Cassandra Token or Hash Values - cassandra

Question

I have a student table in Cassandra with column named StudentId as primary key. Can two values from this column have same token/hash value?
Table structure
|-----------|-------------|
| StudentId | Primary Key |
| FName | |
| FName | |
|-----------|-------------|

Answer 1

So I think that I get what you're trying to ask here. When determining data distribution, the partition key (first part of the PRIMARY KEY) is hashed to obtain a token. That row is then written to the node(s) responsible for that particular token range.
As for having the same hash value, it is important to note that PRIMARY KEYs in Cassandra are unique. Therefore, to have the same hashed token value, rows would have to have identical partition keys, which is not possible.
To demonstrate this, I have re-created your table and INSERTed a few rows:
CREATE TABLE student (
studentid TEXT PRIMARY KEY,
fname TEXT,
lname TEXT);
INSERT INTO student (studentid, fname, lname) VALUES ('aploetz','Aaron','Ploetz');
INSERT INTO student (studentid, fname, lname) VALUES ('aploetz','Avery','Ploetz');
INSERT INTO student (studentid, fname, lname) VALUES ('janderson','Jordy','Anderson');
INSERT INTO student (studentid, fname, lname) VALUES ('mgin','Micah','Gin');
Now I will query that table, utilizing the token function on the partition key (studentid):
SELECT token(studentid),studentid,fname,lname FROM student ;
system.token(studentid) | studentid | fname | lname
-------------------------+-----------+-------+----------
-5626264886876159064 | janderson | Jordy | Anderson
-1472930629430174260 | aploetz | Avery | Ploetz
8993000853088610283 | mgin | Micah | Gin
(3 rows)
Notes:
In using the token function on the partition key, I can see the hashed token values, thus I can determine which node(s) in the cluster will contain this data.
The first two students I inserted had different names, but they ended up with the same studentid of aploetz. As PRIMARY KEYs are unique, only one persisted.
The row for Avery Ploetz "won," as it was written last.
Let me know if you require any further explanation, but I hope this helps to answer your question.