This segment discusses the challenges of managing trillions of transactions and the role of indexes in efficient data retrieval. It explains different types of indexes used by Uber (strongly consistent, eventually consistent, and time range indexes) and their strategies for managing and maintaining these indexes at scale, including backfilling, validation, and decommissioning. This segment details Uber's journey from a monolithic application to a microservice architecture, highlighting the instability and reconciliation issues that arose with growth. It emphasizes the decision to rebuild the payment system from scratch, setting the stage for the explanation of their new approach.This segment explains Uber's implementation of a job order system for managing payments, emphasizing the concept of double-entry accounting and the use of an immutable ledger. It contrasts mutable and immutable databases, explaining why immutability is crucial for financial integrity and how it affects data correction. had two options, process all of this 300 terabyte of data in one go, and then just dump it into their new database, or break down historical data into parts and process them individually and create checkpoints throughout.! the issue with doing number one is that with such a big data,, at any point that it goes wrong,, you have to restart the entire process.. think about installing a software for a long time, and then it just fails.. on the last step,. so they went with option two. And here's how it worked.., a worker boots up and reads the checkpoint of where the process needs to be started from.. it then goes to cold storage, where the data lives and processes this data and moves it to the new database, and then updates the checkpoint to say that the partition it filled out is successful. So it doesn't get repeated., and it then stores this in a metadata database, so that other simultaneous workers don't work on the same ones.., And this process only allowed that data to take a couple of weeks and saved on a lot of money.. have our historical