One million new records a month is less than one new record a second. Ten million new records a month is almost four new records a second (slightly more than four if the month is February!). That is not a challenging level of performance for any database, relational or otherwise.
It is indeed the millions-per-hour order of magnitude where things get interesting.
Re:Guide to MongoDB for startups
by jasonmccay on Saturday March 22, 2014 @11:55AM
(#7449506)
Man, I need to go break the news to our customers that are successfully inserting millions of documents per hour (and their apps running nicely ... probably an app you have used) to inform them that, in all reality, they are "failing miserably."
They'd be shocked(!) at the news. ;)
It fails miserably in various ways when processing millions of new records per hour. On a very large scale MongoDB is unusable, but it is fine for problems 2-3 orders of magnitude smaller, so long as the data is not mission-critical.