Speeding up cart to checkout and checkout save actions

1. From personal experience, disable the Mage_Rss module which forces a 'cache clean' 4 times in checkout process -- very expensive if you are using filesystem cache, probably still expensive if you are using database or memcached.

2. CE Only Disable Mage_Downloadable for similar reasons as long as you aren't using Downloadable product, this will speed up checkout and cart actions when you have multiple items in the cart because there are observers on things like checkout_type_onepage_save_order_after which multiply response time by the # of items in cart.

3. Wire up xhprof / xhgui and do some profiling.

• Set your indexes to manual.
• Disable cache tag storage

Both these changes will have a MASSIVE impact on performance as it prevented Magento flushing out caches and re-indexing every time an order goes through.

It comes at a cost though, that content may be stale as a result - stock levels etc.

If you want to solve it the experimental way, there is an extension from the first magento hackathon in munich, german:

https://github.com/magento-hackathon/MongoDB-OrderTransactions

They queue the orders into a mongo db, the idea was, if the mysql-server is free of load to write them back. But I don't know how far this project is ready. Afaik works all the writing, but not the back writing.