Redis Caching Setup for OpenCart

Redis caching setup for OpenCart

The file-based cache that ships by default performs acceptably on a small store. As the catalogue and traffic grow it becomes a bottleneck in its own right: every cache lookup is a disk operation, and there are dozens per page.

What is included

• installing and configuring Redis with a memory limit and an eviction policy;
• connecting the store to Redis instead of the file cache;
• a separate key namespace where several sites share a server — otherwise they overwrite each other's cache;
• cache lifetime tuned to how often your catalogue changes;
• session storage in Redis, where appropriate;
• checking the cache hit rate: if it is low, the setup achieves nothing.

What nobody warns you about

OpenCart's built-in cache invalidation is written for file storage: it deletes a group of keys by pattern. On Redis that does not work — only an exact key is removed. The consequence: you change a product and the site keeps showing the old price until the cache lifetime expires.

So connecting Redis is not just "switch the driver in the config" — it also means verifying that cache clearing after an edit genuinely works.

When Redis is not needed

If the store has a few hundred products and a dozen visitors an hour, you will not notice a difference. Redis pays off where there is load: a large catalogue, active traffic, heavy category pages.