After two days, I find something satisfying!!
As you can see in this link ,There are a few parameters :
- having a lot of stores, would affect catalog_url_rewrites
- having a lot of attributes for products would make catalog_attributes or catalog_product_flat so slow.
- having many searchable attributes can affect on catalog_fulltext_search.
As a result, I think paying attention to infrastructure, such as removing unnecessary attributes or stores, or narrowing down the searchable attributes to minimum would help big time!!!
Also there are some server configuration or external indexing and caching tools which can accelerate magento websites. you can see them in the first link I said, or here or maybe there too!
finally, I find out that there isn't any change in indexing, in magento 1.8ce. But there is one big change in magento EE 1.13. So this can be a non-free solution!
Hope these things help you :)