How do I update the database in the most efficient manner?
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I am building a price comparison site that holds about 300.000 products and several hundred clients.

On a daily basis the site needs updating of prices and vendor stock availability.

When a vendor needs updating I was thinking about deleting all the vendor information and then pulling and inserting a new - each time.

Doing this I don't have to worry about a vendor deleting a product. In a simple way I would get a new set of data each day.

On the other hand I need to keep the autoincrement counter in check and it seems a waste to delete everything from a vendor if he has only updated prices on 3 products in his entire warehouse.

But updating has its disadvantages too. I still have to read out all data and compare each and every product price/availability to the data from the vendor, one product at a time. Also it's more complicated to notice products that gets deleted by the vendor.

How do I achieve updating in the most efficient and easy way?
