan).

hash_table:BackingStoreHashtable

The java HashTable to load into.

Exceptions

StandardException:

Standard exception policy.

Implements org.apache.derby.iapi.store.access.ScanController.fetchWithoutQualify.

Fetch the row at the current position of the Scan without applying the qualifiers.

Parameters

row:DataValueDescriptor[]

Doc from org.apache.derby.iapi.store.access.ScanController.fetchWithoutQualify.

The row into which the value of the current position in the scan is to be stored.

Exceptions

StandardException:

Doc from org.apache.derby.iapi.store.access.ScanController.fetchWithoutQualify.

Standard exception policy.

See Also

org.apache.derby.iapi.store.access.ScanController#fetchWithoutQualify

Implements org.apache.derby.iapi.store.access.GenericScanController.getScanInfo.

Return ScanInfo object which describes performance of scan.

Return ScanInfo object which contains information about the current scan.

Returns:ScanInfo

The ScanInfo object which contains info about current scan.

Exceptions

StandardException:

Standard exception policy.

See Also

ScanInfo

Public Methods of This class:

Implements org.apache.derby.iapi.store.access.ScanController.isCurrentPositionDeleted.

Returns true if the current position of the scan is at a deleted row. This case can come about if the current scan or another scan on the same table in the same transaction deleted the row after the next() call which positioned the scan at this row. The results of a fetch() performed on a scan positioned on a deleted row are undefined.

Exceptions

StandardException:

Standard exception policy.

Implements org.apache.derby.iapi.store.access.ScanController.isHeldAfterCommit.

Doc from org.apache.derby.iapi.store.access.ScanController.isHeldAfterCommit.

Return true is the scan has been closed after a commit, but was opened with holdability and can be reopened using positionAtRowLocation.

Exceptions

StandardException:

Standard exception policy.

See Also

org.apache.derby.iapi.store.access.ScanController#isHeldAfterCommit

Implements org.apache.derby.iapi.store.access.GenericScanController.reopenScan.

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 with against the same conglomerate, and the scan is reopened with the same "hold" and "forUpdate" parameters passed in the original openScan. The previous template row continues to be used.

Parameters

startKeyValue:DataValueDescriptor[]

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:int

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: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:DataValueDescriptor[]

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:int

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.

Exceptions

StandardException:

Standard exception policy.

Implements org.apache.derby.iapi.store.access.GenericScanController.reopenScanByRowLocation.

Doc from org.apache.derby.iapi.store.access.GenericScanController.reopenScanByRowLocation.

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.

Parameters

startRowLocation:RowLocation

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: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.

Exceptions

StandardException:

Standard exception policy.

Implements org.apache.derby.iapi.store.access.ScanController.replace.

Doc from org.apache.derby.iapi.store.access.ScanController.replace.

Replace the (partial) row at the current position of the scan.

Returns:boolean

true if the replace was successful, false if the current position is no longer valid (ie. if it was deleted).

Exceptions

StandardException:

Standard exception policy.

See Also

org.apache.derby.iapi.store.access.ScanController#replace