Object Caching
How Object Caching Stores Reusable Data
Object caching is the practice of storing small pieces of data, such as database query results or computed values, in fast memory so the application can reuse them instead of recalculating them. It is one form of server-side caching. Each stored item is called an object, and the cache is usually a separate service that runs alongside the web application.
Dynamic sites ask the same questions many times. A page may request the site title, the menu items or a plugin's settings on every load. Without object caching, each request sends these questions to the database and waits for the answers. With object caching, the first answer is saved in memory, and later requests read it directly. Memory access is much faster than a database query, so pages are built sooner and the database handles less work.
Why It Matters for Logged-In and Dynamic Pages
Page caching works best when every visitor sees the same page. Logged-in users, shoppers and members usually see personalized content, which a page cache cannot share safely. Object caching fills that gap. The page is still built for each visitor, but the data many pages share comes from memory.
The benefit depends on the site. A site with few queries per page gains little. Sites that run many queries, such as large catalogs or complex plugin setups, often see larger drops in database load. Object caching also does not remove the need for sound database design.
Cached objects need an expiry rule and a way to refresh when the underlying data changes. Applications usually handle this automatically, but poorly designed cache keys can return outdated data. Two common in-memory stores for this job are compared in Redis and Memcached.
Example: An Online Shop With Signed-In Customers
Consider an online shop where most visitors browse anonymously and some customers sign in to check their orders. Product pages for anonymous visitors can come from a page cache. A signed-in customer's account page cannot be shared, so the server builds it for each request. Object caching then stores the category tree, shop settings and product details that all of these pages use. The customer still gets a personal page, but the server does not query the same data over and over.
Frequently asked questions
What Is the Difference Between Object Caching and Page Caching?
Page caching saves the finished HTML of an entire page and serves it as is, so no page building happens at all. Object caching saves smaller pieces, such as query results, and the page is still assembled for each request. Page caching is faster when it can be used. Object caching is more flexible because it helps pages that cannot be shared. Many sites use both.
Does Object Caching Need a Separate Server?
Not always. Some setups keep objects in memory on the same machine as the application. Others use a separate cache service that several web servers can share. A separate service adds a network step and one more component to monitor, but it lets multiple servers use the same cached data. The right choice depends on the size of the site and how the hosting environment is built.