Which database to choose and the data update algorithm?

Question

SQL

Help me choose a database for a web project.
There is one main accounting system, information will be periodically uploaded from it.
In principle, it will be unloaded in any format (in xml / json / csv, etc.) and structure, this is not a problem.
- a table with information about goods (name, description and other fields)
- prices (two fields - key-value)
- balance (two fields - key-value)
Product data will be uploaded as it changes in the main accounting system.
But prices and quantities will be uploaded immediately for all products and often, the size is somewhere around 1 million records.
Problem:
- need to load into database very fast
- when loading, the table should not be blocked (well, so that the web application would access this data and get a normal result, not 0 or whatever)
For now, everything is spinning on MS SQL Server, tables with data are loaded into memory, when loading bulk insert from a text file is used (data loading is instantaneous) and everything seems to be fine. But I want to get away from MS SQL and perhaps there are more interesting options.

Answer 1

If you want to go for a free solution, then just take PostgreSQL.
NoSQL solutions have a problem with accessibility. Some with relevance. In MongoDB, for example, when a transaction is successful, you will get old data for a while.
And if you specify a flag that you do not need such behavior, then there will be problems with readability.