I have an object with more than one million records. For same object, I am getting a file for processing every other day. My requirement is to compare all the records(+million) in the file with existing records in the object.(Assume there is a unique key AccountID in the object and file for comparing). If any changes are there like value of any attribute changes, we have to update the existing record.What is the best way to achieve this? .. I know that we can process upto 50 million records using batch. But i have one more concern like how can i fetch more than 50k records in execute method from object(+million) for comparison...?  and also i want to know is there any performance issue if we process this much huge data...?

I have an object with more than one million records. For same object, I am getting a file for processing every other day. My requirement is to compare all the records(+million) in the file with existing records in the object.(Assume there is a unique key AccountID in the object and file for comparing). If any changes are there like value of any attribute changes, we have to update the existing record.What is the best way to achieve this? .. I know that we can process upto 50 million records using batch. But i have one more concern like how can i fetch more than 50k records in execute method from object(+million) for comparison...?  and also i want to know is there any performance issue if we process this much huge data...?