We were using MySQL like a persistent queue. As soon as a message was spawned, we would send it to downstream SMS gateways and delete them. So essentially that

We were using MySQL like a persistent queue. As soon as a message was spawned, we would send it to downstream SMS gateways and delete them. So essentially that volume didn't use a lot of memory. At stage 3 we had 50% daily active users who would receive on an average of 8 messages per day. So at step 3, we would send 20M messages per day.