Oracle Berkeley DB Getting Started with Transaction Processing for C 12c Release 1 Library Version 12.1.6.2 Legal Notice This documentation is distributed under an open source license. You may review the terms of this license at: http:// www.oracle.com/technetwork/database/berkeleydb/downloads/oslicense-093458.html Oracle, Berkeley DB, and Sleepycat are trademarks or registered trademarks of Oracle. All rights to these marks are reserved. No third-party use is permitted without the express prior written consent of Oracle. Other names may be trademarks of their respective owners. To obtain a copy of this document's original source code, please submit a request to the Oracle Technology Network forum at: https://forums.oracle.com/forums/forum.jspa?forumID=271 Published 4/13/2017 Table of Contents Preface ....................................................................................................... v Conventions Used in this Book .................................................................... v For More Information ............................................................................... vi Contact Us ..................................................................................... vi 1. Introduction .............................................................................................. 1 Transaction Benefits ................................................................................. 1 A Note on System Failure .......................................................................... 2 Application Requirements .......................................................................... 2 Multi-threaded and Multi-process Applications ................................................. 4 Recoverability ........................................................................................ 4 Performance Tuning ................................................................................. 5 2. Enabling Transactions .................................................................................. 6 Environments ......................................................................................... 6 File Naming .................................................................................... 7 Specifying the Environment Home Directory ....................................... 7 Specifying File Locations .............................................................. 7 Identifying Specific File Locations ................................................... 8 Error Support ................................................................................. 10 Shared Memory Regions ..................................................................... 10 Regions Backed by Files .............................................................. 11 Regions Backed by Heap Memory ................................................... 11 Regions Backed by System Memory ................................................ 11 Security Considerations ..................................................................... 12 Opening a Transactional Environment and Database ........................................ 13 3. Transaction Basics ..................................................................................... 17 Committing a Transaction ......................................................................... 20 Non-Durable Transactions ......................................................................... 21 Aborting a Transaction ............................................................................ 22 Auto Commit ........................................................................................ 22 Nested Transactions ................................................................................ 25 Transactional Cursors .............................................................................. 26 Secondary Indices with Transaction Applications ............................................. 28 Configuring the Transaction Subsystem ......................................................... 29 4. Concurrency ............................................................................................ 32 Which DB Handles are Free-Threaded .......................................................... 33 Locks, Blocks, and Deadlocks .................................................................... 33 Locks ........................................................................................... 33 Lock Resources ........................................................................ 34 Types of Locks ......................................................................... 34 Lock Lifetime .......................................................................... 35 Blocks .......................................................................................... 35 Blocking and Application Performance ............................................ 36 Avoiding Blocks ........................................................................ 37 Deadlocks ..................................................................................... 38 Deadlock Avoidance ................................................................... 39 The Locking Subsystem ............................................................................ 39 4/13/2017 Using Transactions with DB Page iii Configuring the Locking Subsystem ....................................................... 40 Configuring Deadlock Detection ........................................................... 42 Resolving Deadlocks ......................................................................... 44 Setting Transaction Priorities .............................................................. 46 Isolation .............................................................................................. 47 Supported Degrees of Isolation ............................................................ 48 Reading Uncommitted Data ................................................................ 49 Committed Reads ............................................................................ 51 Using Snapshot Isolation .................................................................... 54 Snapshot Isolation Cost ............................................................... 54 Snapshot Isolation Transactional Requirements .................................. 54 When to Use Snapshot Isolation .................................................... 54 How to use Snapshot Isolation ...................................................... 55 Transactional Cursors and Concurrent Applications ........................................... 57 Using Cursors with Uncommitted Data ................................................... 57 Exclusive Database Handles ...................................................................... 59 Read/Modify/Write ................................................................................. 60 No Wait on Blocks .................................................................................. 61 Reverse BTree Splits ............................................................................... 61 5. Managing DB Files ..................................................................................... 64 Checkpoints ......................................................................................... 64 Backup Procedures ................................................................................. 67 About Unix Copy Utilities .................................................................. 67 Offline Backups .............................................................................. 68 Hot Backup ................................................................................... 68 Incremental Backups ........................................................................ 69 Recovery Procedures ............................................................................... 70 Normal Recovery ............................................................................. 70 Catastrophic Recovery ...................................................................... 72 Designing Your Application for Recovery ....................................................... 73 Recovery for Multi-Threaded Applications ............................................... 73 Recovery in Multi-Process Applications ................................................... 74 Effects of Multi-Process Recovery .................................................. 75 Process Registration ................................................................... 75 Failure Checking ....................................................................... 76 Using Hot Failovers ................................................................................ 77 Removing Log Files ................................................................................. 79 Configuring the Logging Subsystem ............................................................. 80 Setting the Log File Size ................................................................... 80 Configuring the Logging Region Size ...................................................... 81 Configuring In-Memory Logging ............................................................ 81 Setting the In-Memory Log Buffer Size ................................................... 84 6. Summary and Examples .............................................................................. 85 Anatomy of a Transactional Application