[jimmytucson]

Also your production database is optimized for different workloads than your analytics database.

Usually production is used for fetching and updating a small number of records at a time (think updating a shopping cart), and has strict latency requirements whereas analytics involves reading a large amount of data in columns (think count group by one or two columns), and can be done in batches where the results can get a more and more stale until the next batch runs.

[bingemaker]

How do you batch write the results (say updating shopping carts) when frontend has to reflect whats in the database?

[patmorgan23]

They're talking about moving data between two different back end databases. Your production database optimized for your application/latency.

Then you have your warehouse database that you updated once a day with information from prod.