Someone more knowledgeable about Rails can pitch in, but I believe in the absence of any connection management code, Rails will check out one connection per req

Someone more knowledgeable about Rails can pitch in, but I believe in the absence of any connection management code, Rails will check out one connection per request the first time it is used? And checkin after the request terminates? If that is the case, wouldn't the number of simultaneous requests effectively be capped at the database pool size for DB heavy applications?