A slow OpenCart is one of the most common problems store owners run into. This walkthrough covers the process from analysis to result.
Step 1: read the slow query log
Start by enabling the slow query log in MySQL/MariaDB:
slow_query_log = 1 slow_query_log_file = /var/log/mysql/slow.log long_query_time = 0.5
Use pt-query-digest to find the heaviest queries. The usual culprits are oc_product, oc_product_description and oc_category_path.
Step 2: indexes and queries
Add composite indexes on the fields you filter by most. A classic case: category page queries doing a full table scan because there is no index on (status, date_available).
Step 3: FastCGI cache
Nginx FastCGI cache gives the biggest single win on static pages. TTFB drops from 2–4 seconds to 10–50 ms on cached pages. Configure exclusions for the cart and the admin panel.
Step 4: Redis object cache
OpenCart supports Redis through its standard cache driver. Moving session and object cache off disk and into Redis speeds up dynamic pages by 30–50%.
Step 5: OPcache and JIT
PHP 8.x JIT compilation adds 10–20% on CPU-heavy work. Set opcache.memory_consumption=256 and opcache.jit_buffer_size=64M.
The result
After a full pass on a real 80k-product store: category TTFB from 4,200 ms down to 380 ms, MySQL CPU from 240% down to 18%.
