Data Modeling Best Practices¶

These additional topics provide a broader perspective on data modeling, query design, schema design, and best practices when working with ScyllaDB or similar distributed NoSQL databases.

Partition Key Selection

Choose your partition keys to avoid imbalances in your clusters. Imbalanced partitions can lead to performance bottlenecks, which impact overall cluster performance. Balancing the distribution of data across partitions is crucial to ensure all nodes are effectively utilized in your cluster.

Let’s consider a scenario with poor partition key selection:

CREATE TABLE my_keyspace.messages_bad (
  user_id uuid,
  message_id uuid,
  message_text text,
  created_at timestamp,
  PRIMARY KEY (user_id, message_id)
);

In this model, the partition key is chosen as user_id, which is a globally unique identifier for each user. This choice results in poor partition key selection because it doesn’t distribute data evenly across partitions. As a result, messages from popular users with many messages will create hot partitions, as all their messages will be concentrated in a single partition.

A better solution for partition key selection would look like:

CREATE TABLE my_keyspace.messages_good (
  message_id uuid PRIMARY KEY,
  user_id uuid,
  message_text text,
  created_at timestamp
);

In this improved model, the partition key is chosen as message_id, which is the unique identifier for each message. This choice results in even data distribution across partitions because each user’s messages are distributed across multiple partitions. Popular users with many posts won’t create hot partitions, as their messages are distributed across the cluster. This approach ensures that all nodes in the cluster are effectively utilized, preventing performance bottlenecks.