DataStax Academy migrated to a new learning management system (LMS) in July 2020. We are also moving to a new Cassandra Certification process so there are changes to exam bookings, voucher system and issuing of certificates.
Check out the Academy FAQ pages for answers to your questions:
A partitioner determined how the data is distributed across the nodes in the cluster. It is nothing but a hash function that generates a hash token value to a partition key. After that the token is used to assign (Choose the correct one), my guess is number 1. Can you please confirm ?
I'm not sure where you got the information but the question doesn't make sense so allow me to explain.
The partitioner determines which node a partition belongs to based on the token value that is returned by hashing the partition key. For example, for partition key Ramirez:
Murmur3Partitioner( PK = 'Ramirez' ) = -4404190778401486753
Let me use an example cluster to illustrate how tokens and the partitioner work. Here is the output of nodetool ring:
$ nodetool ring community
Datacenter: Cassandra
==========
Address Rack Status State Load Owns Token
3074457345618258602
10.101.33.146 rack1 Up Normal 174.98 KiB 33.33% -9223372036854775808
10.101.33.196 rack1 Up Normal 164.12 KiB 33.33% -3074457345618258603
10.101.36.82 rack1 Up Normal 200.86 KiB 33.33% 3074457345618258602
From this example, here are the range of tokens owned by each node:
10.101.36.82 : -3074457345618258602 to 3074457345618258602
10.101.33.146 : 3074457345618258603 to -9223372036854775808
10.101.33.196 : -9223372036854775807 to -3074457345618258603
-4404190778401486753
This means that the partition with partition key Ramirez belongs to node 10.101.33.196 since the token for Ramirez (-4404190778401486753) is in the range owned by node 10.101.33.196.
When a coordinator gets a write request for a partition with last_name = 'Ramirez', the coordinator will forward the write to node 10.101.33.196. Similarly, when a coordinator gets a read request for the partition with last_name = 'Ramirez', the data will be retrieved from node 10.101.33.196.
To be clear, the partitioner doesn't assign tokens like what you stated in your question:
After that the token is used to assign ...
The token value from the partitioner hash function determines which node a partition is held. Cheers!
5 People are following this question.
