A cache server is a dedicated network server or service acting as a server that saves Web pages or other Internet content locally. By placing previously requested information in temporary storage, or cache, a cache server both speeds up access to data and reduces demand on an enterprise’s bandwidth.
Cache servers also allow users to access content offline, including rich media files or other documents. A cache server is sometimes called a “cache engine.”
It is very important that how much time your page took to upload. If it is taking too much time, It’s not a good sign for you. Because it is affecting your user experience as well as SEO of your website.
So it is necessary that your page must be served within a second.
Varnish is a most popular HTTP web caching server which is really much, much faster. You can install varnish in front of any server.
Varnish is present in front of your main server. So every request firstly processed by varnish instead of your web server. And if it found corresponding content on varnish cache it will not let the request to bother your main web server and serve the content itself.
If your content is not available at Varnish your request will be sent to Main server and varnish will save the response of that request in its cache so that next time varnish can return the response instead of the web server.
So load on your backend server will be reduced significantly. Varnish can increase your site speed thousand times.
There are a lot of configuration options available in varnish. Like You can set a time limit of your varnish server, you can save different response for mobile and desktop for the same URL and much more.
Varnish is heavily threaded, with each client connection being handled by a separate worker thread. When the configured limit on the number of active worker threads is reached, incoming connections are placed in an overflow queue; when this queue reaches its configured limit incoming connections will be rejected.
Memcached is a general-purpose distributed memory caching system which stores information in the key-value pair.
It is used to speed up dynamic database-driven websites. Memcache helps reduce database load by caching DB objects in RAM. Memcache helps reduce database load by caching DB objects in RAM.
You can use it to store things like strings, numeric values, objects, and arrays.
The application then uses its Memcached client to talk to the Memcached server and ask for cached content.
Memcached is faster than querying data from a traditional database because Memcache server just searches value mapped to the key instead of scanning entire table or database.
It works on the concept of LRU(least recently used). So when the caching disks are full, it purges(remove) the content which has not been used for ages.
Memcache is a back-end caching server while varnish is a front-end caching server.
“Memcached is sometimes more efficient, but Redis is almost always the better choice.”
Redis is also an in-memory caching server works pretty much similar to the Memcached. It supports data structures such as strings, hashes, lists, sets, sorted sets with range queries, bitmaps and geospatial indexes with radius queries.
It’s high-speed fully in-memory database. It does persist data on disk.
Redis gives you much greater flexibility regarding the objects you can cache. While Memcached limits key names to 250 bytes and works with plain strings only, Redis allows key names and values to be as large as 512MB each.
Redis helps us to build software that handles thousands of requests per second and keep customer business data during the whole natural lifecycle.