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  10.   <title>Database Caching Class &mdash; CodeIgniter 3.1.11 documentation</title>
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    126. 

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    127. 

  127. <li class="toctree-l2"><a class="reference internal" href="../libraries/caching.html">Caching Driver</a></li>
    128. 

  128. <li class="toctree-l2"><a class="reference internal" href="../libraries/calendar.html">Calendaring Class</a></li>
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    142. 

  142. <li class="toctree-l2"><a class="reference internal" href="../libraries/migration.html">Migrations Class</a></li>
    143. 

  143. <li class="toctree-l2"><a class="reference internal" href="../libraries/output.html">Output Class</a></li>
    144. 

  144. <li class="toctree-l2"><a class="reference internal" href="../libraries/pagination.html">Pagination Class</a></li>
    145. 

  145. <li class="toctree-l2"><a class="reference internal" href="../libraries/parser.html">Template Parser Class</a></li>
    146. 

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    147. 

  147. <li class="toctree-l2"><a class="reference internal" href="../libraries/sessions.html">Session Library</a></li>
    148. 

  148. <li class="toctree-l2"><a class="reference internal" href="../libraries/table.html">HTML Table Class</a></li>
    149. 

  149. <li class="toctree-l2"><a class="reference internal" href="../libraries/trackback.html">Trackback Class</a></li>
    150. 

  150. <li class="toctree-l2"><a class="reference internal" href="../libraries/typography.html">Typography Class</a></li>
    151. 

  151. <li class="toctree-l2"><a class="reference internal" href="../libraries/unit_testing.html">Unit Testing Class</a></li>
    152. 

  152. <li class="toctree-l2"><a class="reference internal" href="../libraries/uri.html">URI Class</a></li>
    153. 

  153. <li class="toctree-l2"><a class="reference internal" href="../libraries/user_agent.html">User Agent Class</a></li>
    154. 

  154. <li class="toctree-l2"><a class="reference internal" href="../libraries/xmlrpc.html">XML-RPC and XML-RPC Server Classes</a></li>
    155. 

  155. <li class="toctree-l2"><a class="reference internal" href="../libraries/zip.html">Zip Encoding Class</a></li>
    156. 

  156. </ul>
    157. 

  157. </li>
    158. 

  158. </ul>
    159. 

  159. <ul class="current">
    160. 

  160. <li class="toctree-l1 current"><a class="reference internal" href="index.html">Database Reference</a><ul class="current">
    161. 

  161. <li class="toctree-l2"><a class="reference internal" href="examples.html">Quick Start: Usage Examples</a></li>
    162. 

  162. <li class="toctree-l2"><a class="reference internal" href="configuration.html">Database Configuration</a></li>
    163. 

  163. <li class="toctree-l2"><a class="reference internal" href="connecting.html">Connecting to a Database</a></li>
    164. 

  164. <li class="toctree-l2"><a class="reference internal" href="queries.html">Running Queries</a></li>
    165. 

  165. <li class="toctree-l2"><a class="reference internal" href="results.html">Generating Query Results</a></li>
    166. 

  166. <li class="toctree-l2"><a class="reference internal" href="helpers.html">Query Helper Functions</a></li>
    167. 

  167. <li class="toctree-l2"><a class="reference internal" href="query_builder.html">Query Builder Class</a></li>
    168. 

  168. <li class="toctree-l2"><a class="reference internal" href="transactions.html">Transactions</a></li>
    169. 

  169. <li class="toctree-l2"><a class="reference internal" href="metadata.html">Getting MetaData</a></li>
    170. 

  170. <li class="toctree-l2"><a class="reference internal" href="call_function.html">Custom Function Calls</a></li>
    171. 

  171. <li class="toctree-l2 current"><a class="current reference internal" href="#">Query Caching</a></li>
    172. 

  172. <li class="toctree-l2"><a class="reference internal" href="forge.html">Database Manipulation with Database Forge</a></li>
    173. 

  173. <li class="toctree-l2"><a class="reference internal" href="utilities.html">Database Utilities Class</a></li>
    174. 

  174. <li class="toctree-l2"><a class="reference internal" href="db_driver_reference.html">Database Driver Reference</a></li>
    175. 

  175. </ul>
    176. 

  176. </li>
    177. 

  177. </ul>
    178. 

  178. <ul>
    179. 

  179. <li class="toctree-l1"><a class="reference internal" href="../helpers/index.html">Helpers</a><ul>
    180. 

  180. <li class="toctree-l2"><a class="reference internal" href="../helpers/array_helper.html">Array Helper</a></li>
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    183. 

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    184. 

  184. <li class="toctree-l2"><a class="reference internal" href="../helpers/directory_helper.html">Directory Helper</a></li>
    185. 

  185. <li class="toctree-l2"><a class="reference internal" href="../helpers/download_helper.html">Download Helper</a></li>
    186. 

  186. <li class="toctree-l2"><a class="reference internal" href="../helpers/email_helper.html">Email Helper</a></li>
    187. 

  187. <li class="toctree-l2"><a class="reference internal" href="../helpers/file_helper.html">File Helper</a></li>
    188. 

  188. <li class="toctree-l2"><a class="reference internal" href="../helpers/form_helper.html">Form Helper</a></li>
    189. 

  189. <li class="toctree-l2"><a class="reference internal" href="../helpers/html_helper.html">HTML Helper</a></li>
    190. 

  190. <li class="toctree-l2"><a class="reference internal" href="../helpers/inflector_helper.html">Inflector Helper</a></li>
    191. 

  191. <li class="toctree-l2"><a class="reference internal" href="../helpers/language_helper.html">Language Helper</a></li>
    192. 

  192. <li class="toctree-l2"><a class="reference internal" href="../helpers/number_helper.html">Number Helper</a></li>
    193. 

  193. <li class="toctree-l2"><a class="reference internal" href="../helpers/path_helper.html">Path Helper</a></li>
    194. 

  194. <li class="toctree-l2"><a class="reference internal" href="../helpers/security_helper.html">Security Helper</a></li>
    195. 

  195. <li class="toctree-l2"><a class="reference internal" href="../helpers/smiley_helper.html">Smiley Helper</a></li>
    196. 

  196. <li class="toctree-l2"><a class="reference internal" href="../helpers/string_helper.html">String Helper</a></li>
    197. 

  197. <li class="toctree-l2"><a class="reference internal" href="../helpers/text_helper.html">Text Helper</a></li>
    198. 

  198. <li class="toctree-l2"><a class="reference internal" href="../helpers/typography_helper.html">Typography Helper</a></li>
    199. 

  199. <li class="toctree-l2"><a class="reference internal" href="../helpers/url_helper.html">URL Helper</a></li>
    200. 

  200. <li class="toctree-l2"><a class="reference internal" href="../helpers/xml_helper.html">XML Helper</a></li>
    201. 

  201. </ul>
    202. 

  202. </li>
    203. 

  203. </ul>
    204. 

  204. 

  205.       </div>
    206. 

  206.     
    207. 

  207.       
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  208.   </div>
    209. 

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  210. <div id="nav2">
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  211.   <a href="#" id="openToc">
    212. 

  212.     <img src="data:image/jpeg;base64,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" title="Toggle Table of Contents" alt="Toggle Table of Contents" />
    213. 

  213.   </a>
    214. 

  214. </div>
    215. 

  215. 

  216.   <div class="wy-grid-for-nav">
    217. 

  217. 

  218.     
    219. 

  219.     <nav data-toggle="wy-nav-shift" class="wy-nav-side">
    220. 

  220.       <div class="wy-side-nav-search">
    221. 

  221.         
    222. 

  222.           <a href="../index.html" class="fa fa-home"> CodeIgniter</a>
    223. 

  223.         
    224. 

  224.         
    225. 

  225. <div role="search">
    226. 

  226.   <form id="rtd-search-form" class="wy-form" action="../search.html" method="get">
    227. 

  227.     <input type="text" name="q" placeholder="Search docs" />
    228. 

  228.     <input type="hidden" name="check_keywords" value="yes" />
    229. 

  229.     <input type="hidden" name="area" value="default" />
    230. 

  230.   </form>
    231. 

  231. </div>
    232. 

  232.       </div>
    233. 

  233. 

  234.       <div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
    235. 

  235.         
    236. 

  236.           
    237. 

  237.           
    238. 

  238.               <ul>
    239. 

  239. <li class="toctree-l1"><a class="reference internal" href="../general/welcome.html">Welcome to CodeIgniter</a></li>
    240. 

  240. </ul>
    241. 

  241. <ul>
    242. 

  242. <li class="toctree-l1"><a class="reference internal" href="../installation/index.html">Installation Instructions</a><ul>
    243. 

  243. <li class="toctree-l2"><a class="reference internal" href="../installation/downloads.html">Downloading CodeIgniter</a></li>
    244. 

  244. <li class="toctree-l2"><a class="reference internal" href="../installation/index.html">Installation Instructions</a></li>
    245. 

  245. <li class="toctree-l2"><a class="reference internal" href="../installation/upgrading.html">Upgrading From a Previous Version</a></li>
    246. 

  246. <li class="toctree-l2"><a class="reference internal" href="../installation/troubleshooting.html">Troubleshooting</a></li>
    247. 

  247. </ul>
    248. 

  248. </li>
    249. 

  249. </ul>
    250. 

  250. <ul>
    251. 

  251. <li class="toctree-l1"><a class="reference internal" href="../overview/index.html">CodeIgniter Overview</a><ul>
    252. 

  252. <li class="toctree-l2"><a class="reference internal" href="../overview/getting_started.html">Getting Started</a></li>
    253. 

  253. <li class="toctree-l2"><a class="reference internal" href="../overview/at_a_glance.html">CodeIgniter at a Glance</a></li>
    254. 

  254. <li class="toctree-l2"><a class="reference internal" href="../overview/features.html">Supported Features</a></li>
    255. 

  255. <li class="toctree-l2"><a class="reference internal" href="../overview/appflow.html">Application Flow Chart</a></li>
    256. 

  256. <li class="toctree-l2"><a class="reference internal" href="../overview/mvc.html">Model-View-Controller</a></li>
    257. 

  257. <li class="toctree-l2"><a class="reference internal" href="../overview/goals.html">Architectural Goals</a></li>
    258. 

  258. </ul>
    259. 

  259. </li>
    260. 

  260. </ul>
    261. 

  261. <ul>
    262. 

  262. <li class="toctree-l1"><a class="reference internal" href="../tutorial/index.html">Tutorial</a><ul>
    263. 

  263. <li class="toctree-l2"><a class="reference internal" href="../tutorial/static_pages.html">Static pages</a></li>
    264. 

  264. <li class="toctree-l2"><a class="reference internal" href="../tutorial/news_section.html">News section</a></li>
    265. 

  265. <li class="toctree-l2"><a class="reference internal" href="../tutorial/create_news_items.html">Create news items</a></li>
    266. 

  266. <li class="toctree-l2"><a class="reference internal" href="../tutorial/conclusion.html">Conclusion</a></li>
    267. 

  267. </ul>
    268. 

  268. </li>
    269. 

  269. </ul>
    270. 

  270. <ul>
    271. 

  271. <li class="toctree-l1"><a class="reference internal" href="../contributing/index.html">Contributing to CodeIgniter</a><ul>
    272. 

  272. <li class="toctree-l2"><a class="reference internal" href="../documentation/index.html">Writing CodeIgniter Documentation</a></li>
    273. 

  273. <li class="toctree-l2"><a class="reference internal" href="../DCO.html">Developer’s Certificate of Origin 1.1</a></li>
    274. 

  274. </ul>
    275. 

  275. </li>
    276. 

  276. </ul>
    277. 

  277. <ul>
    278. 

  278. <li class="toctree-l1"><a class="reference internal" href="../general/index.html">General Topics</a><ul>
    279. 

  279. <li class="toctree-l2"><a class="reference internal" href="../general/urls.html">CodeIgniter URLs</a></li>
    280. 

  280. <li class="toctree-l2"><a class="reference internal" href="../general/controllers.html">Controllers</a></li>
    281. 

  281. <li class="toctree-l2"><a class="reference internal" href="../general/reserved_names.html">Reserved Names</a></li>
    282. 

  282. <li class="toctree-l2"><a class="reference internal" href="../general/views.html">Views</a></li>
    283. 

  283. <li class="toctree-l2"><a class="reference internal" href="../general/models.html">Models</a></li>
    284. 

  284. <li class="toctree-l2"><a class="reference internal" href="../general/helpers.html">Helpers</a></li>
    285. 

  285. <li class="toctree-l2"><a class="reference internal" href="../general/libraries.html">Using CodeIgniter Libraries</a></li>
    286. 

  286. <li class="toctree-l2"><a class="reference internal" href="../general/creating_libraries.html">Creating Libraries</a></li>
    287. 

  287. <li class="toctree-l2"><a class="reference internal" href="../general/drivers.html">Using CodeIgniter Drivers</a></li>
    288. 

  288. <li class="toctree-l2"><a class="reference internal" href="../general/creating_drivers.html">Creating Drivers</a></li>
    289. 

  289. <li class="toctree-l2"><a class="reference internal" href="../general/core_classes.html">Creating Core System Classes</a></li>
    290. 

  290. <li class="toctree-l2"><a class="reference internal" href="../general/ancillary_classes.html">Creating Ancillary Classes</a></li>
    291. 

  291. <li class="toctree-l2"><a class="reference internal" href="../general/hooks.html">Hooks - Extending the Framework Core</a></li>
    292. 

  292. <li class="toctree-l2"><a class="reference internal" href="../general/autoloader.html">Auto-loading Resources</a></li>
    293. 

  293. <li class="toctree-l2"><a class="reference internal" href="../general/common_functions.html">Common Functions</a></li>
    294. 

  294. <li class="toctree-l2"><a class="reference internal" href="../general/compatibility_functions.html">Compatibility Functions</a></li>
    295. 

  295. <li class="toctree-l2"><a class="reference internal" href="../general/routing.html">URI Routing</a></li>
    296. 

  296. <li class="toctree-l2"><a class="reference internal" href="../general/errors.html">Error Handling</a></li>
    297. 

  297. <li class="toctree-l2"><a class="reference internal" href="../general/caching.html">Caching</a></li>
    298. 

  298. <li class="toctree-l2"><a class="reference internal" href="../general/profiling.html">Profiling Your Application</a></li>
    299. 

  299. <li class="toctree-l2"><a class="reference internal" href="../general/cli.html">Running via the CLI</a></li>
    300. 

  300. <li class="toctree-l2"><a class="reference internal" href="../general/managing_apps.html">Managing your Applications</a></li>
    301. 

  301. <li class="toctree-l2"><a class="reference internal" href="../general/environments.html">Handling Multiple Environments</a></li>
    302. 

  302. <li class="toctree-l2"><a class="reference internal" href="../general/alternative_php.html">Alternate PHP Syntax for View Files</a></li>
    303. 

  303. <li class="toctree-l2"><a class="reference internal" href="../general/security.html">Security</a></li>
    304. 

  304. <li class="toctree-l2"><a class="reference internal" href="../general/styleguide.html">PHP Style Guide</a></li>
    305. 

  305. </ul>
    306. 

  306. </li>
    307. 

  307. </ul>
    308. 

  308. <ul>
    309. 

  309. <li class="toctree-l1"><a class="reference internal" href="../libraries/index.html">Libraries</a><ul>
    310. 

  310. <li class="toctree-l2"><a class="reference internal" href="../libraries/benchmark.html">Benchmarking Class</a></li>
    311. 

  311. <li class="toctree-l2"><a class="reference internal" href="../libraries/caching.html">Caching Driver</a></li>
    312. 

  312. <li class="toctree-l2"><a class="reference internal" href="../libraries/calendar.html">Calendaring Class</a></li>
    313. 

  313. <li class="toctree-l2"><a class="reference internal" href="../libraries/cart.html">Shopping Cart Class</a></li>
    314. 

  314. <li class="toctree-l2"><a class="reference internal" href="../libraries/config.html">Config Class</a></li>
    315. 

  315. <li class="toctree-l2"><a class="reference internal" href="../libraries/email.html">Email Class</a></li>
    316. 

  316. <li class="toctree-l2"><a class="reference internal" href="../libraries/encrypt.html">Encrypt Class</a></li>
    317. 

  317. <li class="toctree-l2"><a class="reference internal" href="../libraries/encryption.html">Encryption Library</a></li>
    318. 

  318. <li class="toctree-l2"><a class="reference internal" href="../libraries/file_uploading.html">File Uploading Class</a></li>
    319. 

  319. <li class="toctree-l2"><a class="reference internal" href="../libraries/form_validation.html">Form Validation</a></li>
    320. 

  320. <li class="toctree-l2"><a class="reference internal" href="../libraries/ftp.html">FTP Class</a></li>
    321. 

  321. <li class="toctree-l2"><a class="reference internal" href="../libraries/image_lib.html">Image Manipulation Class</a></li>
    322. 

  322. <li class="toctree-l2"><a class="reference internal" href="../libraries/input.html">Input Class</a></li>
    323. 

  323. <li class="toctree-l2"><a class="reference internal" href="../libraries/javascript.html">Javascript Class</a></li>
    324. 

  324. <li class="toctree-l2"><a class="reference internal" href="../libraries/language.html">Language Class</a></li>
    325. 

  325. <li class="toctree-l2"><a class="reference internal" href="../libraries/loader.html">Loader Class</a></li>
    326. 

  326. <li class="toctree-l2"><a class="reference internal" href="../libraries/migration.html">Migrations Class</a></li>
    327. 

  327. <li class="toctree-l2"><a class="reference internal" href="../libraries/output.html">Output Class</a></li>
    328. 

  328. <li class="toctree-l2"><a class="reference internal" href="../libraries/pagination.html">Pagination Class</a></li>
    329. 

  329. <li class="toctree-l2"><a class="reference internal" href="../libraries/parser.html">Template Parser Class</a></li>
    330. 

  330. <li class="toctree-l2"><a class="reference internal" href="../libraries/security.html">Security Class</a></li>
    331. 

  331. <li class="toctree-l2"><a class="reference internal" href="../libraries/sessions.html">Session Library</a></li>
    332. 

  332. <li class="toctree-l2"><a class="reference internal" href="../libraries/table.html">HTML Table Class</a></li>
    333. 

  333. <li class="toctree-l2"><a class="reference internal" href="../libraries/trackback.html">Trackback Class</a></li>
    334. 

  334. <li class="toctree-l2"><a class="reference internal" href="../libraries/typography.html">Typography Class</a></li>
    335. 

  335. <li class="toctree-l2"><a class="reference internal" href="../libraries/unit_testing.html">Unit Testing Class</a></li>
    336. 

  336. <li class="toctree-l2"><a class="reference internal" href="../libraries/uri.html">URI Class</a></li>
    337. 

  337. <li class="toctree-l2"><a class="reference internal" href="../libraries/user_agent.html">User Agent Class</a></li>
    338. 

  338. <li class="toctree-l2"><a class="reference internal" href="../libraries/xmlrpc.html">XML-RPC and XML-RPC Server Classes</a></li>
    339. 

  339. <li class="toctree-l2"><a class="reference internal" href="../libraries/zip.html">Zip Encoding Class</a></li>
    340. 

  340. </ul>
    341. 

  341. </li>
    342. 

  342. </ul>
    343. 

  343. <ul class="current">
    344. 

  344. <li class="toctree-l1 current"><a class="reference internal" href="index.html">Database Reference</a><ul class="current">
    345. 

  345. <li class="toctree-l2"><a class="reference internal" href="examples.html">Quick Start: Usage Examples</a></li>
    346. 

  346. <li class="toctree-l2"><a class="reference internal" href="configuration.html">Database Configuration</a></li>
    347. 

  347. <li class="toctree-l2"><a class="reference internal" href="connecting.html">Connecting to a Database</a></li>
    348. 

  348. <li class="toctree-l2"><a class="reference internal" href="queries.html">Running Queries</a></li>
    349. 

  349. <li class="toctree-l2"><a class="reference internal" href="results.html">Generating Query Results</a></li>
    350. 

  350. <li class="toctree-l2"><a class="reference internal" href="helpers.html">Query Helper Functions</a></li>
    351. 

  351. <li class="toctree-l2"><a class="reference internal" href="query_builder.html">Query Builder Class</a></li>
    352. 

  352. <li class="toctree-l2"><a class="reference internal" href="transactions.html">Transactions</a></li>
    353. 

  353. <li class="toctree-l2"><a class="reference internal" href="metadata.html">Getting MetaData</a></li>
    354. 

  354. <li class="toctree-l2"><a class="reference internal" href="call_function.html">Custom Function Calls</a></li>
    355. 

  355. <li class="toctree-l2 current"><a class="current reference internal" href="#">Query Caching</a></li>
    356. 

  356. <li class="toctree-l2"><a class="reference internal" href="forge.html">Database Manipulation with Database Forge</a></li>
    357. 

  357. <li class="toctree-l2"><a class="reference internal" href="utilities.html">Database Utilities Class</a></li>
    358. 

  358. <li class="toctree-l2"><a class="reference internal" href="db_driver_reference.html">Database Driver Reference</a></li>
    359. 

  359. </ul>
    360. 

  360. </li>
    361. 

  361. </ul>
    362. 

  362. <ul>
    363. 

  363. <li class="toctree-l1"><a class="reference internal" href="../helpers/index.html">Helpers</a><ul>
    364. 

  364. <li class="toctree-l2"><a class="reference internal" href="../helpers/array_helper.html">Array Helper</a></li>
    365. 

  365. <li class="toctree-l2"><a class="reference internal" href="../helpers/captcha_helper.html">CAPTCHA Helper</a></li>
    366. 

  366. <li class="toctree-l2"><a class="reference internal" href="../helpers/cookie_helper.html">Cookie Helper</a></li>
    367. 

  367. <li class="toctree-l2"><a class="reference internal" href="../helpers/date_helper.html">Date Helper</a></li>
    368. 

  368. <li class="toctree-l2"><a class="reference internal" href="../helpers/directory_helper.html">Directory Helper</a></li>
    369. 

  369. <li class="toctree-l2"><a class="reference internal" href="../helpers/download_helper.html">Download Helper</a></li>
    370. 

  370. <li class="toctree-l2"><a class="reference internal" href="../helpers/email_helper.html">Email Helper</a></li>
    371. 

  371. <li class="toctree-l2"><a class="reference internal" href="../helpers/file_helper.html">File Helper</a></li>
    372. 

  372. <li class="toctree-l2"><a class="reference internal" href="../helpers/form_helper.html">Form Helper</a></li>
    373. 

  373. <li class="toctree-l2"><a class="reference internal" href="../helpers/html_helper.html">HTML Helper</a></li>
    374. 

  374. <li class="toctree-l2"><a class="reference internal" href="../helpers/inflector_helper.html">Inflector Helper</a></li>
    375. 

  375. <li class="toctree-l2"><a class="reference internal" href="../helpers/language_helper.html">Language Helper</a></li>
    376. 

  376. <li class="toctree-l2"><a class="reference internal" href="../helpers/number_helper.html">Number Helper</a></li>
    377. 

  377. <li class="toctree-l2"><a class="reference internal" href="../helpers/path_helper.html">Path Helper</a></li>
    378. 

  378. <li class="toctree-l2"><a class="reference internal" href="../helpers/security_helper.html">Security Helper</a></li>
    379. 

  379. <li class="toctree-l2"><a class="reference internal" href="../helpers/smiley_helper.html">Smiley Helper</a></li>
    380. 

  380. <li class="toctree-l2"><a class="reference internal" href="../helpers/string_helper.html">String Helper</a></li>
    381. 

  381. <li class="toctree-l2"><a class="reference internal" href="../helpers/text_helper.html">Text Helper</a></li>
    382. 

  382. <li class="toctree-l2"><a class="reference internal" href="../helpers/typography_helper.html">Typography Helper</a></li>
    383. 

  383. <li class="toctree-l2"><a class="reference internal" href="../helpers/url_helper.html">URL Helper</a></li>
    384. 

  384. <li class="toctree-l2"><a class="reference internal" href="../helpers/xml_helper.html">XML Helper</a></li>
    385. 

  385. </ul>
    386. 

  386. </li>
    387. 

  387. </ul>
    388. 

  388. 

  389.           
    390. 

  390.         
    391. 

  391.       </div>
    392. 

  392.       &nbsp;
    393. 

  393.     </nav>
    394. 

  394. 

  395.     <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">
    396. 

  396. 

  397.       
    398. 

  398.       <nav class="wy-nav-top" role="navigation" aria-label="top navigation">
    399. 

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  411.         <li><a href="index.html">Database Reference</a> &raquo;</li>
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  413.     <li>Database Caching Class</li>
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  423.           <div role="main" class="document">
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  424.             
    425. 

  425.   <div class="section" id="database-caching-class">
    426. 

  426. <h1>Database Caching Class<a class="headerlink" href="#database-caching-class" title="Permalink to this headline">¶</a></h1>
    427. 

  427. <p>The Database Caching Class permits you to cache your queries as text
    428. 

  428. files for reduced database load.</p>
    429. 

  429. <div class="admonition important">
    430. 

  430. <p class="first admonition-title">Important</p>
    431. 

  431. <p class="last">This class is initialized automatically by the database
    432. 

  432. driver when caching is enabled. Do NOT load this class manually.</p>
    433. 

  433. </div>
    434. 

  434. <div class="admonition important">
    435. 

  435. <p class="first admonition-title">Important</p>
    436. 

  436. <p class="last">Not all query result functions are available when you
    437. 

  437. use caching. Please read this page carefully.</p>
    438. 

  438. </div>
    439. 

  439. <div class="section" id="enabling-caching">
    440. 

  440. <h2>Enabling Caching<a class="headerlink" href="#enabling-caching" title="Permalink to this headline">¶</a></h2>
    441. 

  441. <p>Caching is enabled in three steps:</p>
    442. 

  442. <ul class="simple">
    443. 

  443. <li>Create a writable directory on your server where the cache files can
    444. 

  444. be stored.</li>
    445. 

  445. <li>Set the path to your cache folder in your
    446. 

  446. application/config/database.php file.</li>
    447. 

  447. <li>Enable the caching feature, either globally by setting the preference
    448. 

  448. in your application/config/database.php file, or manually as
    449. 

  449. described below.</li>
    450. 

  450. </ul>
    451. 

  451. <p>Once enabled, caching will happen automatically whenever a page is
    452. 

  452. loaded that contains database queries.</p>
    453. 

  453. </div>
    454. 

  454. <div class="section" id="how-does-caching-work">
    455. 

  455. <h2>How Does Caching Work?<a class="headerlink" href="#how-does-caching-work" title="Permalink to this headline">¶</a></h2>
    456. 

  456. <p>CodeIgniter’s query caching system happens dynamically when your pages
    457. 

  457. are viewed. When caching is enabled, the first time a web page is
    458. 

  458. loaded, the query result object will be serialized and stored in a text
    459. 

  459. file on your server. The next time the page is loaded the cache file
    460. 

  460. will be used instead of accessing your database. Your database usage can
    461. 

  461. effectively be reduced to zero for any pages that have been cached.</p>
    462. 

  462. <p>Only read-type (SELECT) queries can be cached, since these are the only
    463. 

  463. type of queries that produce a result. Write-type (INSERT, UPDATE, etc.)
    464. 

  464. queries, since they don’t generate a result, will not be cached by the
    465. 

  465. system.</p>
    466. 

  466. <p>Cache files DO NOT expire. Any queries that have been cached will remain
    467. 

  467. cached until you delete them. The caching system permits you clear
    468. 

  468. caches associated with individual pages, or you can delete the entire
    469. 

  469. collection of cache files. Typically you’ll want to use the housekeeping
    470. 

  470. functions described below to delete cache files after certain events
    471. 

  471. take place, like when you’ve added new information to your database.</p>
    472. 

  472. </div>
    473. 

  473. <div class="section" id="will-caching-improve-your-site-s-performance">
    474. 

  474. <h2>Will Caching Improve Your Site’s Performance?<a class="headerlink" href="#will-caching-improve-your-site-s-performance" title="Permalink to this headline">¶</a></h2>
    475. 

  475. <p>Getting a performance gain as a result of caching depends on many
    476. 

  476. factors. If you have a highly optimized database under very little load,
    477. 

  477. you probably won’t see a performance boost. If your database is under
    478. 

  478. heavy use you probably will see an improved response, assuming your
    479. 

  479. file-system is not overly taxed. Remember that caching simply changes
    480. 

  480. how your information is retrieved, shifting it from being a database
    481. 

  481. operation to a file-system one.</p>
    482. 

  482. <p>In some clustered server environments, for example, caching may be
    483. 

  483. detrimental since file-system operations are so intense. On single
    484. 

  484. servers in shared environments, caching will probably be beneficial.
    485. 

  485. Unfortunately there is no single answer to the question of whether you
    486. 

  486. should cache your database. It really depends on your situation.</p>
    487. 

  487. </div>
    488. 

  488. <div class="section" id="how-are-cache-files-stored">
    489. 

  489. <h2>How are Cache Files Stored?<a class="headerlink" href="#how-are-cache-files-stored" title="Permalink to this headline">¶</a></h2>
    490. 

  490. <p>CodeIgniter places the result of EACH query into its own cache file.
    491. 

  491. Sets of cache files are further organized into sub-folders corresponding
    492. 

  492. to your controller functions. To be precise, the sub-folders are named
    493. 

  493. identically to the first two segments of your URI (the controller class
    494. 

  494. name and function name).</p>
    495. 

  495. <p>For example, let’s say you have a controller called blog with a function
    496. 

  496. called comments that contains three queries. The caching system will
    497. 

  497. create a cache folder called blog+comments, into which it will write
    498. 

  498. three cache files.</p>
    499. 

  499. <p>If you use dynamic queries that change based on information in your URI
    500. 

  500. (when using pagination, for example), each instance of the query will
    501. 

  501. produce its own cache file. It’s possible, therefore, to end up with
    502. 

  502. many times more cache files than you have queries.</p>
    503. 

  503. </div>
    504. 

  504. <div class="section" id="managing-your-cache-files">
    505. 

  505. <h2>Managing your Cache Files<a class="headerlink" href="#managing-your-cache-files" title="Permalink to this headline">¶</a></h2>
    506. 

  506. <p>Since cache files do not expire, you’ll need to build deletion routines
    507. 

  507. into your application. For example, let’s say you have a blog that
    508. 

  508. allows user commenting. Whenever a new comment is submitted you’ll want
    509. 

  509. to delete the cache files associated with the controller function that
    510. 

  510. serves up your comments. You’ll find two delete functions described
    511. 

  511. below that help you clear data.</p>
    512. 

  512. </div>
    513. 

  513. <div class="section" id="not-all-database-functions-work-with-caching">
    514. 

  514. <h2>Not All Database Functions Work with Caching<a class="headerlink" href="#not-all-database-functions-work-with-caching" title="Permalink to this headline">¶</a></h2>
    515. 

  515. <p>Lastly, we need to point out that the result object that is cached is a
    516. 

  516. simplified version of the full result object. For that reason, some of
    517. 

  517. the query result functions are not available for use.</p>
    518. 

  518. <p>The following functions ARE NOT available when using a cached result
    519. 

  519. object:</p>
    520. 

  520. <ul class="simple">
    521. 

  521. <li>num_fields()</li>
    522. 

  522. <li>field_names()</li>
    523. 

  523. <li>field_data()</li>
    524. 

  524. <li>free_result()</li>
    525. 

  525. </ul>
    526. 

  526. <p>Also, the two database resources (result_id and conn_id) are not
    527. 

  527. available when caching, since result resources only pertain to run-time
    528. 

  528. operations.</p>
    529. 

  529. <div class="section" id="function-reference">
    530. 

  530. <h3>Function Reference<a class="headerlink" href="#function-reference" title="Permalink to this headline">¶</a></h3>
    531. 

  531. </div>
    532. 

  532. </div>
    533. 

  533. <div class="section" id="this-db-cache-on-this-db-cache-off">
    534. 

  534. <h2>$this-&gt;db-&gt;cache_on() / $this-&gt;db-&gt;cache_off()<a class="headerlink" href="#this-db-cache-on-this-db-cache-off" title="Permalink to this headline">¶</a></h2>
    535. 

  535. <p>Manually enables/disables caching. This can be useful if you want to
    536. 

  536. keep certain queries from being cached. Example:</p>
    537. 

  537. <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Turn caching on</span>
    538. 

  538. <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_on</span><span class="p">();</span>
    539. 

  539. <span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">query</span><span class="p">(</span><span class="s2">&quot;SELECT * FROM mytable&quot;</span><span class="p">);</span>
    540. 

  540. 

  541. <span class="c1">// Turn caching off for this one query</span>
    542. 

  542. <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_off</span><span class="p">();</span>
    543. 

  543. <span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">query</span><span class="p">(</span><span class="s2">&quot;SELECT * FROM members WHERE member_id = &#39;</span><span class="si">$current_user</span><span class="s2">&#39;&quot;</span><span class="p">);</span>
    544. 

  544. 

  545. <span class="c1">// Turn caching back on</span>
    546. 

  546. <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_on</span><span class="p">();</span>
    547. 

  547. <span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">query</span><span class="p">(</span><span class="s2">&quot;SELECT * FROM another_table&quot;</span><span class="p">);</span>
    548. 

  548. </pre></div>
    549. 

  549. </div>
    550. 

  550. </div>
    551. 

  551. <div class="section" id="this-db-cache-delete">
    552. 

  552. <h2>$this-&gt;db-&gt;cache_delete()<a class="headerlink" href="#this-db-cache-delete" title="Permalink to this headline">¶</a></h2>
    553. 

  553. <p>Deletes the cache files associated with a particular page. This is
    554. 

  554. useful if you need to clear caching after you update your database.</p>
    555. 

  555. <p>The caching system saves your cache files to folders that correspond to
    556. 

  556. the URI of the page you are viewing. For example, if you are viewing a
    557. 

  557. page at example.com/index.php/blog/comments, the caching system will put
    558. 

  558. all cache files associated with it in a folder called blog+comments. To
    559. 

  559. delete those particular cache files you will use:</p>
    560. 

  560. <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_delete</span><span class="p">(</span><span class="s1">&#39;blog&#39;</span><span class="p">,</span> <span class="s1">&#39;comments&#39;</span><span class="p">);</span>
    561. 

  561. </pre></div>
    562. 

  562. </div>
    563. 

  563. <p>If you do not use any parameters the current URI will be used when
    564. 

  564. determining what should be cleared.</p>
    565. 

  565. </div>
    566. 

  566. <div class="section" id="this-db-cache-delete-all">
    567. 

  567. <h2>$this-&gt;db-&gt;cache_delete_all()<a class="headerlink" href="#this-db-cache-delete-all" title="Permalink to this headline">¶</a></h2>
    568. 

  568. <p>Clears all existing cache files. Example:</p>
    569. 

  569. <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_delete_all</span><span class="p">();</span>
    570. 

  570. </pre></div>
    571. 

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