For a website that should allow searching based on a few filters on about 100 millions records, is it good enough to pick Solr for searching?
The website would be written in C#, (asp.net mvc), the backend database with user data and shopping cart should be SQL Server 2008R2. Does it scale ok for 10 million users?
Other stuff that should be used: Memcached, HAProxy probably…
I have not directly worked with solr, but it is highly scalable and I have worked at a company that used it for asp.net webform sites wtih extremely high traffic (e.g. a national newspaper, online magazines). Yes, it is based in Java so there would definitely be a mismatch in technology, but it scales very well with replication and ‘sharding’ technology. see wikipedia.
It’s also fairly stable – it was created in 2004. You can see a number of very large traffic sites that use it here