Doğru yere doğru indexleri eklemelisiniz. Yanlış indexleme veritabanında yük/şişme oluşturur.

Aşağıda ki indexleri projelerimde kullanıyorum. Kullanan arkadaşlar sorumluluğu bana yüklememek kaydıyla faydalanabilirler.

ALTER TABLE oc_address ADD UNIQUE INDEX (address_id);
ALTER TABLE oc_address ADD INDEX (address_id);
ALTER TABLE oc_cart ADD UNIQUE INDEX (cart_id);
ALTER TABLE oc_cart ADD INDEX (customer_id);
ALTER TABLE oc_cart ADD INDEX (session_id);
ALTER TABLE oc_customer_wishlist ADD INDEX (customer_id);

ALTER TABLE oc_category ADD UNIQUE INDEX (category_id);
ALTER TABLE oc_category ADD INDEX (parent_id);
ALTER TABLE oc_category ADD INDEX (category_id,top,status,sort_order);
ALTER TABLE oc_category_description ADD INDEX (category_id,language_id,name);
ALTER TABLE oc_category_description ADD INDEX (category_id,language_id,name);
ALTER TABLE oc_category_path ADD INDEX (category_id);
ALTER TABLE oc_category_to_store ADD INDEX (category_id,store_id);
ALTER TABLE oc_category_to_layout ADD INDEX (category_id,store_id,layout_id);

ALTER TABLE oc_language ADD UNIQUE INDEX (language_id);
ALTER TABLE oc_language ADD INDEX (name,code,status);

ALTER TABLE oc_product ADD UNIQUE INDEX (product_id);
ALTER TABLE oc_product ADD INDEX (status,sort_order,date_available,quantity);
ALTER TABLE oc_product_description ADD INDEX (product_id,language_id);
ALTER TABLE oc_product_description ADD FULLTEXT INDEX (name,description);
ALTER TABLE oc_product_image ADD INDEX (product_id);  

ALTER TABLE oc_seo_url ADD INDEX (query,language_id,store_id);

ALTER TABLE oc_session ADD FULLTEXT INDEX (session_id);

ALTER TABLE oc_setting ADD INDEX (store_id,code,`key`);
ALTER TABLE oc_setting ADD INDEX (code);
ALTER TABLE oc_setting ADD INDEX (`key`);