01: /*
02:
03: Derby - Class org.apache.derby.iapi.store.raw.xact.TransactionId
04:
05: Licensed to the Apache Software Foundation (ASF) under one or more
06: contributor license agreements. See the NOTICE file distributed with
07: this work for additional information regarding copyright ownership.
08: The ASF licenses this file to you under the Apache License, Version 2.0
09: (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.iapi.store.raw.xact;
23:
24: import org.apache.derby.iapi.services.io.Formatable;
25:
26: /**
27: A transaction identifier that is only unique within a raw store, do not
28: ever pass this out of raw store. During reboot, all transaction Ids that
29: have ever generated a log record will not be reused.
30:
31: However, if you put away the transaction Id of a read only transaction,
32: then the is no guarentee that the transactionId won't be reused when the
33: system reboots. It is much safer to store away the ExternalTrasanctionId
34: rather than the transactionId.
35:
36: The equals() method for TransactionId implements by value equality.
37:
38: MT - immutable
39:
40: */
41: public interface TransactionId extends Formatable {
42:
43: /**
44: Return the maximum number of bytes the transactionId will take
45: to store using writeExternal.
46: */
47: int getMaxStoredSize();
48:
49: /* need to write a value based HashCode() method. */
50: }
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