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Java > Open Source Codes > org > apache > derby > impl > sql > conn > TempTableInfo


1 /*
2
3    Derby - Class org.apache.derby.impl.sql.conn.TempTableInfo
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.sql.conn;
23
24 import org.apache.derby.iapi.error.StandardException;
25 import org.apache.derby.iapi.sql.dictionary.TableDescriptor;
26
27 //this class is for temporary tables. The information kept here is necessary to implement the rollback
28 //and commit behavior for temporary tables.
29
30 /**
31 The temp tables will have following data structure
32 TableDescriptor
33 Declared in savepoint level
34 Dropped in savepoint level
35 Modified in savepoint level
36
37 The actual logic
38
39 LanguageConnectionContext will keep the "current savepoint level". At any point in
40 time, this is the total number of savepoints defined for a transaction.
41 At the start of any new transaction, the "current savepoint level" will be set to 0.
42
43 Everytime a new user defined savepoint is set, store returns the total number of savepoints
44 for the connection at that point.
45 For eg, in a new transaction,
46 "current savepoint level' will be 0. When the first savepoint is set, store will return
47 1 and "current savepoint level" will be set to 1. For next savepoint, store will return 2 and so on
48 and so forth.
49
50 When language calls rollback or release of a savepoint, store will again return the total number of savepoints
51 for the connection after rollback or release and we will set "current savepoint level" to that number. For eg,
52 start tran ("current savepoint level"=0)
53 set savepoint 1 ("current savepoint level"=1)
54 set savepoint 2 ("current savepoint level"=2)
55 set savepoint 3 ("current savepoint level"=3)
56 set savepoint 4 ("current savepoint level"=4)
57 release savepoint 3 ("current savepoint level"=2)
58 rollback savepoint 1 ("current savepoint level"=0)
59
60 If the temporary table was declared with ON ROLLBACK DELETE ROWS and contents of that temporary table
61 were modified in a transaction or within a savepoint unit, then we keep track of that by saving the
62 savepoint level in dataModifiedInSavepointLevel. This information will be used at rollback of savepoint or transaction.
63 Also, when a savepoint is released, we check if the table was modified in any of the savepoints that
64 are getting released. If yes, then we put the current savepoint level as dataModifiedInSavepointLevel.
65 eg
66 start tran ("current savepoint level"=0)
67 declare temp table 0 ON ROLLBACK DELETE ROWS("declared in savepoint level"=0, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
68 commit (temp table 0 ("declared in savepoint level"=-1, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1))
69 start tran ("current savepoint level = 0)
70   temp table 0 ("declared in savepoint level"=-1, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
71 set savepoint 1("current savepoint level = 1")
72   temp table 0 ("declared in savepoint level"=-1, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
73 set savepoint 2("current savepoint level = 2")
74   delete 1 row from temp table 0
75   temp table 0 ("declared in savepoint level"=-1, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=2)
76 release savepoint 2 ("current savepoint level"=1) and reset the modified in savepoint level as follows
77   temp table 0 ("declared in savepoint level"=-1, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=1)
78 rollback ("current savepoint level"=0) All the rows from the temp table 0 will be removed
79 At the time of commit, we set dataModifiedInSavepointLevel to -1.
80 At the time of rollback (transaction / savepoint), first we check if the table was modified in the unit of work
81 getting rolled back. If yes, then we delete all the data from the temp table and we set dataModifiedInSavepointLevel to -1.
82
83 When language calls release of a savepoint, store will again return the total number of savepoints
84 in the system after release. We will go through all the temp tables and reset their declared or
85 dropped or modified in savepoint level to the value returned by the release savepoint if those tables had their
86 declared or dropped or modified in savepoint levels higher than what was returned by the release savepoint.
87 eg
88 start tran ("current savepoint level"=0)
89 declare temp table 0 ("declared in savepoint level"=0, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
90 set savepoint 1("current savepoint level = 1")
91 declare temp table 1 ("declared in savepoint level"=1, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
92 set savepoint 2("current savepoint level = 2")
93 declare temp table 2 ("declared in savepoint level"=2, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
94 release savepoint 1 ("current savepoint level"=0) and reset the savepoint levels as follows
95   temp table 1 ("declared in savepoint level"=0, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
96   temp table 2 ("declared in savepoint level"=0, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
97 set savepoint 3("current savepoint level = 1")
98 rollback savepoint 3 ("current savepoint level"=0) and temp table info will look as follows
99   temp table 0 ("declared in savepoint level"=0, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
100   temp table 1 ("declared in savepoint level"=0, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
101   temp table 2 ("declared in savepoint level"=0, "dropped in savepoint level"=-1, "dataModifiedInSavepointLevel"=-1)
102
103 When you declare a temp table, it will have "declared in savepoint level" as the current savepoint
104 level of the LanguageConnectionContext (which will be 0 in a transaction with no user-defined savepoints).
105 The "dropped in savepoint level" for new temp tables will be set to -1.
106 The "dataModifiedInSavepointLevel" for new temp tables will be set to -1 as well.
107
108 When a temp table is dropped, we will first check if the table was declared in a savepoint level
109 equal to the current savepoint level.
110     If yes, then we will remove it from the temp tables list for the LanguageConnectionContext .
111     eg
112     start tran ("current savepoint level = 0")
113     set savepoint 1("current savepoint level = 1")
114     declare temp table 1 ("declared in savepoint level"=1, "dropped in savepoint level"=-1)
115     drop temp table 1 (declared in savepoint level same as current savepoint level and hence will remove it from list of temp tables)
116     If no, then we will set the dropped in savepoint level as the current savepoint level of the
117         LanguageConnectionContext (which will be 0 in a transaction without savepoints and it also means
118         that the table was declared in a previous transaction).
119
120 At the time of commit, go through all the temp tables with "dropped in savepoint level" != -1 (meaning dropped in this transaction)
121 and remove them from the temp tables list for the LanguageConnectionContext. All the rest of the temp tables with
122 "dropped in savepoint level" = -1, we will set their "declared in savepoint level" to -1 and , "dataModifiedInSavepointLevel" to -1.
123 eg
124   start tran ("current savepoint level = 0)
125       declare temp table t1("declared in savepoint level" = 0, "dropped in savepoint level"=-1)
126   commit (temp table 1 ("declared in savepoint level"=-1, "dropped in savepoint level"=-1))
127   start tran ("current savepoint level = 0)
128       drop temp table t1 ("declared in savepoint level" = -1, "dropped in savepoint level"=0)
129   commit (temp table t1 will be removed from list of temp tables)
130
131 At the time of rollback
132   if rolling back transaction, first set the "current savepoint level" to 0
133   if rolling back to a savepoint, first set the "current savepoint level" to savepoint level returned by Store
134     for the rollback to savepoint command
135   Now go through all the temp tables.
136     If "declared in savepoint level" of temp table is greater than or equal to "current savepoint level"
137   (ie table was declared in this unit of work)
138     And if table was not dropped in this unit of work ie "dropped in savepoint level" = -1
139       Then we should remove the table from the list of temp tables and drop the conglomerate created for it
140           eg
141           start tran ("current savepoint level = 0)
142         declare temp table t2("declared in savepoint level" = 0, "dropped in savepoint level"=-1)
143           rollback tran
144         (temp table t2 will be removed from list of tables and conglomerate associated with it will be dropped)
145     And if table was dropped in this unit of work ie "dropped in savepoint level" >= "current savepoint level"
146       Then we should remove the table from the list of temp tables
147           eg
148           start tran ("current savepoint level = 0)
149       set savepoint 1("current savepoint level = 1")
150         declare temp table t2("declared in savepoint level" = 1, "dropped in savepoint level"=-1)
151       set savepoint 2("current savepoint level = 2")
152           drop temp table t1 ("declared in savepoint level" = 1, "dropped in savepoint level"=2)
153           rollback savepoint 1 ("current savepoint level = 0) temp table t1 will be removed from the list of temp tables
154     Else if the "dropped in savepoint level" of temp table is greate than or equal to "current savepoint level"
155         it mean that table was dropped in this unit of work (and was declared in an earlier savepoint unit / transaction) and we will
156     restore it as part of rollback ie replace the existing entry for this table in valid temp tables list with restored temp table.
157     At the end of restoring, "declared in savepoint level" will remain unchanged and "dropped in savepoint level" will be -1.
158         eg
159           start tran ("current savepoint level = 0)
160           declare temp table t1 with definition 1("declared in savepoint level" = 0, "dropped in savepoint level"=-1, definition 1(stored in table descriptor))
161           commit (temp table t1 "declared in savepoint level" = -1, "dropped in savepoint level"=-1)
162           start tran ("current savepoint level = 0)
163       set savepoint 1("current savepoint level = 1")
164           drop temp table t1 ("declared in savepoint level" = -1, "dropped in savepoint level"=1, definition 1(stored in table descriptor))
165           declare temp table t1 with definition 2(say different than definition 1)
166         ("declared in savepoint level" = -1, "dropped in savepoint level"=1, definition 1(stored in table descriptor)) ,
167               ("declared in savepoint level" = 1, "dropped in savepoint level"=-1, definition 2(stored in table descriptor))
168       set savepoint 2("current savepoint level = 2")
169       drop temp table t1("declared in savepoint level" = -1, "dropped in savepoint level"=1, definition 1(stored in table descriptor)) ,
170               ("declared in savepoint level" = 1, "dropped in savepoint level"=2, definition 2(stored in table descriptor))
171           rollback tran
172         (Remove : temp table t1("declared in savepoint level" = 1, "dropped in savepoint level"=2, definition 2(stored in table descriptor)
173         (Restore : temp table t1"declared in savepoint level" = -1, "dropped in savepoint level"=-1, definition 1(stored in table descriptor))
174     Else if the "dataModifiedInSavepointLevel" of temp table is greate than or equal to "current savepoint level"
175         it means that table was declared in an earlier savepoint unit / transaction and was modified in the current UOW. And hence we will delete all the
176     data from it.
177 */
178 class TempTableInfo
179 {
180
181     private TableDescriptor td;
182     private int declaredInSavepointLevel;
183     private int droppededInSavepointLevel;
184     private int dataModifiedInSavepointLevel;
185
186     TempTableInfo(TableDescriptor td, int declaredInSavepointLevel)
187     {
188         this.td = td;
189         this.declaredInSavepointLevel = declaredInSavepointLevel;
190         this.droppededInSavepointLevel = -1;
191         this.dataModifiedInSavepointLevel = -1;
192     }
193
194     /**
195      * Return the table descriptor
196      */
197     TableDescriptor getTableDescriptor() {
198     return td;
199   }
200
201     /**
202      * Set the table descriptor. Will be called while temporary is being restored
203      */
204     void setTableDescriptor(TableDescriptor td) {
205     this.td = td;
206   }
207
208     /**
209      * Matches by name and only temp tables that have not been dropped (that's when droppededInSavepointLevel will be -1)
210      */
211     boolean matches(String JavaDoc tableName) {
212     return (td.getName().equals(tableName) && droppededInSavepointLevel == -1);
213   }
214
215     /**
216      * Return the savepoint level when the table was last modified
217      */
218     int getModifiedInSavepointLevel() {
219     return dataModifiedInSavepointLevel;
220   }
221
222     /**
223      * Set the savepoint level when the table was last modified
224      */
225     void setModifiedInSavepointLevel(int dataModifiedInSavepointLevel) {
226     this.dataModifiedInSavepointLevel = dataModifiedInSavepointLevel;
227   }
228
229     /**
230      * Return the savepoint level when the table was declared
231      */
232     int getDeclaredInSavepointLevel() {
233     return declaredInSavepointLevel;
234   }
235
236     /**
237      * Set the savepoint level when the table was declared
238      */
239     void setDeclaredInSavepointLevel(int declaredInSavepointLevel) {
240     this.declaredInSavepointLevel = declaredInSavepointLevel;
241   }
242
243     /**
244      * Return the savepoint level when the table was dropped
245      */
246     int getDroppedInSavepointLevel() {
247     return droppededInSavepointLevel;
248   }
249
250     /**
251      * Return the savepoint level when the table was dropped
252      */
253     public void setDroppedInSavepointLevel(int droppededInSavepointLevel) {
254     this.droppededInSavepointLevel = droppededInSavepointLevel;
255   }
256 }
257
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