How to decrease the memory consumption of a WordPress site?

The test site requires a lot of memory when viewing some category/archive pages.

I met with the following error messages yesterday:

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to
allocate 48 bytes) in
/var/www/t/wp-includes/load.php on
line 552

Fatal error: Allowed memory size of 209715200 bytes exhausted (tried to
allocate 40 bytes) in
/var/www/t/wp-includes/meta.php on
line 307

The problem was solved by adding the “define(‘WP_MEMORY_LIMIT’, ‘210M’);” line to the wp-config.php file.

But this is not good enough. The production site will have much more data than the test site, which means I have to add the “define(‘WP_MEMORY_LIMIT’, ‘2100M’);” line to the wp-config.php file. And 2100M may not be large enough as the time goes by.

How to decrease the memory consumption of the WordPress site dramatically? Any help is appreciated.