CodeIgniter Profiler Output and Cache Handler Selection: Choosing the Right Backend

After enabling the CodeIgniter Profiler to identify slow database queries, the next step is to select a cache backend that will reduce the observed load.

The Profiler is available only in development environments and its output varies between CodeIgniter 3 and 4, while the choice of cache handler (file, Memcached, Redis, or APCu) depends on factors such as server count, memory availability, and persistence requirements.

Which cache handler delivers the greatest reduction in query execution time for the identified bottleneck? How does the selected handler affect the Profiler‑reported query count and total execution time when re‑run in a staging environment? What version‑specific configuration differences must be considered when applying the chosen handler in CodeIgniter 3 versus CodeIgniter 4?