Cache/zh-tw

Joomla 使用不同的方式來快取"內容"。以下是關於管理員以及開發者何時、如何、何處以及有哪些快取的總覽。

系統管理員

作為系統管理員，Joomla 提供了快取功能，您可以選擇全站快取，或是僅快取部分頁面。以下介紹如何進行。

在 Joomla 網站中有三種內容可以被快取：

1. 整個頁面本身 – 頁面快取
2. 來自joomla 元件，顯示於該頁面上的輸出 – 我們稱為視覺快取 (View cache)
3. 來自joomla 模組，顯示於該頁面上的輸出 – 我們稱為模組快取 (Module cache)

您有好幾個快取設定可以讓您控制要建立哪些快取：

1. 系統外掛 "System – Page Cache"
2. 全站設定，系統頁籤，快取設定。在此您可以設定系統快取選項
   • OFF – 停用快取
   • ON – 啟用保守快取
   • ON – 啟用累進快取
3. 在許多模組的設定頁面中，有進階設定頁籤可以設定是否要使用全站設定，或是停用快取

As described below, there are also rules for caching which are implemented within the Joomla code, and over which you have no control.

您可以從管理員選單項目「系統」➞「清除快取」來清除快取。

一般而言，您可以想像成Joomla 有三個層級的快取原則，愈底下愈積極

1. 保守快取
2. 累進快取
3. 頁面快取

接著我們會詳細地來看看這三個項目

此外，joomla開發者可以使用快取機制來儲存...舉例來說，資料庫的檢索結果，以提升網站的反應速度，然而這已經超出系統管理員的範圍了。

頁面快取

To switch this on, go to Administrator → Extensions → Plugins. Then find the System – Page Cache plugin, and enable it. This means that site pages will now be cached and whenever they're requested again, the cached page will be served, rather than it being generated by Joomla from the information in the database. The cached page will continue to be served until it's expired – as defined by the Cache Time parameter in the Administrator → Global Configuration → System tab → Cache Settings.

If you're reading this page as a tutorial and want to test the page caching, it's best to set the Global Configuration cache settings to:

• Cache Handler – File
• Path to Cache Folder – leave blank
• Cache Time – 15 (the default of 15 minutes)
• Platform Specific Caching - No
• System Cache – OFF – Caching disabled

To verify that page caching is working, go to a website page that displays an article. After you display that page you should find in the file system a cache/page directory with a file in it which has a filename like <string of hex digits>-cache-page-<string of hex digits>.php. (Joomla has to store separate cache pages for separate URLs so the second string of hex digits is a hash of the URL of the site web page, to make the filename unique to that page).

Then use the Administrator functionality to change the text of that article, and redisplay the site web page. You should find the cached version, not your modified text.

Changing an article (or other Joomla item) does not clear the page cache for the web page(s) where that article is displayed. To clear the page cache go to Administrator → System → Clear Cache. Click on the checkbox next to the Cache Group called "page", and press the Delete button. When you redisplay your web page it should now show your amended text.

If your site has a function like a shopping basket, applying page caching will cause problems, as pages have to show what the customer has already selected, rather than displaying a cached page which is common to everyone. However, you can configure the System - Page Cache plugin to exclude caching specified Menu Items or specified URLs and URL ranges (in the Advanced tab), so that only truly static pages are cached.

保守快取

With Conservative Caching you can cache the View output from components and the output from those Modules which allow caching. But note that this will work only on pages which are not cached using the Page Cache. For those pages the whole web page is cached, and Conservative Caching isn't even considered.

To switch on Conservative Caching:

1. Go to Administrator → System → Global Configuration → System tab and within Cache Settings, set System Cache to ON – Conservative caching
2. Go to Administrator → Extensions → Modules and select the modules which you'd like to be cached. If that module permits caching then under the Advanced tab you should be able to set Caching to

• Use Global – this module will be cached (with the Global option now having been set to Conservative caching)
• No caching – this module will not be cached.

(Note that the Cache Time in the Global Configuration is in minutes but the Cache Time in the Module settings is in seconds.)

To check it's working, go to your site, ensure that you are logged out, and navigate to a web page which displays an article. Check your file system and you should find a folder cache/com_content containing a cache file.

You'll also find other directories such as cache/com_languages (as displaying the page involves loading the current language, and this will be cached as well) and also directories relating to module cache, e.g. cache/com_modules. These result from the use of cache which developers have coded within the Joomla application.

If you edit and save that article then refresh the site page, you will find that the site displays the updated text this time. This is because whenever the edit is saved, Joomla clears the cache for that article.

However, you can demonstrate that the cache is working if you edit the cache file in the cache/com_content directory using a basic text editor. Using the editor, change one letter within the article text in the cache file and save the file. Then when you refresh the web page you should see the change that you made to the cache file.

How can you select which component views get cached, and under what circumstances? Alas, you can't do this. This is determined by the Joomla core component developers and coded in the component PHP code. The criteria are different for each component. However, you can easily discover what criteria are used because for each of the site components they are coded in the site controller.php file. For example, at the time of this writing (Joomla version 3.9.2) for the Contacts component we find in components/com_contact/controller.php

if (JFactory::getApplication()->getUserState('com_contact.contact.data') === null)
{
	$cachable = true;
}

This means that the views associated with contacts will be cachable unless there is session data keyed by com_contact.contact.data – which will be the case if in the user session the user has displayed a contact form (e.g. on a page pointed to by a menu item of type Contacts → Single Contact).

The equivalent file for articles components/com_content/controller.php contains:

$cachable = true;
if ($user->get('id') || ($this->input->getMethod() === 'POST' && (($vName === 'category' && $this->input->get('layout') !== 'blog') || $vName === 'archive' )))
{
	$cachable = false;
}

The expression $user->get('id') is true if this is a logged-in user. This means that articles are never cached for logged-in users. The subsequent expressions relate to other conditions when the caching is not performed, even if the user is not logged in.

So in this way you can discover the circumstances under which caching is performed, but changing these is not advisable.

You can also demonstrate that modules are being cached by using the Joomla Breadcrumbs module, ensuring it's displayed in some module position on the web page, setting its Caching option and manually editing the cached file in cache/mod_breadcrumbs.

Progressive Caching

Like Conservative Caching, Progressive Caching also caches the output from component views and from modules. The functional difference between the two is that with Progressive Caching for logged-off users all modules are always cached. In this case, setting the No Caching option for a module has no effect. If the caching storage option is to File, you can find the modules cache file (the output from all modules is stored within the same file) within the cache/com_modules directory.

To switch on Progressive Caching, go to Administrator → System → Global Configuration → System tab and within Cache Settings set System Cache to ON – Progressive caching.

As regards the conditions for caching of Joomla core component views, there is no difference between conservative and progressive caching. Despite what you may read on some websites and responses to Stack Overflow questions, it is not the case that Conservative Caching relates to when the user is not logged on and Progressive Caching to when the user is logged on.

摘要

以下是各種類型的快取。

頁面快取

• Configuration: Built-in Plugin (Administrator → Extensions → Plugin Manager → System - Page Cache)
• Caches: each whole page of your site
• Based on: URL

• More info:
  • Optional browser caching: Also caches on your visitors' browser/computer
  • Only caches pages for guest visitors (not for logged in visitors). Be careful using this plugin if you have an interactive site where you want to server content based on session/cookie information rather than on the plain URL only. Features like a shopping cart will not work.

View Caching

• Configuration: Global Config -> Cache
• Caches: each view of a component
• Based on: URL, view, parameters, ...
• More info: Component developers have to include this in their code to work. Mostly this is not done. The Joomla main content component uses this, but only for guest visitors of your site though this is not obligated for every component.

模組快取

• Configuration: Global Config -> Cache
• Caches: each module (individually customized via each module's Advanced Parameters)
• Based on: the module id, the user's view levels and the Itemid parameter in the HTTP request
• More info: You must disable it on some modules to avoid problems

進階快取

假如您還想要看看關於快取還有什麼其他的可能性，您可以查看第三方擴充套件中關於快取的項目。

Caching engines or storages

• Configuration: Global Config -> Cache

Here you can choose which system you want your site to use for all caching. Some options are: APC, Eaccelorator, File, Memcache, Redis, XCache.

例如，APC也會快取您的php opcode

開發者

class JCache 允許多種不同種類以及層級的快取。其下的 sub-classes 用於特定的內容，然而您可以添加您自己的，或是在不同的應用方式中，使用主要項目。

Don't forget that the first level of cache encountered, will override any deeper caching. I suppose that too many levels is also counterproductive (to be verified though).

• JCacheView caches and returns the output of a given view (in MVC). A cache id is automatically generated from the URI, specific view and its specific method, or you can give your own.

This can automatically be done via the base controller's display function. For example in the controller of your component:

class DeliciousController extends JController {
	function display() {
		parent::display(true); //true asks for caching.
	}
}

There are also some urlparams to consider. Check this "joomla stack"

Also, be aware that any updates (such as hits or visit counts) will NOT be updated (unless you add this outside this method and thus any deeper MVC-part.)

• JCachePage caches and returns the body of the page.
• JCacheCallback caches and returns the output and results of functions or methods.

If you want to cache queries, this is a good class for it, as illustrated here: Using caching to speed up your code

• JCacheOutput caches and returns output.

This is rather meant for caching a specific part of PHP code. It acts like an output buffer, but cached.

參考

• Better performance with Joomla System Cache plugin (Joomla Forum)
• JCache
• How can I use Joomla's Cache with my components view? (joomla stackexchange beta)