One Million SKUs Import - Bulk insert\update

Hello,

We have a client with about 1 million SKUs in their catalog.

The challenge we are facing is how we can import/update this huge number of products in most effiicent way.

With initial running of our custom product import tool in the development environment, it takes 1 second to insert\update 2 SKUs. This means we need about 6 days to update the catalog :)

I will be optimistic and say that it would take 1 second to update 4 SKUs on production. Still, we will need about 3 days to update the whole catalog!

Our custom tool uses IContentRepository to create/update products.

We do not use CatalogEntryDto but VariationContent.

My questions are:

1. Is there any other approach that would save time for importing such a huge catalog?
2. Is there anyway we can do a bulk update for the catalog using IContentRepository?

Thanks!