https://zerodha.tech/blog/1-5-million-pdfs-in-25-minutes/
How we generate, digitally sign, and e-mail out 1.5+ million PDFs, as mandated by regulations, in about 25 minutes with a fully self-hosted distributed architecture.
"At Zerodha, many million users login and use our financial platforms every day. Over the recent months, on an average day, 1.5+ million users have been executing stock and derivative transactions. On a volatile day, this number could easily double. After a trading session concludes and all the number-crunching, tallying, and “backoffice” operations are completed—with file dumps received from stock exchanges and other market infrastructure institutions—stock brokers e-mail a digitally signed PDF report called the contract note to every user who transacted on that particular day."