An autoloaded option that was 400 KB

Every page load unserialising four hundred kilobytes of a plugin’s cached API response, because it had been stored as an autoloaded option.

SELECT option_name, LENGTH(option_value) AS bytes
FROM wp_options WHERE autoload = 'yes'
ORDER BY bytes DESC LIMIT 5;

  some_plugin_catalogue_cache    412,880
  another_plugin_log             188,204
  theme_mods_turkerdev            14,208

-- total autoloaded: 812 KB, on every request

Autoloaded options are read as one query and unserialised in full on every request, so a large one costs on every page including the ones that never touch it. The fix here was update_option with false for autoload plus a transient for the actual caching; the query above belongs in a monthly check, because a plugin update can reintroduce it without any visible change.