What is Object Caching?

[raamdev]

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title: What is Object Caching?
categories: questions
tags: 
author: raamdev
github-issue: 

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[Referencing internal discussion with Jason where he describes the pros and cons of object caching, and explains what it is: https://websharks.slack.com/archives/comet-cache/p1462486001000589]

WordPress comes with its own Object Cache built-in (see WP Object Cache), as do many plugins for WordPress (including bbPress). The drop-in plugin file /wp-content/object-cache.php allows for a so-called Advanced Object Cache to take things a step further; e.g., caching transients into memory, and doing a persistent cache of what WordPress already deals with. We have not seen a single reliable implementation of an Advanced Objet Cache. Object caching that comes with WordPress already + Page caching with a plugin like Comet Cache is generally more than enough and the only scenario where it makes sense to add another layer of Advanced Object Caching is on completely custom, very high traffic WordPress sites where every single plugin and even the theme itself has been reviewed and tweaked to take advantage of the Advanced Object Cache (e.g., the NY Times blogs, which have a team of WordPress developers who tweak WordPress for high-availability).

Object caching is very specific to the PHP code itself (i.e., where the objects are created; the PHP code needs to take into consideration that the objects it creates might get cached). Many WordPress plugins are not written with object caching in mind, which is why adding Advanced Object Caching to a WordPress site with many different WordPress plugins often causes strange and seemingly mysterious issues. Larger and more well-maintained plugins like bbPress and BuddyPress are already written to take advantage of object caching, so adding another Advanced Object Cache will generally not produce any improvement in speed when it comes to those plugins.