I was once told by an IT manager of a supermarket chain, that no db was able to handle the high-volume of transaction they had during the peak hours. It was ane

I was once told by an IT manager of a supermarket chain, that no db was able to handle the high-volume of transaction they had during the peak hours. It was anecdotal without any hard proof and he did not want to get to the details as it will reveal their inner workings. They have 50 branches with each store having 30 counters. Any truth to that?