SharePoint Server 2016 provides three types of caches that help improve the speed at which web pages load in the browser: the BLOB cache, the ASP.NET output cache, and the object cache.
The BLOB cache is a disk-based cache that stores binary large object files that are used by web pages to help the pages load quickly in the browser.
The ASP.NET output cache stores the rendered output of a page. It also stores different versions of the cached page, based on the permissions of the users who are requesting the page.
The object cache reduces the traffic between the web server and the SQL database by storing objects such as lists and libraries, site settings, and page layouts in memory on the front-end web server. As a result, the pages that require these items can be rendered quickly, increasing the speed with which pages are delivered to the client browser.
The monitors measure cache hits, cache misses, cache compactions, and cache flushes. The following list describes each of these performance monitors.
A cache hit occurs when the cache receives a request for an object whose data is already stored in the cache. A high number of cache hits indicates good performance and a good end-user experience.
A cache miss occurs when the cache receives a request for an object whose data is not already stored in the cache. A high number of cache misses might indicate poor performance and a slower end-user experience.
Cache compaction (also known as trimming), happens when a cache becomes full and additional requests for non-cached content are received. During compaction, the system identifies a subset of the contents in the cache to remove, and removes them. Typically these contents are not requested as frequently.
Compaction can consume a significant portion of the server’s resources. This can affect both server performance and the end-user experience. Therefore, compaction should be avoided. You can decrease the occurrence of compaction by increasing the size of the cache. Compaction usually happens if the cache size is decreased. Compaction of the object cache does not consume as many resources as the compaction of the BLOB cache.
A cache flush is when the cache is completely emptied. After the cache is flushed, the cache hit to cache miss ratio will be almost zero. Then, as users request content and the cache is filled up, that ratio increases and eventually reaches an optimal level. A consistently high number for this counter might indicate a problem with the farm, such as constantly changing library metadata schemas.
You can monitor the effectiveness of the cache settings to make sure that the end-users are getting the best experience possible. Optimum performance occurs when the ratio of cache hits to cache misses is high and when compactions and flushes only rarely occur. If the monitors do not indicate these conditions, you can improve performance by changing the cache settings.
The following sections provide specific information for monitoring each kind of cache.
Monitoring BLOB cache performance:
For the BLOB cache, a request is only counted as a cache miss if the user requests a file whose extension is configured to be cached. For example, if the cache is enabled to cache .jpg files only, and the cache gets a request for a .gif file, that request is not counted as a cache miss.
Monitoring ASP.NET output cache performance :
For the ASP.NET output cache, all pages are cached for a fixed duration that is independent of user actions. Therefore, there are flush-related monitoring events.
Monitoring object cache performance :
The object cache is used to store metadata about sites, libraries, lists, list items, and documents that are used by features such as site navigation and the Content Query Web Part.
This cache helps users when they browse to pages that use these features because the data that they require is stored or retrieved directly from the object cache instead of from the content database.
The object cache is stored in the RAM of each web server in the farm. Each web server maintains its own object cache.
You can monitor the effectiveness of the cache settings by using the performance monitors that are listed in the following table.