The main data access difference between OLAP systems and OLTP systems is how many records on average do you need to access:
- OLAP: most queries need most records (aggregations span large swaths of data)
- OLTP: most queries access just a few records
Also, in OLAP, in many cases, you can live with a single-updater model without much trouble, where OLTP, the strength is to have many concurrent updaters (but mostly non-overlapping).
OLAP - Most queries need an aggregate of records. Generally you do NOT need most records, but simply the records grouped by dimensions per interval (for almost all olap reporting). You do not change the data, you observe it. If you change it, you are not dealing with OLAP data.
OLTP - You are dealing with the ins and outs of people using stuff to do things. You buy something, you check out something, you some way perturb the state of things. This should not require large amount of row lookups in 99.9% of cases.
So the first focuses on analytics and reporting, the second on transactions and performance.
They are not meant to replace each other, they serve different purposes. Some teams may need both.
- OLAP: most queries need most records (aggregations span large swaths of data)
- OLTP: most queries access just a few records
Also, in OLAP, in many cases, you can live with a single-updater model without much trouble, where OLTP, the strength is to have many concurrent updaters (but mostly non-overlapping).