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2-36 IBM Informix OnLine Database Server Administrator’s Guide
Shared Memory and Process Communication
Shared Memory and Process Communication
Shared memory refers to the use of the same memory segments by more than
one OnLine user process, enabling interprocess communication. Figure 2-4
onpage 2-37showshowmultipleuserprocessescancommunicatebywayof
shared memory.
Interprocess communication via shared memory has the following advan-
tagesoversystemsinwhichserverprocesseseachmaintaintheirownprivate
copy of data:
■ Disk I/O is reduced because buffers, which are managed as a
common pool, are flushed on a system-wide basis instead of a per-
process basis.
■ Execution time is reduced because only one copy of a data or index
page is maintained in shared memory. Processes do not need to
reread shared-memory buffers to ensure that their data is current.
Often, processes do not need to read a page in from disk if the page
is already in shared memory as a result of an earlier query.
- IBM Informix OnLine 1
- Database Server 1
- Table of Contents 3
- Chapter 2 System Architecture 5
- Chapter 3 Operating OnLine 7
- Chapter 6 DB-Monitor Screens 12
- Chapter 7 Utilities 12
- Chapter 8 OnLine Message Log 14
- Chapter 9 Product Environment 14
- Appendix A Notices 14
- Introduction 15
- In This Introduction 17
- About This Manual 17
- Organization of This Manual 18
- Demonstration Database 19
- Documentation Conventions 22
- Icon Conventions 23
- Command-Line Conventions 23
- Sample Code Conventions 26
- Additional Documentation 28
- Error Message Files 29
- Related Reading 33
- IBM Welcomes Your Comments 34
- Installation and Initial 35
- Configuration 35
- Define Your Starting Point 40
- Create a Level-0 Archive 42
- Initialize Shared Memory 42
- Create a New Level-0 Archive 43
- OnLine Configuration Files 45
- Contents of tbconfig.std 47
- # System Page Size 54
- ROOTNAME 55
- ROOTPATH 56
- ROOTOFFSET 56
- ROOTSIZE 57
- MIRRORPATH 58
- MIRROROFFSET 59
- PHYSFILE 59
- PHYSDBS is 1,000 KB 60
- LOGFILES 61
- Message File Guidelines 62
- TAPESIZE 63
- LTAPEDEV 64
- LTAPEBLK 64
- LTAPESIZE 65
- DBSERVERNAME 66
- RESIDENT 66
- TRANSACTIONS 67
- TBLSPACES 68
- DBSPACES 69
- PHYSBUFF 69
- CLEANERS 70
- CKPTINTVL 71
- DYNSHMSZ 73
- GTRID_CMP_SZ 73
- DEADLOCK_TIMEOUT 73
- TXTIMEOUT 73
- OnLine Disk Space Allocation 74
- How to Allocate Disk Space 81
- Configuration Checklist 84
- Set configuration parameters 85
- ESC to record the 86
- Initialize OnLine 88
- TBCONFIG 89
- Shutdown 92
- Errors During Initialization 93
- OnLine Error Message Format 94
- UNIX Error Message Format 94
- System Architecture 95
- System Architecture 2-3 97
- System Architecture 2-5 99
- In This Chapter 101
- Initialization 101
- Initialization Commands 102
- Shared Memory Commands 103
- Disk Space Commands 104
- Step 2: Create Shared Memory 106
- Step 5: Wake Parent Process 107
- ■ tbinit -i 108
- ■ tbinit -i -s 108
- Step 5: Initialize Disk Space 110
- System Architecture 2-17 111
- Step 9: Set Forced Residency 112
- SHMBASE 114
- UNIX system might set a 114
- OnLine User Processes 116
- Step 1: Obtain SERVERNUM 118
- (SERVERNUM * 65536) + shmkey 119
- OnLine Daemon Processes 127
- System Architecture 2-35 129
- LRU queue 129
- Buffer Share Lock 132
- Buffer Update Lock 132
- Buffer Exclusive Lock 133
- ■ Buffer locks 134
- ■ Latches 134
- ■ Timestamps 134
- ■ Hash tables 134
- Shared-Memory Latches 135
- Test-and-Set Institutions 136
- Spin and Test Again 136
- Semaphores 137
- Forced Abort 137
- OnLine Timestamps 138
- System Architecture 2-45 139
- Shared-Memory Header 141
- Shared-Memory Internal Tables 142
- OnLine Chunk Table 143
- OnLine Dbspace Table 144
- OnLine Latch Table 145
- OnLine Lock Table 145
- OnLine Page-Cleaner Table 146
- OnLine Tblspace Table 146
- OnLine Transaction Table 148
- OnLine User Table 148
- Shared-Memory Buffer Pool 149
- Regular Buffers 150
- Big Buffers 150
- OnLine LRU Queues 151
- LRU_MAX_DIRTY 153
- LRU_MIN_DIRTY 153
- Step 1: Identify the Data 155
- Physical Log Buffer 157
- Double Buffering 158
- Causes of Flushing 158
- Flushing a Full Buffer 159
- Logical Log Buffer 160
- Buffer Contents 162
- OnLine Checkpoints 164
- Fast Recovery 165
- Archive Checkpoints 165
- U-L) and frees 166
- System Architecture 2-73 167
- MLRU queues reaches 168
- System Architecture 2-75 169
- LRU write 169
- Sorted Write 170
- Idle Write 170
- Foreground Write 171
- LRU Write 171
- Chunk Write 171
- Writing Data to a Blobspace 172
- Disk Data Structures 175
- I/O is done in units of 176
- BUFFSIZE in the configuration 176
- Blobpage 178
- Dbspace and Blobspace 178
- Database 179
- Tblspace 179
- Physical Log 180
- Logical Log 180
- Structure of the Root Dbspace 181
- ■ Unused pages 183
- Structure of a Blobspace 185
- OnLine Limits for Chunks 187
- Reserved Pages 189
- PAGE_CKPT 191
- PAGE_PZERO 191
- PAGE_CONFIG 191
- PAGE_DBSP 193
- PAGE_PCHUNK 194
- PAGE_MCHUNK 195
- PAGE_ARCH 196
- Chunk Free-List Page 197
- Tblspace Number 199
- Database Tblspace 201
- SQL statement 202
- DATABASE 202
- Allocate Disc Space 203
- Track Systems Catalogs 203
- OnLine Limits for Databases 204
- Placement 207
- Tracking 207
- Structure of an Extent 208
- Page Types 209
- Next Extent Allocation 211
- Structure of a Dbspace Page 214
- Page Header 215
- Timestamp 215
- Slot Table 215
- Data Row Format and Rowid 217
- System Architecture 2-125 219
- Single-Page Storage 220
- Multipage Storage 221
- Storage of Modified Rows 223
- System Architecture 2-131 225
- Structure of an Index Page 227
- The Root Node Page 228
- Leaf Node Pages 230
- Index Key Entries 232
- Branch Node Pages 235
- 2-Bit Bit-Mapped Pages 237
- 4-Bit Bit-Mapped Pages 238
- Blobspace Page Types 242
- Logical Log Files 248
- File Rotation 249
- File Contents 250
- Number and Size 250
- Blobspace Logging 252
- Long Transactions 253
- Operating OnLine 257
- Operating OnLine 3-3 259
- Changing Modes 262
- Operating OnLine 3-7 263
- DB-Monitor 263
- From Offline to Quiescent 264
- From Offline to Online 264
- From Quiescent to Online 265
- From DB-Monitor 266
- From the Command Line 266
- Logical Log Administration 269
- Your Configuration File 270
- Logical Log File Backups 270
- Freeing the Logical Log Files 271
- Configuration Parameters 272
- LTAPEBLK and LTAPESIZE 273
- Location of Logical Log Files 274
- Preliminary Consideration 275
- Logical Log File Status 282
- Logical Log File ID Numbers 283
- Add a Logical Log File 284
- Drop a Logical Log File 286
- ■ End logging for a database 289
- Adding Logging to a Database 290
- Back Up a Logical Log File 292
- Free a Logical Log File 295
- DB-Monitor Force 298
- Archive Administration 299
- Archive Types 300
- Level-0 Archive 300
- Level-1 Archive 301
- Level-2 Archive 301
- Incremental Archive Strategy 301
- Plan the Archive Schedule 303
- Minimize Restore Time 304
- Minimize Archive Time 305
- Online Archives 305
- Single Tape Drive 305
- Operator Availability 306
- The Archives 307
- TAPEBLK and TAPESIZE 308
- Preliminary Considerations 309
- Create an Archive, Any Type 313
- Two Tape Drives 315
- One Tape Drive 316
- Monitor OnLine Activity 317
- Monitor Archive History 318
- Monitor Blobs in a Blobspace 319
- Monitor Blobs in a Dbspace 321
- Monitor Buffers 322
- Monitor Buffer-Pool Activity 324
- Monitor Checkpoints 325
- Monitor Chunks 326
- Monitor Databases 330
- Monitor Dbspaces 331
- Monitor Disk Pages 333
- Monitor Extents 334
- Monitor Index Information 335
- Monitor Logging Activity 336
- Monitor the Message Log 338
- Monitor OnLine Profile 339
- Monitor Tblspaces 341
- Modify OnLine Configuration 343
- Create a Blobspace 344
- Drop a Blobspace 347
- Add a Chunk 350
- Create a Dbspace 353
- Drop a Dbspace 355
- Enforce/Turn Off Residency 356
- Enable Mirroring 360
- Start Mirroring 361
- End Mirroring 362
- Things to Avoid 372
- Data Consistency, Recovery 373
- Consistency Checking 378
- Using the tbcheck Commands 379
- Using the OnLine Message Log 380
- ISAM error is returned: 381
- DUMPCORE 383
- DUMPSHMEM 383
- Recovering from Corruption 384
- Mirroring 386
- Beginning 387
- Processing 388
- Recovery 389
- OnLine Logging Overview 390
- Dbspace Logging 391
- Operations Logging 396
- Operations Rollback 396
- Blob Restoration 397
- Ready LTAPEDEV 399
- Locate the Next Logical Log 399
- Copy Blobpages 399
- Place Log Header on Tape 400
- Write Log Records to Tape 401
- Write Trailer Page 402
- Mount a Tape on TAPEDEV 403
- Verify the Archive Level 404
- Force a Checkpoint 404
- Purpose of Data Snapshot 405
- Archive Disk Pages 406
- Write Tape Header Page 407
- Archive Reserved Pages 408
- Determine Archive Criteria 409
- Write a Trailer Page 410
- Update the Reserved Pages 410
- Fast Recovery and Logging 412
- Step 1: Checkpoint Condition 413
- Verify OnLine Configuration 420
- Mount Level-0 Archive Tape 421
- Verify Current Configuration 422
- Prompt for Logical Log Backup 422
- Roll Forward Logical Logs 423
- Database and Table Migration 424
- UNLOAD/dbschema/LOAD 426
- UNLOAD/dbschema/dbload 426
- ■ UNLOAD /dbschema /LOAD 432
- ■ UNLOAD /dbschema /dbload 432
- Move Files 433
- Using dbexport and dbimport 434
- Using tbunload and tbload 435
- How to Improve Performance 441
- Disk Layout 444
- Blobpage Average Fullness 447
- Apply Effective Criteria 448
- When Is Tuning Needed? 450
- Bufsize Pages/IO Fields 451
- Shared-Memory Buffers 453
- Shared-Memory Resources 454
- Log Buffer Size 455
- How Is Tuning Done? 456
- Page-Cleaner Parameters 457
- Efficient Page Cleaning 458
- Checkpoint Frequency 460
- How Psort Works 462
- Tuning Psort 463
- Psort and Shared Memory 464
- DB-Monitor Screens 467
- Main Menu 470
- Status Menu 471
- Parameters Menu 472
- Dbspaces Menu 473
- Mode Menu 474
- Force-Ckpt Option 475
- Archive Menu 476
- Logical-Logs Menu 477
- Utilities 479
- Utilities 7-3 481
- ■ Lock mode 484
- Destination Options 485
- Contents of the Schema File 487
- ■ Invalid command parameters 489
- Input File Location Options 490
- Create Options 492
- Utilities 7-15 493
- ASCII files into one or 493
- LOAD statement: 493
- ASCII input files 493
- IBM Informix 494
- Utilities 7-17 495
- Command-File Syntax Check 496
- Starting Line Number 496
- Batch Size 497
- Bad-Row Limits 498
- How to Create a Command File 499
- Delimiter Form FILE Statement 500
- ■ Save the output to a file 510
- Include Synonyms 511
- Include Privileges 512
- Option Descriptions 517
- -cd and -cD Options 518
- -ce Option 518
- -ci and -cI Options 518
- -cr Option 519
- -n Option 519
- -pB Option 520
- -pc Option 520
- -pd and -pD Options 520
- -pe Option 521
- -pp and -pP options 521
- -pr Option 522
- -pt and -pT Options 522
- -q Option 523
- -y Option 523
- No Options 524
- -i Option 524
- -p Option 525
- -s Option 525
- DBA privilege for the 526
- Specify Tape Parameters 527
- Utilities 7-51 529
- Log-Record Read Filters 530
- -d Option 531
- Log-Record Display Filters 532
- Interpreting tblog Output 533
- Record Types 534
- Record Contents 535
- Utilities 7-65 543
- Change OnLine Mode 544
- Switch the Logical Log File 546
- Kill an OnLine Server Process 547
- Kill an OnLine Transaction 547
- Utilities 7-73 551
- Create a Blobspace or Dbspace 552
- Drop a Blobspace or Dbspace 553
- Change Chunk Status 555
- Utilities 7-81 559
- -B Option 562
- -c Option 562
- -D Option 564
- -F Option 565
- -k Option 566
- -l Option 567
- -m Option 569
- -o Option 569
- -P Option 573
- -r Option 573
- -R option 573
- -t Option 576
- -u Option 577
- -X Option 579
- -z Option 580
- Utilities 7-103 581
- Request a Logical Log Backup 582
- Start Continuous Backups 582
- Create an Archive 583
- Perform a Data Restore 583
- Utilities 7-107 585
- DB-Monitor Logical-Logs 585
- OnLine Message Log 589
- Alphabetized Messages 593
- Product Environment 621
- The OnLine Environment 623
- OnLine Features 624
- High Performance 624
- Multimedia Support 625
- Distributed Data Queries 626
- Bad-Sector Mapping 626
- What Is Multiple Residency? 627
- How Multiple Residency Works 630
- SERVERNUM 633
- DBSERVER-NAME 633
- Step 5: Initialize New OnLine 634
- DATABASE stores5@italy 636
- BEGIN WORK 636
- COMMIT WORK 636
- Product Environment 9-19 639
- Protocol Components 640
- Example Transaction Commit 641
- Example Transaction Rollback 642
- Coordinator Recovery 643
- SQLEXEC to 644
- Participant Recovery 646
- Product Environment 9-27 647
- TXTIMEOUT. When 647
- Presumed-Abort Optimization 649
- Product Environment 9-31 651
- Product Environment 9-33 653
- Figure 9-8 653
- Product Environment 9-35 655
- Figure 9-9 655
- Heuristic Rollback 656
- Heuristic End-Transaction 660
- Product Environment 9-43 663
- IBM Informix STAR 664
- TABLOCKS 665
- ENDTRANS 665
- Transaction Commit Records 666
- Heuristic Rollback Records 668
- Product Environment 9-53 673
- HEURTX recordassociated with 674
- Example Manual Recovery 675
- DEADLOCK TIMEOUT 677
- TXTIME-OUT 678
- Tracking a Global Transaction 679
- Transaction address Field 679
- Transaction flag Field 680
- Transaction user Field 681
- Transaction locks Field 681
- Transaction log begin 681
- Transaction isolation Field 682
- Transaction retries Field 682
- Transaction coordinator Field 682
- Appendix 683
- Notices A-3 685
- COPYRIGHT LICENSE: 685
- Trademarks 686
- Index 11 697
- Index 13 699
- Index 15 701
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