How was FriendFeed’s schema less db faster than pure MySQL?
My answer to How was FriendFeed’s schema less db faster than pure MySQL? on Quora
The principle reason they switched to a schemaless DB was to work around the challenges of having to make schemes changes in MySQL, which can lock the table and take hours if bit days to complete in large tables.
The performance improvement shown in the graph is almost certainly because they almost entirely eliminated joins and complex queries when they switched to the new mechanism. This meant that all it their database traffic was now simple queries, which have much more predictable performance characteristics. MySQL (in fact all databases) are extremely fast at primary key lookups and index scans.