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WordPress has a lot of dynamic functionality, but this comes at a cost. Tasks such as processing PHPPHPPHP (PHP: Hypertext Preprocessor) is a general-purpose scripting language especially suited to web development. PHP code is usually processed on a web server by a PHP interpreter. On a web server, the result of the interpreted and executed PHP code would form the whole or part of an HTTP response., querying the databaseDatabaseA database is an organized collection of data. Access to this data is usually provided by a "database management system" (DBMS) consisting of an integrated set of computer software that allows users to interact with one or more databases and provides access to all of the data contained in the database. Because of the close relationship between them, the term "database" is often used casually to refer to both a database and the DBMS used to manipulate it. and collecting information from external APIs all take resources and time.
CachingCacheA cache is a component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere. saves time for potentially heavy tasks by reusing previously computed results, rather than calculating them for every page view.
CachesCacheA cache is a component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere. typically expire after a certain amount of time and are regenerated so the most recent content is displayed. When items are served from cacheCacheA cache is a component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere. they have a faster response time, often coming from memory, and take load off the serverServerA server is a piece of computer hardware or software that provides functionality for other programs or devices. Typical servers are database servers, file servers, mail servers, print servers, web servers, game servers, and application servers..
In a typical page load, various caches might be checked in the following order:
Local Browser cache / Local Storage / Web App Manifest
Full Page Cache (Reverse Proxy – Varnish or NGINXNGINXnginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache. Nginx is free and open-source software, released under the terms of the 2-clause BSD license.)
Static Cache (JS, CSSCSSCSS is an acronym for cascading style sheets. This is what controls the design or look and feel of a site., Images with static caching services, NGINX tryfiles, etc.)
Object Cache (wp_options, transientTransientWordPress Transients offers a simple and standardized way of storing cached data in the database temporarily by giving it a custom name and a timeframe after which it will expire and be deleted.APIAPIAn Application Programming Interface (API) is a computing interface that defines interactions between multiple software intermediaries. It defines the kinds of calls or requests that can be made, how to make them, the data formats that should be used, the conventions to follow, etc.)
Each caching instance may be a different domainDomainA domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet. Something like example.com., server, or compute instanceCompute instanceIn Cloud Computing, an instance is a virtual server., either routed by the local machine, the remote server cluster, or any intermediary computer along the request chain. It is recommended to check with your hostingHostingA web hosting service is a type of Internet hosting service that allows individuals and organizations to make their website accessible via the World Wide Web. company for server-side solutions like Varnish and NGINX which usually works faster than plugins and file based full page caching.
Each cache may have any configuration of:
Data storage: RAMRAMRandom-access memory (RAM) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code., SSD, or spinning hard drives. Physical connection, or data over network.
Input/Output latency: Connection from local or remote server motherboard to RAM, Data I/O, or network I/O.
For any given page load, speed and user experience will result from the combined latency of all services, and the order they are processed as users interact with a web application.
(Example: CSS; Generated by JavaScriptJavaScriptJavaScript, often abbreviated as JS, is a programming language. It has curly-bracket syntax, dynamic typing, prototype-based object-orientation, and first-class functions. Alongside HTML and CSS, JavaScript is one of the core technologies of the World Wide Web., PHP or pre-processor. Sent over network. Earliest display: Inline script within first HTTPHTTPThe Hypertext Transfer Protocol (HTTP) is protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, where hypertext documents include hyperlinks to other resources that the user can easily access, for example by a mouse click or by tapping the screen in a web browser. packet of first HTMLHTMLHypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. HTML describes the structure of a web page semantically and originally included cues for the appearance of the document. response. Typical: Loaded by many plugins in many files over many requests. Middle-ground: combined file, cached locally, to CDNCDNA Content Delivery Network (CDN) is a geographically distributed network of proxy servers and their data centers. The goal is to provide high availability and performance by distributing the service spatially relative to end users. CDNs have grown to serve a large portion of the Internet content today, including web objects (text, graphics and scripts), downloadable objects (media files, software, documents), applications (e-commerce, portals), live streaming media, on-demand streaming media, and social media sites., or server RAM or SSD.)
Content Delivery Networks are designed to optimize the network latency between servers and visitors from different geographical locations. Data is distributed amongst endpoints and then visitors get served from the endpoint which is closest to them.
In addition to optimizing networking latency, CDNs can act as another layer of static and/or full-page caching running on all those endpoints.
It’s important to make sure that CDNs are working well with all your other caching systems and that it purges caches on all endpoints when you request that from your main server. Otherwise, people in certain areas may get old results which is generally an issue that’s difficult to troubleshoot.
Note, that if you don’t have full page caching on the CDN edges, this might increase the TTFB (time to first byte) because the node must fetch the data from the origin server before serving it to the end user.
In order to display your content, WordPress does a lot of work under the hood, and all those calculations require server resources and time to complete. For starters, the PHP service on the server has to process the request, load WordPress coreCoreCore is the set of software required to run WordPress. The Core Team builds WordPress., your themeThemeA theme dictates the style and function of your WordPress website. Child Themes derive from the main parent theme. PHP files and all PHP scripts coming from your plugins. The majority of those PHP files make requests to your database, too, which adds to the overall resource footprint of your site.
The best way to cache these requests is to use a reverse proxy like NGINX or Varnish which stores the output directly into the server memory or hard disk. That saves a lot of processing power because cached content is served straight out of the reverse proxy without hitting your web serverServerA server is a piece of computer hardware or software that provides functionality for other programs or devices. Typical servers are database servers, file servers, mail servers, print servers, web servers, game servers, and application servers., the PHP service, or your database service at all. If a reverse proxy is not available on your current server setup, you can fallback to storing cached content into your file system. It’s slower than reverse proxies and a hit reaches your web server and your PHP service at least once, so it can direct the request to the proper cached file but still – it’s much faster than doing all the computing for every request.
Full Page Caching stores the HTML output of a request, but all the CSS, JS, images and font files will have to be loaded separately too. They are handled separately and optimizing them is worth investing the time and effort. Static caching can have great effect on those resources. You can often use the same reverse proxy to static resources in the server memory – CSS, JS, Fonts, Images and serve them directly.
It’s important to have the ability to expire caches when necessary to avoid serving visitors old data. When available, selective caching is preferred over purging the entire cache, to avoid the cost of WordPress regenerating every page for the site. Furthermore, it’s good practice to exclude certain types of pages from your full page caching completely because they are different for each user. For example, if you have an online store, it’s imperative that your cart, checkout and profile pages are completely dynamic. In general, it’s a good idea to exclude all logged in users from the cache because they are supposed to see personalized content. Another important aspect is the default caching period, which can be different for each website depending on how often data is changed.
In 2005, WordPress introduced its internal objectObjectIn computer science, an object can be a variable, a data structure, a function, or a method, and as such, is a value in memory referenced by an identifier. cache — a way of automatically storing any data from the database (not just objects) in PHP memory to prevent unnecessary queries. However, out of the box, WordPress will discard all of those objects at the end of the request, requiring them to be rebuilt from scratch for the next page load. In addition to that, you can use persistent object caching mechanisms like RedisRedisRedis (Remote Dictionary Server) is an in-memory data structure store, in-memory key–value database. It is open-source software.. or MemcachedMemcachedMemcached is a general-purpose distributed memory-caching system. It is often used to speed up dynamic database-driven websites by caching data and objects in RAM to reduce the number of times an external data source must be read. Memcached is free and open-source software. which, however, require additional plugins (drop-ins) which allow WordPress to use these services.
What does this mean? Think of a standard WordPress homepage displaying the most recent posts. Each of these posts has quite a bit of information associated with it WordPress must look up such as the author, categories, tags, and excerptExcerptAn excerpt is the description of the blog post or page that will by default show on the blog archive page, in search results (SERPs), and on social media. With an SEO plugin, the excerpt may also be in that plugin’s metabox..
Support for a persistent object cache gives WordPress, plugins, and themes, a place to store that data for reuse. While these items are cached, PHP execution time is improved while lessening the load on the database. It’s particularly helpful in situations where much of the page is difficult to cache from the front-end, like for authenticated traffic or e-commerce applications.
For these reasons, persistent object caching support is commonly offered with managed WordPress hosting.
TransientsTransientWordPress Transients offers a simple and standardized way of storing cached data in the database temporarily by giving it a custom name and a timeframe after which it will expire and be deleted. are inherently sped up by caching plugins, where normal Options are not. A memcached pluginPluginA plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the WordPress.org Plugin Directory or can be cost-based plugin from a third-party., for example, would make WordPress store transient values in fast memory instead of in the database. For this reason, transients should be used to store any data that is expected to expire, or which can expire at any time. Transients should also never be assumed to be in the database, since they may not be stored there at all.
The web server must read, compile, and run each PHP script. An opcode cache stores a compiled copy of each PHP script in memory or on disk. When the web server starts processing PHP scripts for WordPress, the web server checks the opcode cache for a cached copy of the PHP script. If there is a cached copy, the web server can skip straight to running the PHP script using the cached copy instead of having to read and compile the script again. Skipping this reading and compiling PHP scripts can greatly improve the web server’s resource usage and enable WordPress to serve many more requests than it might have been able to otherwise. It’s particularly helpful for dynamic content and authenticated traffic, where full page caching isn’t as effective.
As with any cache, opcode caches can keep changes from taking effect until the cache expires or is purged. With opcode cache specifically, this means older versions of the compiled PHP code will be loaded. When updating plugins, themes, or WordPress core, the appropriate files should be purged from the cache to avoid continuing to load the older versions.
This caching method allows saving sections of otherwise non-cacheable dynamic website content. It can help especially for sites where the majority of the page is static, but has certain dynamic elements, like a shopping cart, or for membership sites.
In the WordPress context, developers often store parts of the page using the WordPress transients/object cache API. In these cases, providing a persistent object cache will allow that caching to happen outside of the database.
Storing these fragments separately in a front end cache is not natively supported by WordPress, and means both manually configuring the sections of the page to be cached, and configuring your front-end cache, whether it be Nginx, Varnish, or otherwise, to support fragment caching. This is usually an advanced technique, and reserved for sites or hosting platforms with very high dynamic traffic needs.
Purging caches is as important as storing them. You have to make sure that all layers of caching are cleared when necessary.
Fragment caching is the temporary storage of expensive or long-running server-side operations to avoid taxing web servers and delayed delivery to visitors. It’s become a common practice for operations such as generating Menu markup, WidgetWidgetA WordPress Widget is a small block that performs a specific function. You can add these widgets in sidebars also known as widget-ready areas on your web page. WordPress widgets were originally created to provide a simple and easy-to-use way of giving design and structure control of the WordPress theme to the user. markup and slow MySQLMySQLMySQL is an open-source relational database management system (RDBMS). MySQL is free and open-source software under the terms of the GNU General Public License. or HTTP responses. Core currently uses transients to cache HTTP calls to WordPress.orgWordPress.orgThe community site where WordPress code is created and shared by the users. This is where you can download the source code for WordPress core, plugins and themes as well as the central location for community conversations and organization. https://wordpress.org/ APIs for updates and events.
Fragment caching is particularly beneficial when appropriately paired with full-page caching. Perhaps there’s uniform <footer> markup displayed on every page that can be temporarily stored. When the server needs to rebuild static cache files and a fragment is found, it saves the server from running Menu/Widget queries to generate the footer markup on every page.
Significant caution should be exercised blanket caching Core resources. If a site Menu relies on dynamic .current-menu-item classes, storing the menu markup in a fragment will “burn” that class in, no longer highlighting the correct page as a user navigates. Any caching of WordPress Core resources should be opt-in and integrate an appropriate flushing mechanism for when users modify the resource.
The Transients API should always be used for fragment caching instead of directly using wp_cache_* functions. In environments without a persistent Object Cache, set_transient() will store cache values in the database in the wp_options table. However, when Object Cache is enabled, set_transient() will wrap wp_cache_set().
2023-09-14: Moved PHP Optimization to Advanced Administration.
2021-05-27: Fixing infoboxes
2021-02-17: Changelog added
2020-11-09: Lifted PHP Recommendation to 7.4
2020-06-02: Published from GithubGitHubGitHub is a website that offers online implementation of git repositories that can can easily be shared, copied and modified by other developers. Public repositories are free to host, private repositories require a paid subscription. GitHub introduced the concept of the ‘pull request’ where code changes done in branches by contributors can be reviewed and discussed before being merged be the repository owner.
