Snowflake stores data in micro partitions between 5 and 500 megabytes. Every change (UPDATE, INSERT or DELETE) to a micro partition means that Snowflake must replace the entire micro partition. Making changes in an existing micro partition is impossible because Amazon S3 does not implement this. Micro partitions are created when loading an empty table. If data is added, new micro partitions are created. If a change through an UPDATE or DELETE statement is necessary, Snowflake deletes the existing micro partition and replaces it with a new one. I assume that micro partitions will not be deleted immediately but will remain available for the Time Travel feature for a while.