What is the best way to read data from the database?

Question

Python

We write the transfer of data from one database to another. We use pyodbc.
There is a lot of data, tables are long. We decide with a colleague how best to read the data.
1. do a fetchall
2. cycle through the cursor
Which way to read is faster? more reliable? save on memory?

Answer 1

read obviously with the cursor
insert - beam

Answer 2

I think that in the first place it is worth optimizing a heavier record. Here bulk insert is a panacea.
By the way, I don’t exclude at all the crasy option of subtraction into a text file in the form of sql insert blocks and their subsequent execution through bulk