For a heavy user content website with user profiles, live feeds, photo /video/content sharing, etc what DB to use, and what DB engine? Ofcourse Oracle/Microsoft sql are out because they are not free (or cheap). I am using MySQL with MyISAM but that will run into performance issues on a social site. Even using InnoDB may not help performance. So firstly which DB is better to use and which engine - starting from Free to paid?
Main concern is with live feeds performance, plus there is lots of data tracking and mining with analytic.
Since this is a startup - hardware costs are limited so no hardware farm here to support performance, hence seeking a decent alternative for the first 2 years atleast.
If your userbase is large enough to require a high-performance DB, your bandwidth and storage charges will not be cheap; why skimp on the database?
MS SQL has free and/or cheap editions which are performance-inhibited. I always start with them, and if the site takes off, I upgrade. Probably Oracle offers something similar.
Edit: I should have said at the start that you're unlikely to outgrow MySQL anytime soon, and that this whole question might be a case of premature optimization.