I've got an OpenCart website (https://www.haarhuis.shop) which took about 60 seconds to completely load any page of both the customer and admin section. I've managed to bring this down to about 15-20 seconds by increasing the memory_limit in the php.ini file, cleaning up the template files and creating indexes in the MySQL database tables, but 15-20 seconds is still way too much waiting time.
I've used several dev tools to find out what the problem can be but I can't find the solution. 90% of the loading time consists of 'Waiting (TTFB)' time. See the table below:
Event When Time Sum
Redirect 0 0 0
DNS 18 0 0
Connect 18 20 20
TTFB 38 18119 18139
Response 18156 520 18659
DOM 18321 542 19201
Interactive 18793 0 -
Content 18793 36 -
The server has 3 CPU's and 6GB of memory, which should be more than enough. There's a constant usage of about 8% of the memory, and when someone loads the page this will go up to about 40%. The memory_limit is set to 6G, so the problem doesn't lay with the server.
I've debugged the OpenCart source (starting in index.php) and most time (~10 seconds) comes from the last line, start('catalog');(or start('admin'); in the admin directory). The other 5 seconds come from
// VirtualQMOD
require_once('./vqmod/vqmod.php');
VQMod::bootup();
Further debugging shows that the startup/router takes the most time in system/engine/router.php. Now my debugging knowledge stops over here, so is there anyone who can help me out making the website faster?
Could it be that you haven't created the correct database indices as described here: https://www.antropy.co.uk/blog/opencart-1-5-site-search-very-slow/
Or could it be the bug with the file /vqmod/checked.cache.php getting too big as described here: https://forum.opencart.com/viewtopic.php?t=165423
(There are solutions for each issue at the links.)