By Sachin Kumar Every transaction has an isolation level to maintain data consistency. There are multiple types of isolation levels. The list and definition of isolation levels is at this link. Read the linked article carefully because the isolation that you choose depends upon your data consistency and integrity or any other business requirements.
For large analytics data you should use snapshot isolation with column store index (clustered or unclustered).
And few of the isolation levels has to be turned on (e.g. snapshot).
The default isolation level in MSSQL is Read Committed.
Cheers and Peace out!!!