Shameless plug here - The author of the article does build time-series databases for a living, and more specifically the Datadog monitoring platform - which will gladly collect your millions of metrics, graph them and alert on them, along with all the events you care to keep :-)

We've been through a number of data stores ourselves, starting with Postgres back in 2010 - then on to Redis + Cassandra before we built our own. But that's a story for another post...

http://datadog.com