latest/php/api/caches/index.html

   1
   2 <!doctype html>
   3 <html lang="en" class="no-js">
   4   <head>
   5
   6       <meta charset="utf-8">
   7       <meta name="viewport" content="width=device-width,initial-scale=1">
   8
   9
  10
  11
  12       <link rel="icon" href="../../../assets/default.favicon.ico">
  13       <meta name="generator" content="mkdocs-1.1.2, mkdocs-material-7.1.0">
  14
  15
  16
  17         <title>Overview - WoltLab Suite Documentation</title>
  18
  19
  20
  21       <link rel="stylesheet" href="../../../assets/stylesheets/main.33e2939f.min.css">
  22
  23
  24         <link rel="stylesheet" href="../../../assets/stylesheets/palette.ef6f36e2.min.css">
  25
  26
  27
  28           <meta name="theme-color" content="#009485">
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38       <link rel="stylesheet" href="../../../stylesheets/extra.css">
  39
  40
  41
  42
  43
  44   </head>
  45
  46
  47
  48
  49
  50
  51
  52     <body dir="ltr" data-md-color-scheme="" data-md-color-primary="teal" data-md-color-accent="">
  53
  54
  55     <script>function __prefix(e){return new URL("../../..",location).pathname+"."+e}function __get(e,t=localStorage){return JSON.parse(t.getItem(__prefix(e)))}</script>
  56
  57     <input class="md-toggle" data-md-toggle="drawer" type="checkbox" id="__drawer" autocomplete="off">
  58     <input class="md-toggle" data-md-toggle="search" type="checkbox" id="__search" autocomplete="off">
  59     <label class="md-overlay" for="__drawer"></label>
  60     <div data-md-component="skip">
  61
  62
  63         <a href="#caches" class="md-skip">
  64           Skip to content
  65         </a>
  66
  67     </div>
  68     <div data-md-component="announce">
  69
  70         <aside class="md-announce">
  71           <div class="md-announce__inner md-grid md-typeset">
  72
  73     <a href="https://www.woltlab.com">Back to <strong>woltlab.com</strong></a>
  74
  75           </div>
  76         </aside>
  77
  78     </div>
  79
  80       <header class="md-header" data-md-component="header">
  81   <nav class="md-header__inner md-grid" aria-label="Header">
  82     <a href="../../.." title="WoltLab Suite Documentation" class="md-header__button md-logo" aria-label="WoltLab Suite Documentation" data-md-component="logo">
  83
  84   <img src="../../../assets/logo.png" alt="logo">
  85
  86     </a>
  87     <label class="md-header__button md-icon" for="__drawer">
  88       <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M3 6h18v2H3V6m0 5h18v2H3v-2m0 5h18v2H3v-2z"/></svg>
  89     </label>
  90     <div class="md-header__title" data-md-component="header-title">
  91       <div class="md-header__ellipsis">
  92         <div class="md-header__topic">
  93           <span class="md-ellipsis">
  94             WoltLab Suite Documentation
  95           </span>
  96         </div>
  97         <div class="md-header__topic" data-md-component="header-topic">
  98           <span class="md-ellipsis">
  99
 100               Overview
 101
 102           </span>
 103         </div>
 104       </div>
 105     </div>
 106
 107
 108
 109       <label class="md-header__button md-icon" for="__search">
 110         <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5z"/></svg>
 111       </label>
 112
 113 <div class="md-search" data-md-component="search" role="dialog">
 114   <label class="md-search__overlay" for="__search"></label>
 115   <div class="md-search__inner" role="search">
 116     <form class="md-search__form" name="search">
 117       <input type="text" class="md-search__input" name="query" aria-label="Search" placeholder="Search" autocapitalize="off" autocorrect="off" autocomplete="off" spellcheck="false" data-md-component="search-query" data-md-state="active" required>
 118       <label class="md-search__icon md-icon" for="__search">
 119         <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5z"/></svg>
 120         <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12z"/></svg>
 121       </label>
 122       <button type="reset" class="md-search__icon md-icon" aria-label="Clear" tabindex="-1">
 123         <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M19 6.41 17.59 5 12 10.59 6.41 5 5 6.41 10.59 12 5 17.59 6.41 19 12 13.41 17.59 19 19 17.59 13.41 12 19 6.41z"/></svg>
 124       </button>
 125     </form>
 126     <div class="md-search__output">
 127       <div class="md-search__scrollwrap" data-md-scrollfix>
 128         <div class="md-search-result" data-md-component="search-result">
 129           <div class="md-search-result__meta">
 130             Initializing search
 131           </div>
 132           <ol class="md-search-result__list"></ol>
 133         </div>
 134       </div>
 135     </div>
 136   </div>
 137 </div>
 138
 139
 140       <div class="md-header__source">
 141
 142 <a href="https://github.com/WoltLab/docs.woltlab.com/" title="Go to repository" class="md-source" data-md-component="source">
 143   <div class="md-source__icon md-icon">
 144
 145     <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81z"/></svg>
 146   </div>
 147   <div class="md-source__repository">
 148     GitHub
 149   </div>
 150 </a>
 151       </div>
 152
 153   </nav>
 154 </header>
 155
 156     <div class="md-container" data-md-component="container">
 157
 158
 159
 160
 161       <main class="md-main" data-md-component="main">
 162         <div class="md-main__inner md-grid">
 163
 164
 165
 166               <div class="md-sidebar md-sidebar--primary" data-md-component="sidebar" data-md-type="navigation" >
 167                 <div class="md-sidebar__scrollwrap">
 168                   <div class="md-sidebar__inner">
 169
 170
 171
 172 <nav class="md-nav md-nav--primary" aria-label="Navigation" data-md-level="0">
 173   <label class="md-nav__title" for="__drawer">
 174     <a href="../../.." title="WoltLab Suite Documentation" class="md-nav__button md-logo" aria-label="WoltLab Suite Documentation" data-md-component="logo">
 175
 176   <img src="../../../assets/logo.png" alt="logo">
 177
 178     </a>
 179     WoltLab Suite Documentation
 180   </label>
 181
 182     <div class="md-nav__source">
 183
 184 <a href="https://github.com/WoltLab/docs.woltlab.com/" title="Go to repository" class="md-source" data-md-component="source">
 185   <div class="md-source__icon md-icon">
 186
 187     <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81z"/></svg>
 188   </div>
 189   <div class="md-source__repository">
 190     GitHub
 191   </div>
 192 </a>
 193     </div>
 194
 195   <ul class="md-nav__list" data-md-scrollfix>
 196
 197
 198
 199
 200
 201
 202
 203
 204     <li class="md-nav__item">
 205       <a href="../../../getting-started/" class="md-nav__link">
 206         Getting Started
 207       </a>
 208     </li>
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222     <li class="md-nav__item md-nav__item--active md-nav__item--nested">
 223
 224
 225         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_2" type="checkbox" id="__nav_2" checked>
 226
 227       <label class="md-nav__link" for="__nav_2">
 228         PHP API
 229         <span class="md-nav__icon md-icon"></span>
 230       </label>
 231       <nav class="md-nav" aria-label="PHP API" data-md-level="1">
 232         <label class="md-nav__title" for="__nav_2">
 233           <span class="md-nav__icon md-icon"></span>
 234           PHP API
 235         </label>
 236         <ul class="md-nav__list" data-md-scrollfix>
 237
 238
 239
 240
 241
 242     <li class="md-nav__item">
 243       <a href="../../pages/" class="md-nav__link">
 244         Pages
 245       </a>
 246     </li>
 247
 248
 249
 250
 251
 252
 253
 254     <li class="md-nav__item">
 255       <a href="../../database-objects/" class="md-nav__link">
 256         Database Objects
 257       </a>
 258     </li>
 259
 260
 261
 262
 263
 264
 265
 266     <li class="md-nav__item">
 267       <a href="../../database-access/" class="md-nav__link">
 268         Database Access
 269       </a>
 270     </li>
 271
 272
 273
 274
 275
 276
 277
 278     <li class="md-nav__item">
 279       <a href="../../exceptions/" class="md-nav__link">
 280         Exceptions
 281       </a>
 282     </li>
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293     <li class="md-nav__item md-nav__item--active md-nav__item--nested">
 294
 295
 296         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_2_5" type="checkbox" id="__nav_2_5" checked>
 297
 298       <label class="md-nav__link" for="__nav_2_5">
 299         API
 300         <span class="md-nav__icon md-icon"></span>
 301       </label>
 302       <nav class="md-nav" aria-label="API" data-md-level="2">
 303         <label class="md-nav__title" for="__nav_2_5">
 304           <span class="md-nav__icon md-icon"></span>
 305           API
 306         </label>
 307         <ul class="md-nav__list" data-md-scrollfix>
 308
 309
 310
 311
 312
 313
 314
 315
 316     <li class="md-nav__item md-nav__item--active md-nav__item--nested">
 317
 318
 319         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_2_5_1" type="checkbox" id="__nav_2_5_1" checked>
 320
 321       <label class="md-nav__link" for="__nav_2_5_1">
 322         Caches
 323         <span class="md-nav__icon md-icon"></span>
 324       </label>
 325       <nav class="md-nav" aria-label="Caches" data-md-level="3">
 326         <label class="md-nav__title" for="__nav_2_5_1">
 327           <span class="md-nav__icon md-icon"></span>
 328           Caches
 329         </label>
 330         <ul class="md-nav__list" data-md-scrollfix>
 331
 332
 333
 334
 335
 336
 337
 338     <li class="md-nav__item md-nav__item--active">
 339
 340       <input class="md-nav__toggle md-toggle" data-md-toggle="toc" type="checkbox" id="__toc">
 341
 342
 343
 344
 345         <label class="md-nav__link md-nav__link--active" for="__toc">
 346           Overview
 347           <span class="md-nav__icon md-icon"></span>
 348         </label>
 349
 350       <a href="./" class="md-nav__link md-nav__link--active">
 351         Overview
 352       </a>
 353
 354
 355 <nav class="md-nav md-nav--secondary" aria-label="Table of contents">
 356
 357
 358
 359
 360
 361     <label class="md-nav__title" for="__toc">
 362       <span class="md-nav__icon md-icon"></span>
 363       Table of contents
 364     </label>
 365     <ul class="md-nav__list" data-md-component="toc" data-md-scrollfix>
 366
 367         <li class="md-nav__item">
 368   <a href="#understanding-caching" class="md-nav__link">
 369     Understanding Caching
 370   </a>
 371
 372     <nav class="md-nav" aria-label="Understanding Caching">
 373       <ul class="md-nav__list">
 374
 375           <li class="md-nav__item">
 376   <a href="#when-to-use-a-cache" class="md-nav__link">
 377     When to Use a Cache
 378   </a>
 379
 380 </li>
 381
 382           <li class="md-nav__item">
 383   <a href="#when-not-to-use-a-cache" class="md-nav__link">
 384     When not to Use a Cache
 385   </a>
 386
 387 </li>
 388
 389       </ul>
 390     </nav>
 391
 392 </li>
 393
 394     </ul>
 395
 396 </nav>
 397
 398     </li>
 399
 400
 401
 402
 403
 404
 405
 406     <li class="md-nav__item">
 407       <a href="../caches_persistent-caches/" class="md-nav__link">
 408         Persistent Caches
 409       </a>
 410     </li>
 411
 412
 413
 414
 415
 416
 417
 418     <li class="md-nav__item">
 419       <a href="../caches_runtime-caches/" class="md-nav__link">
 420         Runtime Caches
 421       </a>
 422     </li>
 423
 424
 425
 426         </ul>
 427       </nav>
 428     </li>
 429
 430
 431
 432
 433
 434
 435
 436     <li class="md-nav__item">
 437       <a href="../comments/" class="md-nav__link">
 438         Comments
 439       </a>
 440     </li>
 441
 442
 443
 444
 445
 446
 447
 448     <li class="md-nav__item">
 449       <a href="../cronjobs/" class="md-nav__link">
 450         Cronjobs
 451       </a>
 452     </li>
 453
 454
 455
 456
 457
 458
 459
 460     <li class="md-nav__item">
 461       <a href="../events/" class="md-nav__link">
 462         Events
 463       </a>
 464     </li>
 465
 466
 467
 468
 469
 470
 471
 472
 473     <li class="md-nav__item md-nav__item--nested">
 474
 475
 476         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_2_5_5" type="checkbox" id="__nav_2_5_5" >
 477
 478       <label class="md-nav__link" for="__nav_2_5_5">
 479         Form Builder
 480         <span class="md-nav__icon md-icon"></span>
 481       </label>
 482       <nav class="md-nav" aria-label="Form Builder" data-md-level="3">
 483         <label class="md-nav__title" for="__nav_2_5_5">
 484           <span class="md-nav__icon md-icon"></span>
 485           Form Builder
 486         </label>
 487         <ul class="md-nav__list" data-md-scrollfix>
 488
 489
 490
 491
 492
 493     <li class="md-nav__item">
 494       <a href="../form_builder/overview/" class="md-nav__link">
 495         Overview
 496       </a>
 497     </li>
 498
 499
 500
 501
 502
 503
 504
 505     <li class="md-nav__item">
 506       <a href="../form_builder/structure/" class="md-nav__link">
 507         Structure
 508       </a>
 509     </li>
 510
 511
 512
 513
 514
 515
 516
 517     <li class="md-nav__item">
 518       <a href="../form_builder/form_fields/" class="md-nav__link">
 519         Fields
 520       </a>
 521     </li>
 522
 523
 524
 525
 526
 527
 528
 529     <li class="md-nav__item">
 530       <a href="../form_builder/validation_data/" class="md-nav__link">
 531         Validation and Data
 532       </a>
 533     </li>
 534
 535
 536
 537
 538
 539
 540
 541     <li class="md-nav__item">
 542       <a href="../form_builder/dependencies/" class="md-nav__link">
 543         Dependencies
 544       </a>
 545     </li>
 546
 547
 548
 549         </ul>
 550       </nav>
 551     </li>
 552
 553
 554
 555
 556
 557
 558
 559     <li class="md-nav__item">
 560       <a href="../package_installation_plugins/" class="md-nav__link">
 561         Package Installation Plugins
 562       </a>
 563     </li>
 564
 565
 566
 567
 568
 569
 570
 571     <li class="md-nav__item">
 572       <a href="../user_activity_points/" class="md-nav__link">
 573         User Activity Points
 574       </a>
 575     </li>
 576
 577
 578
 579
 580
 581
 582
 583     <li class="md-nav__item">
 584       <a href="../user_notifications/" class="md-nav__link">
 585         User Notifications
 586       </a>
 587     </li>
 588
 589
 590
 591
 592
 593
 594
 595     <li class="md-nav__item">
 596       <a href="../sitemaps/" class="md-nav__link">
 597         Sitemaps
 598       </a>
 599     </li>
 600
 601
 602
 603         </ul>
 604       </nav>
 605     </li>
 606
 607
 608
 609
 610
 611
 612
 613     <li class="md-nav__item">
 614       <a href="../../code-style/" class="md-nav__link">
 615         Code Style
 616       </a>
 617     </li>
 618
 619
 620
 621
 622
 623
 624
 625     <li class="md-nav__item">
 626       <a href="../../apps/" class="md-nav__link">
 627         Apps
 628       </a>
 629     </li>
 630
 631
 632
 633
 634
 635
 636
 637     <li class="md-nav__item">
 638       <a href="../../gdpr/" class="md-nav__link">
 639         GDPR
 640       </a>
 641     </li>
 642
 643
 644
 645         </ul>
 646       </nav>
 647     </li>
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659     <li class="md-nav__item md-nav__item--nested">
 660
 661
 662         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_3" type="checkbox" id="__nav_3" >
 663
 664       <label class="md-nav__link" for="__nav_3">
 665         Languages, Templates & CSS
 666         <span class="md-nav__icon md-icon"></span>
 667       </label>
 668       <nav class="md-nav" aria-label="Languages, Templates & CSS" data-md-level="1">
 669         <label class="md-nav__title" for="__nav_3">
 670           <span class="md-nav__icon md-icon"></span>
 671           Languages, Templates & CSS
 672         </label>
 673         <ul class="md-nav__list" data-md-scrollfix>
 674
 675
 676
 677
 678
 679     <li class="md-nav__item">
 680       <a href="../../../view/languages/" class="md-nav__link">
 681         Languages
 682       </a>
 683     </li>
 684
 685
 686
 687
 688
 689
 690
 691     <li class="md-nav__item">
 692       <a href="../../../view/templates/" class="md-nav__link">
 693         Templates
 694       </a>
 695     </li>
 696
 697
 698
 699
 700
 701
 702
 703     <li class="md-nav__item">
 704       <a href="../../../view/template-plugins/" class="md-nav__link">
 705         Template Plugins
 706       </a>
 707     </li>
 708
 709
 710
 711
 712
 713
 714
 715     <li class="md-nav__item">
 716       <a href="../../../view/css/" class="md-nav__link">
 717         CSS
 718       </a>
 719     </li>
 720
 721
 722
 723         </ul>
 724       </nav>
 725     </li>
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737     <li class="md-nav__item md-nav__item--nested">
 738
 739
 740         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_4" type="checkbox" id="__nav_4" >
 741
 742       <label class="md-nav__link" for="__nav_4">
 743         TypeScript and JavaScript API
 744         <span class="md-nav__icon md-icon"></span>
 745       </label>
 746       <nav class="md-nav" aria-label="TypeScript and JavaScript API" data-md-level="1">
 747         <label class="md-nav__title" for="__nav_4">
 748           <span class="md-nav__icon md-icon"></span>
 749           TypeScript and JavaScript API
 750         </label>
 751         <ul class="md-nav__list" data-md-scrollfix>
 752
 753
 754
 755
 756
 757     <li class="md-nav__item">
 758       <a href="../../../javascript/general-usage/" class="md-nav__link">
 759         General Usage
 760       </a>
 761     </li>
 762
 763
 764
 765
 766
 767
 768
 769     <li class="md-nav__item">
 770       <a href="../../../javascript/typescript/" class="md-nav__link">
 771         TypeScript
 772       </a>
 773     </li>
 774
 775
 776
 777
 778
 779
 780
 781
 782     <li class="md-nav__item md-nav__item--nested">
 783
 784
 785         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_4_3" type="checkbox" id="__nav_4_3" >
 786
 787       <label class="md-nav__link" for="__nav_4_3">
 788         New API
 789         <span class="md-nav__icon md-icon"></span>
 790       </label>
 791       <nav class="md-nav" aria-label="New API" data-md-level="2">
 792         <label class="md-nav__title" for="__nav_4_3">
 793           <span class="md-nav__icon md-icon"></span>
 794           New API
 795         </label>
 796         <ul class="md-nav__list" data-md-scrollfix>
 797
 798
 799
 800
 801
 802     <li class="md-nav__item">
 803       <a href="../../../javascript/new-api_writing-a-module/" class="md-nav__link">
 804         Writing a module
 805       </a>
 806     </li>
 807
 808
 809
 810
 811
 812
 813
 814     <li class="md-nav__item">
 815       <a href="../../../javascript/new-api_data-structures/" class="md-nav__link">
 816         Data Structures
 817       </a>
 818     </li>
 819
 820
 821
 822
 823
 824
 825
 826     <li class="md-nav__item">
 827       <a href="../../../javascript/new-api_core/" class="md-nav__link">
 828         Core Functions
 829       </a>
 830     </li>
 831
 832
 833
 834
 835
 836
 837
 838     <li class="md-nav__item">
 839       <a href="../../../javascript/new-api_dom/" class="md-nav__link">
 840         DOM
 841       </a>
 842     </li>
 843
 844
 845
 846
 847
 848
 849
 850     <li class="md-nav__item">
 851       <a href="../../../javascript/new-api_events/" class="md-nav__link">
 852         Event Handling
 853       </a>
 854     </li>
 855
 856
 857
 858
 859
 860
 861
 862     <li class="md-nav__item">
 863       <a href="../../../javascript/new-api_ajax/" class="md-nav__link">
 864         Ajax
 865       </a>
 866     </li>
 867
 868
 869
 870
 871
 872
 873
 874     <li class="md-nav__item">
 875       <a href="../../../javascript/new-api_dialogs/" class="md-nav__link">
 876         Dialogs
 877       </a>
 878     </li>
 879
 880
 881
 882
 883
 884
 885
 886     <li class="md-nav__item">
 887       <a href="../../../javascript/new-api_browser/" class="md-nav__link">
 888         Browser and Screen Sizes
 889       </a>
 890     </li>
 891
 892
 893
 894
 895
 896
 897
 898     <li class="md-nav__item">
 899       <a href="../../../javascript/new-api_ui/" class="md-nav__link">
 900         User Interface
 901       </a>
 902     </li>
 903
 904
 905
 906         </ul>
 907       </nav>
 908     </li>
 909
 910
 911
 912
 913
 914
 915
 916     <li class="md-nav__item">
 917       <a href="../../../javascript/legacy-api/" class="md-nav__link">
 918         Legacy API
 919       </a>
 920     </li>
 921
 922
 923
 924
 925
 926
 927
 928     <li class="md-nav__item">
 929       <a href="../../../javascript/helper-functions/" class="md-nav__link">
 930         Helper Functions
 931       </a>
 932     </li>
 933
 934
 935
 936
 937
 938
 939
 940     <li class="md-nav__item">
 941       <a href="../../../javascript/code-snippets/" class="md-nav__link">
 942         Code Snippets
 943       </a>
 944     </li>
 945
 946
 947
 948         </ul>
 949       </nav>
 950     </li>
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962     <li class="md-nav__item md-nav__item--nested">
 963
 964
 965         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_5" type="checkbox" id="__nav_5" >
 966
 967       <label class="md-nav__link" for="__nav_5">
 968         Package Components
 969         <span class="md-nav__icon md-icon"></span>
 970       </label>
 971       <nav class="md-nav" aria-label="Package Components" data-md-level="1">
 972         <label class="md-nav__title" for="__nav_5">
 973           <span class="md-nav__icon md-icon"></span>
 974           Package Components
 975         </label>
 976         <ul class="md-nav__list" data-md-scrollfix>
 977
 978
 979
 980
 981
 982     <li class="md-nav__item">
 983       <a href="../../../package/package-xml/" class="md-nav__link">
 984         package.xml
 985       </a>
 986     </li>
 987
 988
 989
 990
 991
 992
 993
 994
 995     <li class="md-nav__item md-nav__item--nested">
 996
 997
 998         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_5_2" type="checkbox" id="__nav_5_2" >
 999
1000       <label class="md-nav__link" for="__nav_5_2">
1001         PIPs
1002         <span class="md-nav__icon md-icon"></span>
1003       </label>
1004       <nav class="md-nav" aria-label="PIPs" data-md-level="2">
1005         <label class="md-nav__title" for="__nav_5_2">
1006           <span class="md-nav__icon md-icon"></span>
1007           PIPs
1008         </label>
1009         <ul class="md-nav__list" data-md-scrollfix>
1010
1011
1012
1013
1014
1015     <li class="md-nav__item">
1016       <a href="../../../package/pip/" class="md-nav__link">
1017         Overview
1018       </a>
1019     </li>
1020
1021
1022
1023
1024
1025
1026
1027     <li class="md-nav__item">
1028       <a href="../../../package/pip/acl-option/" class="md-nav__link">
1029         aclOption
1030       </a>
1031     </li>
1032
1033
1034
1035
1036
1037
1038
1039     <li class="md-nav__item">
1040       <a href="../../../package/pip/acp-menu/" class="md-nav__link">
1041         acpMenu
1042       </a>
1043     </li>
1044
1045
1046
1047
1048
1049
1050
1051     <li class="md-nav__item">
1052       <a href="../../../package/pip/acp-search-provider/" class="md-nav__link">
1053         acpSearchProvider
1054       </a>
1055     </li>
1056
1057
1058
1059
1060
1061
1062
1063     <li class="md-nav__item">
1064       <a href="../../../package/pip/acp-template/" class="md-nav__link">
1065         acpTemplate
1066       </a>
1067     </li>
1068
1069
1070
1071
1072
1073
1074
1075     <li class="md-nav__item">
1076       <a href="../../../package/pip/bbcode/" class="md-nav__link">
1077         bbcode
1078       </a>
1079     </li>
1080
1081
1082
1083
1084
1085
1086
1087     <li class="md-nav__item">
1088       <a href="../../../package/pip/box/" class="md-nav__link">
1089         box
1090       </a>
1091     </li>
1092
1093
1094
1095
1096
1097
1098
1099     <li class="md-nav__item">
1100       <a href="../../../package/pip/clipboard-action/" class="md-nav__link">
1101         clipboardAction
1102       </a>
1103     </li>
1104
1105
1106
1107
1108
1109
1110
1111     <li class="md-nav__item">
1112       <a href="../../../package/pip/core-object/" class="md-nav__link">
1113         coreObject
1114       </a>
1115     </li>
1116
1117
1118
1119
1120
1121
1122
1123     <li class="md-nav__item">
1124       <a href="../../../package/pip/cronjob/" class="md-nav__link">
1125         cronjob
1126       </a>
1127     </li>
1128
1129
1130
1131
1132
1133
1134
1135     <li class="md-nav__item">
1136       <a href="../../../package/pip/database/" class="md-nav__link">
1137         database
1138       </a>
1139     </li>
1140
1141
1142
1143
1144
1145
1146
1147     <li class="md-nav__item">
1148       <a href="../../../package/pip/event-listener/" class="md-nav__link">
1149         eventListener
1150       </a>
1151     </li>
1152
1153
1154
1155
1156
1157
1158
1159     <li class="md-nav__item">
1160       <a href="../../../package/pip/file/" class="md-nav__link">
1161         file
1162       </a>
1163     </li>
1164
1165
1166
1167
1168
1169
1170
1171     <li class="md-nav__item">
1172       <a href="../../../package/pip/language/" class="md-nav__link">
1173         language
1174       </a>
1175     </li>
1176
1177
1178
1179
1180
1181
1182
1183     <li class="md-nav__item">
1184       <a href="../../../package/pip/media-provider/" class="md-nav__link">
1185         mediaProvider
1186       </a>
1187     </li>
1188
1189
1190
1191
1192
1193
1194
1195     <li class="md-nav__item">
1196       <a href="../../../package/pip/menu/" class="md-nav__link">
1197         menu
1198       </a>
1199     </li>
1200
1201
1202
1203
1204
1205
1206
1207     <li class="md-nav__item">
1208       <a href="../../../package/pip/menu-item/" class="md-nav__link">
1209         menuItem
1210       </a>
1211     </li>
1212
1213
1214
1215
1216
1217
1218
1219     <li class="md-nav__item">
1220       <a href="../../../package/pip/object-type/" class="md-nav__link">
1221         objectType
1222       </a>
1223     </li>
1224
1225
1226
1227
1228
1229
1230
1231     <li class="md-nav__item">
1232       <a href="../../../package/pip/object-type-definition/" class="md-nav__link">
1233         objectTypeDefinition
1234       </a>
1235     </li>
1236
1237
1238
1239
1240
1241
1242
1243     <li class="md-nav__item">
1244       <a href="../../../package/pip/option/" class="md-nav__link">
1245         option
1246       </a>
1247     </li>
1248
1249
1250
1251
1252
1253
1254
1255     <li class="md-nav__item">
1256       <a href="../../../package/pip/page/" class="md-nav__link">
1257         page
1258       </a>
1259     </li>
1260
1261
1262
1263
1264
1265
1266
1267     <li class="md-nav__item">
1268       <a href="../../../package/pip/pip/" class="md-nav__link">
1269         pip
1270       </a>
1271     </li>
1272
1273
1274
1275
1276
1277
1278
1279     <li class="md-nav__item">
1280       <a href="../../../package/pip/script/" class="md-nav__link">
1281         script
1282       </a>
1283     </li>
1284
1285
1286
1287
1288
1289
1290
1291     <li class="md-nav__item">
1292       <a href="../../../package/pip/smiley/" class="md-nav__link">
1293         smiley
1294       </a>
1295     </li>
1296
1297
1298
1299
1300
1301
1302
1303     <li class="md-nav__item">
1304       <a href="../../../package/pip/sql/" class="md-nav__link">
1305         sql
1306       </a>
1307     </li>
1308
1309
1310
1311
1312
1313
1314
1315     <li class="md-nav__item">
1316       <a href="../../../package/pip/style/" class="md-nav__link">
1317         style
1318       </a>
1319     </li>
1320
1321
1322
1323
1324
1325
1326
1327     <li class="md-nav__item">
1328       <a href="../../../package/pip/template/" class="md-nav__link">
1329         template
1330       </a>
1331     </li>
1332
1333
1334
1335
1336
1337
1338
1339     <li class="md-nav__item">
1340       <a href="../../../package/pip/template-listener/" class="md-nav__link">
1341         templateListener
1342       </a>
1343     </li>
1344
1345
1346
1347
1348
1349
1350
1351     <li class="md-nav__item">
1352       <a href="../../../package/pip/user-group-option/" class="md-nav__link">
1353         userGroupOption
1354       </a>
1355     </li>
1356
1357
1358
1359
1360
1361
1362
1363     <li class="md-nav__item">
1364       <a href="../../../package/pip/user-menu/" class="md-nav__link">
1365         userMenu
1366       </a>
1367     </li>
1368
1369
1370
1371
1372
1373
1374
1375     <li class="md-nav__item">
1376       <a href="../../../package/pip/user-notification-event/" class="md-nav__link">
1377         userNotificationEvent
1378       </a>
1379     </li>
1380
1381
1382
1383
1384
1385
1386
1387     <li class="md-nav__item">
1388       <a href="../../../package/pip/user-option/" class="md-nav__link">
1389         userOption
1390       </a>
1391     </li>
1392
1393
1394
1395
1396
1397
1398
1399     <li class="md-nav__item">
1400       <a href="../../../package/pip/user-profile-menu/" class="md-nav__link">
1401         userProfileMenu
1402       </a>
1403     </li>
1404
1405
1406
1407         </ul>
1408       </nav>
1409     </li>
1410
1411
1412
1413
1414
1415
1416
1417     <li class="md-nav__item">
1418       <a href="../../../package/database-php-api/" class="md-nav__link">
1419         Database PHP API
1420       </a>
1421     </li>
1422
1423
1424
1425         </ul>
1426       </nav>
1427     </li>
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439     <li class="md-nav__item md-nav__item--nested">
1440
1441
1442         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_6" type="checkbox" id="__nav_6" >
1443
1444       <label class="md-nav__link" for="__nav_6">
1445         Migration
1446         <span class="md-nav__icon md-icon"></span>
1447       </label>
1448       <nav class="md-nav" aria-label="Migration" data-md-level="1">
1449         <label class="md-nav__title" for="__nav_6">
1450           <span class="md-nav__icon md-icon"></span>
1451           Migration
1452         </label>
1453         <ul class="md-nav__list" data-md-scrollfix>
1454
1455
1456
1457
1458
1459
1460     <li class="md-nav__item md-nav__item--nested">
1461
1462
1463         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_6_1" type="checkbox" id="__nav_6_1" >
1464
1465       <label class="md-nav__link" for="__nav_6_1">
1466         Migrating from WSC 5.3
1467         <span class="md-nav__icon md-icon"></span>
1468       </label>
1469       <nav class="md-nav" aria-label="Migrating from WSC 5.3" data-md-level="2">
1470         <label class="md-nav__title" for="__nav_6_1">
1471           <span class="md-nav__icon md-icon"></span>
1472           Migrating from WSC 5.3
1473         </label>
1474         <ul class="md-nav__list" data-md-scrollfix>
1475
1476
1477
1478
1479
1480     <li class="md-nav__item">
1481       <a href="../../../migration/wsc53/php/" class="md-nav__link">
1482         PHP API
1483       </a>
1484     </li>
1485
1486
1487
1488
1489
1490
1491
1492     <li class="md-nav__item">
1493       <a href="../../../migration/wsc53/session/" class="md-nav__link">
1494         Session Handling and Authentication
1495       </a>
1496     </li>
1497
1498
1499
1500
1501
1502
1503
1504     <li class="md-nav__item">
1505       <a href="../../../migration/wsc53/javascript/" class="md-nav__link">
1506         TypeScript and JavaScript
1507       </a>
1508     </li>
1509
1510
1511
1512
1513
1514
1515
1516     <li class="md-nav__item">
1517       <a href="../../../migration/wsc53/templates/" class="md-nav__link">
1518         Templates
1519       </a>
1520     </li>
1521
1522
1523
1524
1525
1526
1527
1528     <li class="md-nav__item">
1529       <a href="../../../migration/wsc53/libraries/" class="md-nav__link">
1530         Third Party Libraries
1531       </a>
1532     </li>
1533
1534
1535
1536         </ul>
1537       </nav>
1538     </li>
1539
1540
1541
1542
1543
1544
1545
1546
1547     <li class="md-nav__item md-nav__item--nested">
1548
1549
1550         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_6_2" type="checkbox" id="__nav_6_2" >
1551
1552       <label class="md-nav__link" for="__nav_6_2">
1553         Migrating from WSC 5.2
1554         <span class="md-nav__icon md-icon"></span>
1555       </label>
1556       <nav class="md-nav" aria-label="Migrating from WSC 5.2" data-md-level="2">
1557         <label class="md-nav__title" for="__nav_6_2">
1558           <span class="md-nav__icon md-icon"></span>
1559           Migrating from WSC 5.2
1560         </label>
1561         <ul class="md-nav__list" data-md-scrollfix>
1562
1563
1564
1565
1566
1567     <li class="md-nav__item">
1568       <a href="../../../migration/wsc52/php/" class="md-nav__link">
1569         PHP API
1570       </a>
1571     </li>
1572
1573
1574
1575
1576
1577
1578
1579     <li class="md-nav__item">
1580       <a href="../../../migration/wsc52/templates/" class="md-nav__link">
1581         Templates and Languages
1582       </a>
1583     </li>
1584
1585
1586
1587
1588
1589
1590
1591     <li class="md-nav__item">
1592       <a href="../../../migration/wsc52/libraries/" class="md-nav__link">
1593         Third Party Libraries
1594       </a>
1595     </li>
1596
1597
1598
1599         </ul>
1600       </nav>
1601     </li>
1602
1603
1604
1605
1606
1607
1608
1609
1610     <li class="md-nav__item md-nav__item--nested">
1611
1612
1613         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_6_3" type="checkbox" id="__nav_6_3" >
1614
1615       <label class="md-nav__link" for="__nav_6_3">
1616         Migrating from WSC 3.1
1617         <span class="md-nav__icon md-icon"></span>
1618       </label>
1619       <nav class="md-nav" aria-label="Migrating from WSC 3.1" data-md-level="2">
1620         <label class="md-nav__title" for="__nav_6_3">
1621           <span class="md-nav__icon md-icon"></span>
1622           Migrating from WSC 3.1
1623         </label>
1624         <ul class="md-nav__list" data-md-scrollfix>
1625
1626
1627
1628
1629
1630     <li class="md-nav__item">
1631       <a href="../../../migration/wsc31/php/" class="md-nav__link">
1632         PHP API
1633       </a>
1634     </li>
1635
1636
1637
1638         </ul>
1639       </nav>
1640     </li>
1641
1642
1643
1644
1645
1646
1647
1648
1649     <li class="md-nav__item md-nav__item--nested">
1650
1651
1652         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_6_4" type="checkbox" id="__nav_6_4" >
1653
1654       <label class="md-nav__link" for="__nav_6_4">
1655         Migrating from WSC 3.0
1656         <span class="md-nav__icon md-icon"></span>
1657       </label>
1658       <nav class="md-nav" aria-label="Migrating from WSC 3.0" data-md-level="2">
1659         <label class="md-nav__title" for="__nav_6_4">
1660           <span class="md-nav__icon md-icon"></span>
1661           Migrating from WSC 3.0
1662         </label>
1663         <ul class="md-nav__list" data-md-scrollfix>
1664
1665
1666
1667
1668
1669     <li class="md-nav__item">
1670       <a href="../../../migration/wsc30/php/" class="md-nav__link">
1671         PHP API
1672       </a>
1673     </li>
1674
1675
1676
1677
1678
1679
1680
1681     <li class="md-nav__item">
1682       <a href="../../../migration/wsc30/javascript/" class="md-nav__link">
1683         JavaScript API
1684       </a>
1685     </li>
1686
1687
1688
1689
1690
1691
1692
1693     <li class="md-nav__item">
1694       <a href="../../../migration/wsc30/templates/" class="md-nav__link">
1695         Templates
1696       </a>
1697     </li>
1698
1699
1700
1701
1702
1703
1704
1705     <li class="md-nav__item">
1706       <a href="../../../migration/wsc30/css/" class="md-nav__link">
1707         CSS
1708       </a>
1709     </li>
1710
1711
1712
1713
1714
1715
1716
1717     <li class="md-nav__item">
1718       <a href="../../../migration/wsc30/package/" class="md-nav__link">
1719         Package Components
1720       </a>
1721     </li>
1722
1723
1724
1725         </ul>
1726       </nav>
1727     </li>
1728
1729
1730
1731
1732
1733
1734
1735
1736     <li class="md-nav__item md-nav__item--nested">
1737
1738
1739         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_6_5" type="checkbox" id="__nav_6_5" >
1740
1741       <label class="md-nav__link" for="__nav_6_5">
1742         Migrating from WCF 2.1
1743         <span class="md-nav__icon md-icon"></span>
1744       </label>
1745       <nav class="md-nav" aria-label="Migrating from WCF 2.1" data-md-level="2">
1746         <label class="md-nav__title" for="__nav_6_5">
1747           <span class="md-nav__icon md-icon"></span>
1748           Migrating from WCF 2.1
1749         </label>
1750         <ul class="md-nav__list" data-md-scrollfix>
1751
1752
1753
1754
1755
1756     <li class="md-nav__item">
1757       <a href="../../../migration/wcf21/php/" class="md-nav__link">
1758         PHP API
1759       </a>
1760     </li>
1761
1762
1763
1764
1765
1766
1767
1768     <li class="md-nav__item">
1769       <a href="../../../migration/wcf21/templates/" class="md-nav__link">
1770         Templates
1771       </a>
1772     </li>
1773
1774
1775
1776
1777
1778
1779
1780     <li class="md-nav__item">
1781       <a href="../../../migration/wcf21/css/" class="md-nav__link">
1782         CSS
1783       </a>
1784     </li>
1785
1786
1787
1788
1789
1790
1791
1792     <li class="md-nav__item">
1793       <a href="../../../migration/wcf21/package/" class="md-nav__link">
1794         Package Components
1795       </a>
1796     </li>
1797
1798
1799
1800         </ul>
1801       </nav>
1802     </li>
1803
1804
1805
1806         </ul>
1807       </nav>
1808     </li>
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820     <li class="md-nav__item md-nav__item--nested">
1821
1822
1823         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_7" type="checkbox" id="__nav_7" >
1824
1825       <label class="md-nav__link" for="__nav_7">
1826         Tutorials
1827         <span class="md-nav__icon md-icon"></span>
1828       </label>
1829       <nav class="md-nav" aria-label="Tutorials" data-md-level="1">
1830         <label class="md-nav__title" for="__nav_7">
1831           <span class="md-nav__icon md-icon"></span>
1832           Tutorials
1833         </label>
1834         <ul class="md-nav__list" data-md-scrollfix>
1835
1836
1837
1838
1839
1840
1841     <li class="md-nav__item md-nav__item--nested">
1842
1843
1844         <input class="md-nav__toggle md-toggle" data-md-toggle="__nav_7_1" type="checkbox" id="__nav_7_1" >
1845
1846       <label class="md-nav__link" for="__nav_7_1">
1847         Tutorial Series
1848         <span class="md-nav__icon md-icon"></span>
1849       </label>
1850       <nav class="md-nav" aria-label="Tutorial Series" data-md-level="2">
1851         <label class="md-nav__title" for="__nav_7_1">
1852           <span class="md-nav__icon md-icon"></span>
1853           Tutorial Series
1854         </label>
1855         <ul class="md-nav__list" data-md-scrollfix>
1856
1857
1858
1859
1860
1861     <li class="md-nav__item">
1862       <a href="../../../tutorial/series/overview/" class="md-nav__link">
1863         Overview
1864       </a>
1865     </li>
1866
1867
1868
1869
1870
1871
1872
1873     <li class="md-nav__item">
1874       <a href="../../../tutorial/series/part_1/" class="md-nav__link">
1875         Part 1
1876       </a>
1877     </li>
1878
1879
1880
1881
1882
1883
1884
1885     <li class="md-nav__item">
1886       <a href="../../../tutorial/series/part_2/" class="md-nav__link">
1887         Part 2
1888       </a>
1889     </li>
1890
1891
1892
1893
1894
1895
1896
1897     <li class="md-nav__item">
1898       <a href="../../../tutorial/series/part_3/" class="md-nav__link">
1899         Part 3
1900       </a>
1901     </li>
1902
1903
1904
1905         </ul>
1906       </nav>
1907     </li>
1908
1909
1910
1911         </ul>
1912       </nav>
1913     </li>
1914
1915
1916
1917   </ul>
1918 </nav>
1919                   </div>
1920                 </div>
1921               </div>
1922
1923
1924
1925               <div class="md-sidebar md-sidebar--secondary" data-md-component="sidebar" data-md-type="toc" >
1926                 <div class="md-sidebar__scrollwrap">
1927                   <div class="md-sidebar__inner">
1928
1929 <nav class="md-nav md-nav--secondary" aria-label="Table of contents">
1930
1931
1932
1933
1934
1935     <label class="md-nav__title" for="__toc">
1936       <span class="md-nav__icon md-icon"></span>
1937       Table of contents
1938     </label>
1939     <ul class="md-nav__list" data-md-component="toc" data-md-scrollfix>
1940
1941         <li class="md-nav__item">
1942   <a href="#understanding-caching" class="md-nav__link">
1943     Understanding Caching
1944   </a>
1945
1946     <nav class="md-nav" aria-label="Understanding Caching">
1947       <ul class="md-nav__list">
1948
1949           <li class="md-nav__item">
1950   <a href="#when-to-use-a-cache" class="md-nav__link">
1951     When to Use a Cache
1952   </a>
1953
1954 </li>
1955
1956           <li class="md-nav__item">
1957   <a href="#when-not-to-use-a-cache" class="md-nav__link">
1958     When not to Use a Cache
1959   </a>
1960
1961 </li>
1962
1963       </ul>
1964     </nav>
1965
1966 </li>
1967
1968     </ul>
1969
1970 </nav>
1971                   </div>
1972                 </div>
1973               </div>
1974
1975
1976           <div class="md-content" data-md-component="content">
1977             <article class="md-content__inner md-typeset">
1978
1979
1980                   <a href="https://github.com/WoltLab/docs.woltlab.com/edit/5.4/docs/php/api/caches.md" title="Edit this page" class="md-content__button md-icon">
1981                     <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M20.71 7.04c.39-.39.39-1.04 0-1.41l-2.34-2.34c-.37-.39-1.02-.39-1.41 0l-1.84 1.83 3.75 3.75M3 17.25V21h3.75L17.81 9.93l-3.75-3.75L3 17.25z"/></svg>
1982                   </a>
1983
1984
1985                 <h1 id="caches">Caches<a class="headerlink" href="#caches" title="Permanent link">#</a></h1>
1986 <p>WoltLab Suite offers two distinct types of caches:</p>
1987 <ol>
1988 <li><a href="../caches_persistent-caches/">Persistent caches</a> created by cache builders whose data can be stored using different cache sources.</li>
1989 <li><a href="../caches_runtime-caches/">Runtime caches</a> store objects for the duration of a single request.</li>
1990 </ol>
1991 <h2 id="understanding-caching">Understanding Caching<a class="headerlink" href="#understanding-caching" title="Permanent link">#</a></h2>
1992 <p>Every so often, plugins make use of cache builders or runtime caches to store
1993 their data, even if there is absolutely no need for them to do so. Usually, this
1994 involves a strong opinion about the total number of SQL queries on a page,
1995 including but not limited to some magic treshold numbers, which should not be
1996 exceeded for "performance reasons".</p>
1997 <p>This misconception can easily lead into thinking that SQL queries should be
1998 avoided or at least written to a cache, so that it doesn't need to be executed
1999 so often. Unfortunately, this completely ignores the fact that both a single
2000 query can take down your app (e. g. full table scan on millions of rows), but
2001 10 queries using a primary key on a table with a few hundred rows will not slow
2002 down your page.</p>
2003 <p>There are some queries that should go into caches by design, but most of the
2004 cache builders weren't initially there, but instead have been added because
2005 they were required to reduce the load <em>significantly</em>. You need to understand
2006 that caches always come at a cost, even a runtime cache does! In particular,
2007 they will always consume memory that is not released over the duration of the
2008 request lifecycle and potentially even leak memory by holding references to
2009 objects and data structures that are no longer required.</p>
2010 <p>Caching should always be a solution for a problem.</p>
2011 <h3 id="when-to-use-a-cache">When to Use a Cache<a class="headerlink" href="#when-to-use-a-cache" title="Permanent link">#</a></h3>
2012 <p>It's difficult to provide a definite answer or checklist when to use a cache
2013 and why it is required at this point, because the answer is: It depends. The
2014 permission cache for user groups is a good example for a valid cache, where
2015 we can achieve significant performance improvement compared to processing this
2016 data on every request.</p>
2017 <p>Its caches are build for each permutation of user group memberships that are
2018 encountered for a page request. Building this data is an expensive process that
2019 involves both inheritance and specific rules in regards to when a value for a
2020 permission overrules another value. The added benefit of this cache is that one
2021 cache usually serves a large number of users with the same group memberships and
2022 by computing these permissions once, we can serve many different requests. Also,
2023 the permissions are rather static values that change very rarely and thus we can
2024 expect a very high cache lifetime before it gets rebuild.</p>
2025 <h3 id="when-not-to-use-a-cache">When not to Use a Cache<a class="headerlink" href="#when-not-to-use-a-cache" title="Permanent link">#</a></h3>
2026 <p>I remember, a few years ago, there was a plugin that displayed a user's character
2027 from an online video game. The character sheet not only included a list of basic
2028 statistics, but also displayed the items that this character was wearing and or
2029 holding at the time.</p>
2030 <p>The data for these items were downloaded in bulk from the game's vendor servers
2031 and stored in a persistent cache file that periodically gets renewed. There is
2032 nothing wrong with the idea of caching the data on your own server rather than
2033 requesting them everytime from the vendor's servers - not only because they
2034 imposed a limit on the number of requests per hour.</p>
2035 <p>Unfortunately, the character sheet had a sub-par performance and the users were
2036 upset by the significant loading times compared to literally every other page
2037 on the same server. The author of the plugin was working hard to resolve this
2038 issue and was evaluating all kind of methods to improve the page performance,
2039 including deep-diving into the realm of micro-optimizations to squeeze out every
2040 last bit of performance that is possible.</p>
2041 <p>The real problem was the cache file itself, it turns out that it was holding the
2042 data for several thousand items with a total file size of about 13 megabytes.
2043 It doesn't look that much at first glance, after all this isn't the '90s anymore,
2044 but unserializing a 13 megabyte array is really slow and looking up items in such
2045 a large array isn't exactly fast either.</p>
2046 <p>The solution was rather simple, the data that was fetched from the vendor's API
2047 was instead written into a separate database table. Next, the persistent cache
2048 was removed and the character sheet would now request the item data for that
2049 specific character straight from the database. Previously, the character sheet
2050 took several seconds to load and after the change it was done in a fraction of
2051 a second. Although quite extreme, this illustrates a situation where the cache
2052 file was introduced in the design process, without evaluating if the cache -
2053 at least how it was implemented - was really necessary.</p>
2054 <p>Caching should always be a solution for a problem. Not the other way around.</p>
2055
2056
2057
2058
2059 <hr>
2060 <div class="md-source-date">
2061   <small>
2062
2063       Last update: 2021-01-08
2064
2065   </small>
2066 </div>
2067
2068
2069
2070
2071
2072
2073
2074
2075             </article>
2076           </div>
2077         </div>
2078
2079       </main>
2080
2081
2082 <footer class="md-footer">
2083
2084     <nav class="md-footer__inner md-grid" aria-label="Footer">
2085
2086         <a href="../../exceptions/" class="md-footer__link md-footer__link--prev" rel="prev">
2087           <div class="md-footer__button md-icon">
2088             <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12z"/></svg>
2089           </div>
2090           <div class="md-footer__title">
2091             <div class="md-ellipsis">
2092               <span class="md-footer__direction">
2093                 Previous
2094               </span>
2095               Exceptions
2096             </div>
2097           </div>
2098         </a>
2099
2100
2101         <a href="../caches_persistent-caches/" class="md-footer__link md-footer__link--next" rel="next">
2102           <div class="md-footer__title">
2103             <div class="md-ellipsis">
2104               <span class="md-footer__direction">
2105                 Next
2106               </span>
2107               Persistent Caches
2108             </div>
2109           </div>
2110           <div class="md-footer__button md-icon">
2111             <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11H4z"/></svg>
2112           </div>
2113         </a>
2114
2115     </nav>
2116
2117   <div class="md-footer-meta md-typeset">
2118     <div class="md-footer-meta__inner md-grid">
2119       <div class="md-footer-copyright">
2120
2121           <div class="md-footer-copyright__highlight">
2122             Copyright © 2020 WoltLab GmbH
2123           </div>
2124
2125         Made with
2126         <a href="https://squidfunk.github.io/mkdocs-material/" target="_blank" rel="noopener">
2127           Material for MkDocs
2128         </a>
2129
2130       </div>
2131       <div class="md-footer-copyright">
2132         <a href="https://www.woltlab.com/legal-notice/">Legal Notice</a>
2133         <a href="https://www.woltlab.com/privacy-policy/">Privacy Policy</a>
2134 </div>
2135     </div>
2136   </div>
2137 </footer>
2138
2139     </div>
2140     <div class="md-dialog" data-md-component="dialog">
2141       <div class="md-dialog__inner md-typeset"></div>
2142     </div>
2143     <script id="__config" type="application/json">{"base": "../../..", "features": [], "translations": {"clipboard.copy": "Copy to clipboard", "clipboard.copied": "Copied to clipboard", "search.config.lang": "en", "search.config.pipeline": "trimmer, stopWordFilter", "search.config.separator": "[\\s\\-]+", "search.placeholder": "Search", "search.result.placeholder": "Type to start searching", "search.result.none": "No matching documents", "search.result.one": "1 matching document", "search.result.other": "# matching documents", "search.result.more.one": "1 more on this page", "search.result.more.other": "# more on this page", "search.result.term.missing": "Missing"}, "search": "../../../assets/javascripts/workers/search.fe42c31b.min.js", "version": {"provider": "mike"}}</script>
2144
2145
2146       <script src="../../../assets/javascripts/bundle.d892486b.min.js"></script>
2147
2148
2149   </body>
2150 </html>