Cassandra Data Modelling
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The document presents a detailed overview of data modeling in Apache Cassandra, highlighting the importance of keys such as primary and partition keys for data distribution and organization. It emphasizes the need to model data around query requirements instead of relationships, advocating for a single table per query pattern for optimization. Practical examples are provided, including schema designs for user posts and gym information, demonstrating effective data structuring for efficient retrieval.
Cassandra Data Modelling
- 1. Cassandra Data Modeling Presented By: Charmy Garg Software Consultant Knoldus Inc.
- 2. 01 Keys in Cassandra 02 Basic Goals 03 Model your own Queries 04 Applying Rules: Examples 05 Glance at Use cases Our Agenda
- 3. What is Apache Cassandra?
- 4. Cassandra vs Relational Cassandra Data Model Relational Data Model Keyspace Database Column family Table Partition key Primary Key Column Name/Key Column Name Column value Column value
- 5. Equivalent to the Partition Key in a single-field-key table (i.e. Simple). Just any multiple-column key. Responsible for data distribution across your nodes. Responsible for data sorting within the partition. 1 2 3 4 Primary Key Composite Key Partition Key Clustering Key “Keys to Recall for Cassandra Data Modeling”
- 6. Primary Key
- 8. Clustering Key & Partition Key
- 9. How Cassandra organizes data
- 11. Non-Goals Minimize Data Duplication Minimize the Number of Writes As Cassandra is a distributed database, so data duplication provides instant data availability and no single point of failure. Cassandra is optimized for high write throughput, and almost all writes are equally efficient.
- 12. 2 1 4 1Spread data evenly around the cluster Rows are spread around the cluster based on a hash of the partition key, which is the first element of the PRIMARY KEY. So, the key to spreading data evenly is this: pick a good primary key. Minimize the number of partitions read Partitions are groups of rows that share the same partition key. When you issue a read query, you want to read rows from as few partitions as possible. Basic Goals
- 13. Model Your Data The way to minimize partition reads is to model your data to fit your queries. Don't model around relations. Don't model around objects. Model around your queries. Here's how you do that: Determine what queries you want to support Create table according to your queries Step 2Step 1
- 14. www.website.com Try to determine exactly what queries you need to support. This can include a lot of considerations that you may not think of at first. For example, you may need to think about: ● Grouping by an attribute ● Ordering by an attribute ● Filtering based on some set of conditions ● Enforcing uniqueness in the result set Changes to just one of these query requirements will frequently warrant a data model change for maximum efficiency. Step 1: Determine What Queries to Support
- 15. www.website.com Use one table per query pattern. If you need to support multiple query patterns, you usually need more than one table. If you need different types of answers, you usually need different tables. This is how you optimize for reads. Remember, in Cassandra data duplication is okay. Many of your tables may repeat the same data. Step 2: Create table for Queries
- 16. Applying the Rules: Examples
- 17. c Example 1: Table Music Playlist In the example, table Music Playlist, ● SongId is the partition key, and ● SongName is the clustering column
- 18. c Example 1: Table Music Playlist In the example, table Music Playlist, ● SongId and Year are the partition key, and ● SongName is the clustering column.
- 19. Glance at Use Cases
- 20. Use Case 1 Suppose that we are storing Facebook posts of different users in Cassandra. Query: Fetch the top ‘N‘ posts made by a given user. We require user_id, post_id and content as fields. The Cassandra table schema for this use case would look like: Stores all data for a particular user on a single partition as per the above guidelines. Using the post timestamp as the clustering key will be helpful for retrieving the top ‘N‘ posts more efficiently.
- 21. Use Case 2 Suppose that we are storing the details of different partner gyms across the different cities and states of many countries. Query: Fetch the sorted gyms for a given city. We require country_code, state, city, gym_name and opening_date as fields. The Cassandra table schema for this use case would look like: Also, let’s say we need to return the results having gyms sorted by their opening date. Store the gyms located in a given city of a specific state and country on a single partition and use the opening date and gym name as a clustering key.
- 22. References Baeldung - Cassandra Data Modeling Guru99 - Data Modeling rules in Cassandra Simple Learn - Cassandra Data Modeling Datastax - Cassandra Data Modeling rules
- 23. Q&A Please email your queries at charmy.garg@knoldus.in