What an object cache is, and why WordPress needs a plugin for it
WordPress already has an object cache, but the developer reference for WP_Object_Cache states that by default the object cache is non-persistent: data resides in memory only and only for the duration of the request. Cached data will not be stored persistently across page loads unless you install a persistent caching plugin.
A persistent backend keeps those results in a separate memory store so the next request can reuse them. The Redis Object Cache plugin on WordPress.org describes itself as a persistent object cache backend powered by Redis and lists support for Predis, PhpRedis, Relay, replication, sentinels, clustering and WP-CLI. Its listing shows WordPress 4.6 or higher and PHP 7.2 or higher. You still need a Redis server, which is what the host add-ons provide.
Why this matters more for members than for blogs
Page caches skip logged-in users. In the file-based caching section of its Speed Optimizer tutorial, SiteGround states that by default it does not cache content for logged in users, and Cloudflare documents a logged-in bypass for APO. So every lesson view, quiz submission and account page for a logged-in student runs PHP and queries the database.
Those requests repeat a lot of the same lookups: site options, user meta, membership rules, course structure. An object cache can serve those from memory. Kinsta's Redis documentation says the add-on is especially beneficial for resource-intensive applications, naming WooCommerce stores, membership sites and high-traffic installations, and recommends Redis for highly dynamic websites that cannot make good use of page caching. The same page says Redis will generally not help the load time of static blogs.
What it will not fix: a slow report query that runs once with unique parameters, a plugin that calls a remote API on every page, or a PHP worker shortage during a launch. Diagnose first; our guide on slow logged-in MemberPress users covers that sequence.
How three managed hosts offer it
Cost math for Kinsta: $100 per month is $1,200 per year for one site, before the hosting plan itself. For a membership site where logged-in performance is the main complaint, compare that against moving up a plan tier or fixing the slowest plugin, using measurements from your own site.
| Host | What is offered | Published price or default | Documented limits and notes |
|---|---|---|---|
| Kinsta | Redis add-on: a dedicated 2GB Redis instance in the same container as the site; installs the Redis Object Cache plugin by default | $100 per month per site | Only company owners, company admins and company billing users can enable it; prorated fee or credit if removed |
| WP Engine | Object caching toggled per environment in the User Portal under Caching | Default state on new environments is enabled; plan inclusion not stated on the support page | Object cache size buffer is 1Mb; keep autoloaded data below 800,000 bytes; large autoloaded data can cause 502 errors |
| SiteGround | Memcached through SuperCacher in Site Tools, configured for WordPress through the Speed Optimizer plugin | Plan tiers not stated in the tutorials read | Memcached and Dynamic Caching are available only for sites hosted at SiteGround |
Pitfalls when you turn it on or move hosts
- Autoloaded options: WP Engine documents that large autoloaded data can cause 502 errors and that temporarily disabling object caching can clear them while you reduce the data. Check the size of autoloaded options before enabling a cache anywhere.
- Clearing: WP Engine notes its object cache is not cleared on a timed schedule; least recently used entries are removed when space is needed. Purge it after bulk imports or URL changes so members do not see stale settings.
- Drop-in files: a persistent cache is wired in through a drop-in or mu-plugin, and WP Engine notes it may use either depending on server type. When migrating, confirm the destination provides the same backend before copying an object-cache drop-in across.
- Billing permissions: on Kinsta, a developer user without billing permission cannot enable the add-on; plan who will approve it.
- Cancelling: Kinsta documents a prorated fee if the add-on is removed within the first 30 days of the plan, and a prorated credit after that.
A decision procedure before you pay
Measure a logged-in lesson page and a member account page with a query monitor tool, logged in as a real test student. If a large share of time is repeated option and meta lookups, an object cache is a strong candidate. If time is dominated by one slow query or an external call, fix that first; a cache will not help it.
Who should buy: membership and course sites with many concurrent logged-in members and repeated lookups. Who should skip: sites whose traffic is mostly anonymous and already page-cached, and static blogs, which Kinsta itself says Redis will generally not help.
Questions before you decide
Is Redis the same as page caching?
No. A page cache stores whole HTML pages and is normally skipped for logged-in users. An object cache stores database results reused while building a page, so it still runs for logged-in members.
Can I install the Redis Object Cache plugin on any host?
The plugin needs a reachable Redis server. Without one provided by the host or your own server, the plugin has nothing to connect to.
Sources & verification
Product details and prices can change. Check the linked provider before buying.
- WordPress Developer Resources: WP_Object_Cache Accessed 13 Oct 2026
- WordPress.org: Redis Object Cache plugin Accessed 13 Oct 2026
- Kinsta: Redis caching Accessed 13 Oct 2026
- WP Engine: Manage object cache Accessed 13 Oct 2026
- SiteGround: Memcached tutorial Accessed 13 Oct 2026
- SiteGround: Speed Optimizer caching Accessed 13 Oct 2026
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