One of the foremost considerations is implementing effective design partitioning for workloads that require multiple partition keys. This task becomes crucial when dealing with large data sets to ensure practices related to data management are maintained in a full-throttle and economic way.
What is Design Partitioning?
Design partitioning in Cosmos DB is a manageability and scalability strategy that involves splitting data into smaller manageable parts (called partitions) based on a partition key. Its main objective is to distribute a collection’s documents into distinct partition sets. This is important because it allows applications to be highly responsive and available, even when managing massive amounts of data across various geographical regions.
When to use Multiple Partition Keys?
Handling multiple partition keys is vital for scenarios where data in Cosmos DB needs to be divided according to more than one attribute, mainly when you want to manipulate each part of the data separately or want the queries to be more efficient. For example, consider an e-commerce application where the dataset contains both user and product information. In this case, you may want the user data divided according to UserID and the product data according to ProductID. Thus, it requires a scheme of multiple partition keys.
Implementing Multiple Partition Keys in Azure Cosmos DB
Currently, Azure Cosmos DB does not support having multiple partition keys for the same data container. However, this does not mean that databases requiring multiple partition keys cannot be implemented effectively. In this case, Composite Partition Key comes to the rescue.
Composite partition keys include multiple attributes to create a logical single partition key. This concept allows us to store related items in the same logical partition by combining multiple properties in our model.
For example, consider a simple document model for messages in a chat room:
{
"chatroom": "Azure",
"sentAt": "2021-09-17T12:00:00",
"messageBody": "Hello!",
"sender": "John"
}
If both `”chatroom”` and `”sentAt”` are chosen as composite keys, all the messages in the same chat room and sent at the same hour are stored into the same logical partition.
Points To Consider While Choosing Partition Key
While multiple partition keys in data containers are not directly supported, you can fully take advantage of multiple partition keys by carefully choosing your partition key.
Here are a few things to consider:
- A high cardinality is a must. This means there should be a wide range of possible values.
- The key should distribute write and read operations evenly across all partitions.
- To enable multiple operations to be performed atomically and at a low latency, key values belonging together should stay together.
Conclusion
Design partitioning is crucial for creating scalable and performant applications using Microsoft Azure Cosmos DB. However, while using multiple partition keys can help you create more efficient databases, bear in mind that a partition key should be chosen carefully to ensure optimal performance.
Practice Test
True or False: In Azure Cosmos DB, all items with the same partition key are stored together.
- True
- False
Answer: True
Explanation: Azure Cosmos DB uses the partition key to distribute the data and workload across multiple partitions.
What type of partition keys can be used in Azure Cosmos DB?
- A. Only a single partition key
- B. Multiple partition keys
- C. No partition keys
Answer: B. Multiple partition keys
Explanation: Azure Cosmos DB amends data across various partitions and allows multiple partition keys for adding even distribution of the workload.
Can you use a composite index to increase query performance with multiple partition keys in Azure Cosmos DB?
- A. Yes
- B. No
Answer: A. Yes
Explanation: Using a composite index can enhance the performance of a query with multiple partition keys by reducing the indexing overhead.
True or False: A collection with multiple partition keys is restricted to a single Azure region.
- True
- False
Answer: False
Explanation: The distribution of data in Azure Cosmos DB is not bound to any region.
Is it possible to repartition Cosmos DB data after it has been created?
- A. Yes
- B. No
Answer: B. No
Explanation: Once a collection has been created, it is not possible to change or repartition the data without creating a new collection and moving the data.
Larger partition key values result in:
- A. Improved performance
- B. Deteriorated performance
- C. No impact on performance
Answer: B. Deteriorated performance
Explanation: Larger partition key values may lead to hot partitions which can impact performance negatively.
True or False: The ideal partition key for a Cosmos DB collection will create even data distribution.
- True
- False
Answer: True
Explanation: The optimal partition key is meant to yield a uniform distribution of data across all partitions.
How many partition keys can a single document in Cosmos DB have?
- A. One
- B. Two
- C. More than two
Answer: A. One
Explanation: Each document in Cosmos DB can have only a single partition key.
In Azure Cosmos DB, partitions are spread across:
- A. Logical partitions
- B. Physical partitions
- C. Single partition
Answer: B. Physical partitions
Explanation: Cosmos DB distributes logical partitions across physical partitions.
The same partition key must be used for all items in a container.
- A. True
- B. False
Answer: B. False
Explanation: Different items in a container can have different partition keys.
A partition key is responsible for distributing the:
- A. Workload
- B. Data
- C. Both data and workload
Answer: C. Both data and workload
Explanation: A partition key in Azure Cosmos DB is used for distributing both data and workload evenly.
True or False: The partition keys in Azure Cosmos DB are case sensitive.
- True
- False
Answer: True
Explanation: In Azure Cosmos DB, the partition key values are case sensitive.
When partitioning for workloads, what’s the maximum amount of storage per partition key value in Cosmos DB?
- A. 20 GB
- B. 50 GB
- C. 10 GB
Answer: A. 20 GB
Explanation: A single partition key value is able to hold up to 20 GB of data in Azure Cosmos DB.
Should you include every property of the documents as a partition key?
- A. Yes
- B. No
Answer: B. No
Explanation: Including every property as a partition key can lead to unnecessary complexity and potential performance issues.
True or False: Understanding the application’s request patterns is not important for choosing the correct partition key.
- True
- False
Answer: False
Explanation: Understanding the application’s request patterns is crucial to make a decision on the suitable partition key that will effectively distribute the workload.
Interview Questions
What is design partitioning in Microsoft Azure Cosmos DB?
In Microsoft Azure Cosmos DB, design partitioning is a method used to distribute data across many physical partitions. It scales throughput and storage by spreading data and traffic for a container across a number of replicas.
What’s the role of partition keys in Azure Cosmos DB?
Partition keys are responsible for data distribution to achieve scale-out. In Azure Cosmos DB, every item in a container has a unique identifier composed of two properties: an id and a partition key. The combined value forms the item’s index and must be unique within a container.
Why might a workload require multiple partition keys?
A workload might require multiple partition keys when it needs to organize data in different ways according to varied access patterns. Splitting the data into multiple partition keys allows for more efficient retrieval and update of data.
What is the partition key range in Azure Cosmos DB?
Partition key range in Azure Cosmos DB is the range of partition key hashes that a physical partition maintains. A single physical partition is assigned to manage multiple partition key ranges.
How does Azure Cosmos DB determine the partition for a specific data item based on its partition key?
Azure Cosmos DB uses a hash-based partitioning system. It hashes the partition key value of an item and distributes it to a specific partition based on the hash value.
What is the maximum storage limit for each logical partition in Azure Cosmos DB?
Each logical partition in Azure Cosmos DB has a storage limit of 20 GB.
How can I change the partition key in Azure Cosmos DB after data has been created?
In Azure Cosmos DB, you can’t change or update the partition key once the data has been created. If you want to change the partition key, you have to create a new container with the desired partition key and migrate the data.
Are there any restrictions on choosing a partition key in Azure Cosmos DB?
Yes, Azure Cosmos DB has a few restrictions to consider when choosing a partition key. It should distribute workload evenly across all partitions, and you should avoid choosing a key with a small number of possible values or a strong skew in the distribution of request rates.
How can query performance be optimized with the use of partition keys in Azure Cosmos DB?
Query performance can be optimized in Azure Cosmos DB by issuing the query against a single partition key value. This reduces the scope of the search and consequently speeds up the response time.
Can you use composite partition keys in Azure Cosmos DB?
Yes, Azure Cosmos DB allows the use of composite partition keys. A composite partition key is formed by concatenating values from multiple properties within your items. This helps when your workload can’t be effectively partitioned using a single property.
Why may hot partitioning occur in Azure Cosmos DB?
Hot partitioning happens when a disproportionate volume of requests are directed to a single partition. This usually occurs if a partition key is poorly chosen, causing uneven distribution of requests or storage.
How can I mitigate hot partitioning in Azure Cosmos DB?
You can mitigate hot partitioning in Azure Cosmos DB by choosing a partition key which uniformly distributes data. If hot partitioning occurs, redistributing the data by choosing a new, more uniformly-distributed partition key is an option.
How should you select the partition key to ensure maximum scalability and performance?
To ensure maximum scalability and performance in Cosmos DB, you should choose a partition key that distributes your workload evenly across all partitions. The key should also match the most common querying pattern to optimize read functionality.
What is the best practice to manage workloads requiring multiple partitions keys?
The best practice is to firstly understand the data access patterns and then model the partition key based on these patterns to ensure the data and requests are evenly distributed across the partitions.
What happens when a logical partition in Azure Cosmos DB exceeds the storage limit?
When a logical partition exceeds the storage limit, you’ll receive a HTTP 413 error indicating “Request Entity Too Large” and you’ll have to either delete data or move some of it onto a different logical partition with a different partition key.
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