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Java > Open Source Codes > org > apache > derby > impl > store > access > conglomerate > GenericCostController


1 /*
2
3    Derby - Class org.apache.derby.impl.store.access.conglomerate.GenericCostController
4
5    Licensed to the Apache Software Foundation (ASF) under one or more
6    contributor license agreements. See the NOTICE file distributed with
7    this work for additional information regarding copyright ownership.
8    The ASF licenses this file to you under the Apache License, Version 2.0
9    (the "License"); you may not use this file except in compliance with
10    the License. You may obtain a copy of the License at
11
12       http://www.apache.org/licenses/LICENSE-2.0
13
14    Unless required by applicable law or agreed to in writing, software
15    distributed under the License is distributed on an "AS IS" BASIS,
16    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17    See the License for the specific language governing permissions and
18    limitations under the License.
19
20  */
21
22 package org.apache.derby.impl.store.access.conglomerate;
23
24 import org.apache.derby.iapi.error.StandardException;
25
26 import org.apache.derby.iapi.reference.SQLState;
27
28 import org.apache.derby.iapi.store.access.StoreCostController;
29 import org.apache.derby.iapi.store.access.StoreCostResult;
30
31 import org.apache.derby.iapi.types.DataValueDescriptor;
32
33 import org.apache.derby.impl.sql.execute.RowUtil;
34
35 import org.apache.derby.iapi.services.io.FormatableBitSet;
36
37
38 /**
39
40 A Generic class which implements the basic functionality needed for a cost
41 controller.
42
43 **/
44
45 public abstract class GenericCostController
46     extends GenericController implements StoreCostController
47 {
48
49     /**************************************************************************
50      * Fields of the class
51      **************************************************************************
52      */
53
54     /**************************************************************************
55      * Constructors for This class:
56      **************************************************************************
57      */
58
59     /**************************************************************************
60      * Private/Protected methods of This class:
61      **************************************************************************
62      */
63
64     /**************************************************************************
65      * Public Methods of This class:
66      **************************************************************************
67      */
68
69     /**************************************************************************
70      * Public Methods implementing StoreCostController class:
71      **************************************************************************
72      */
73
74     /**************************************************************************
75      * Public Methods implementing StoreCostController class, default impl
76      * just throws exception:
77      **************************************************************************
78      */
79
80
81     /**
82      * Return the cost of exact key lookup.
83      * <p>
84      * Return the estimated cost of calling ScanController.fetch()
85      * on the current conglomerate, with start and stop positions set such
86      * that an exact match is expected.
87      * <p>
88      * This call returns the cost of a fetchNext() performed on a scan which
89      * has been positioned with a start position which specifies exact match
90      * on all keys in the row.
91      * <p>
92      * Example:
93      * <p>
94      * In the case of a btree this call can be used to determine the cost of
95      * doing an exact probe into btree, giving all key columns. This cost
96      * can be used if the client knows it will be doing an exact key probe
97      * but does not have the key's at optimize time to use to make a call to
98      * getScanCost()
99      * <p>
100      *
101      * @param validColumns A description of which columns to return from
102      * row on the page into "templateRow." templateRow,
103      * and validColumns work together to
104      * describe the row to be returned by the fetch -
105      * see RowUtil for description of how these three
106      * parameters work together to describe a fetched
107      * "row".
108      *
109      * @param access_type Describe the type of access the query will be
110      * performing to the ScanController.
111      *
112      * STORECOST_CLUSTERED - The location of one scan
113      * is likely clustered "close" to the previous
114      * scan. For instance if the query plan were
115      * to used repeated "reopenScan()'s" to probe
116      * for the next key in an index, then this flag
117      * should be be specified. If this flag is not
118      * set then each scan will be costed independant
119      * of any other predicted scan access.
120      *
121      * @return The cost of the fetch.
122      *
123      * @exception StandardException Standard exception policy.
124      *
125      * @see RowUtil
126      **/
127     public double getFetchFromFullKeyCost(
128     FormatableBitSet validColumns,
129     int access_type)
130         throws StandardException
131     {
132         // Not implemented in default conglomerate, needs to be overridden.
133 throw StandardException.newException(
134                 SQLState.HEAP_UNIMPLEMENTED_FEATURE);
135     }
136
137
138 }
139
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