Does an UPDATE become an implied INSERT

Question

For Cassandra, do UPDATEs become an implied INSERT if the selected row does not exist? That is, if I say

 UPDATE users SET name = "Raedwald" WHERE id = 545127 

and id is the PRIMARY KEY of the users table, and the table has no row with a key of 545127, will that be equivalent to

 INSERT INTO users (id, name) VALUES (545127, "Raedwald") 

I know that the opposite is true: an INSERT for an id that already exists becomes an UPDATE of the row with that id. Older Cassandra documentation talked about inserts actually being "upserts" for that reason.

I'm interested in the case for CQL3, Cassandra version 1.2+.

Answer 1

Yes, for Cassandra UPDATE is synonymous with INSERT, as explained in the CQL documentation where it says the following about UPDATE:

Note that unlike in SQL, UPDATE does not check the prior existence of the row: the row is created if none existed before, and updated otherwise. Furthermore, there is no mean to know which of creation or update happened. In fact, the semantic of INSERT and UPDATE are identical.

For the semantics to be different, Cassandra would need to do a read to know if the row already exists. Cassandra is write optimized, so you can always assume it doesn't do a read before write on any write operation. The only exception is counters (unlessreplicate_on_write = false), in which case replication on increment involves a read.