I see. I would suggest you explore the following:
1. CitusDB (an offshoot of postgres with high ingestion rate, cloudflare used it)
2. Druid.io (popular in ad-tech)
3. Linkedin Pinot (uber uses it for similar use-cases)
4. memSQL (used in ad-tech)
Thanks for the pointers but I am planning to revolve more around AWS ecosystem so that I have less ops burden of managing servers + regionalization becomes easy.