org.apache.derby.iapi.store.access.conglomerate
Interface ScanManager

All Superinterfaces:
GenericScanController, GroupFetchScanController, RowCountable, ScanController
All Known Implementing Classes:
BTreeScan, GenericScanController, HeapScan, Scan

public interface ScanManager
extends ScanController, GroupFetchScanController

The ScanManager interface contains those methods private to access method implementors necessary to implement Scans on Conglomerates. Client of scans use the ScanController to interact with the scan.

See Also:
ScanController

Field Summary
 
Fields inherited from interface org.apache.derby.iapi.store.access.ScanController
GE, GT, NA
 
Method Summary
 boolean closeForEndTransaction(boolean closeHeldScan)
          Close scan as part of terminating a transaction.
 void fetchSet(long max_rowcnt, int[] key_column_numbers, BackingStoreHashtable hash_table)
          Insert all rows that qualify for the current scan into the input Hash table.
 void savePosition(Conglomerate conglom, Page page)
          Do work necessary to maintain the current position in the scan.
 
Methods inherited from interface org.apache.derby.iapi.store.access.ScanController
delete, didNotQualify, doesCurrentPositionQualify, fetch, fetchLocation, fetchNext, isCurrentPositionDeleted, next, replace
 
Methods inherited from interface org.apache.derby.iapi.store.access.GenericScanController
close, getScanInfo, isKeyed, isTableLocked, newRowLocationTemplate, reopenScan, reopenScanByRowLocation
 
Methods inherited from interface org.apache.derby.iapi.store.access.RowCountable
getEstimatedRowCount, setEstimatedRowCount
 
Methods inherited from interface org.apache.derby.iapi.store.access.GroupFetchScanController
fetchNextGroup, fetchNextGroup, next
 

Method Detail

closeForEndTransaction

public boolean closeForEndTransaction(boolean closeHeldScan)
                               throws StandardException
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 - 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 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.
Throws:
StandardException - Standard exception policy.

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.

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 Vector 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 Vector 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?

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 - 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).
Returns:
boolean indicating that the fetch set succeeded. If it failed Hashtable.clear() will be called leaving an empty table.
Throws:
StandardException - Standard exception policy.

savePosition

public void savePosition(Conglomerate conglom,
                         Page page)
                  throws StandardException
Do work necessary to maintain the current position in the scan.

The latched page in the conglomerate "congomid" is changing, do whatever is necessary to maintain the current position of the scan. For some conglomerates this may be a no-op.

Parameters:
conglom - Conglomerate object of the conglomerate being changed.
page - Page in the conglomerate being changed.
Throws:
StandardException - Standard exception policy.

Built on Tue 2006-10-10 19:23:47+0200, from revision exported

Apache Derby V10.1 Engine Documentation - Copyright © 1997,2005 The Apache Software Foundation or its licensors, as applicable.