- DataStax Enterprise (DSE) database treats each new row as an upsert.
- During a write, DSE Cassandra adds each new row to the database without checking on whether a duplicate record exists.
- Most DSE installations store replicas of each row on two or more nodes. Each node performs compaction independently. This means that out-of-date versions of a row have been dropped from one node, they may still exist on another node. This is why the database performs another round of comparisons during a read process.
Note: Some database operations may only write partial updates of a row, so some versions of a row may include some columns, but not all. During a compaction or write, the database assembles a complete version of each row from the partial updates, using the most recent version of each column.