A xoogler has written about Google’s attempt to migrate off MySQL way back in 2000. Apparently, the brilliant minds in Google management decided that “free” software was not as good as commercially available databases, and pushed for a migration to a vendor that the xoogler will not disclose [but I'm guessing Oracle or MSSQL].

The migration was a complete failure and they ended up with MySQL in the end. I bet those Engineers that opposed the migration were snickering in their cubes after the decision was made to stick with MySQL.