Our store has more than 30K products and most of them are child product and not visible individually. How can I prevent to add new url rewrite for these products? I mentioned how can we manage url rewrite proccess, e.g I want to not add url rewrite for a particular products, for example disabled, not visible, not categorized products? Anybody have some hints? Thanks.
The magento url_rewrite system is quite problematic. It has bugs which let the table grow on every reindex and its designed for comfort, so it includes rewrites for not visible products.
Beside the bug, most of work you want to do on it is very shop dependend, as it mostly results in a reduced feature set.
If you want to change, you need to rewrite the Mage_Catalog_Model_Url Model.
There for example you could rework the _refreshProductRewrite function to jump over it, if the current product is not showed anyway.