Indices speed up the search process in databases and as such, are an essential part of designing databases. In the context of Microsoft Azure Cosmos DB, optimizing these indexes is a critical task that can significantly improve the performance of your applications. This article discusses ways to adjust indexes on the Azure Cosmos DB while preparing for the DP-420 Designing and Implementing Native Applications Using Microsoft Azure Cosmos DB exam.
Understanding Indexing in Cosmos DB
Cosmos DB uses indexing to provide lightning-fast access to data. It automatically indexes all properties in every item in the container without requiring schema or secondary indexes. These indexes take up storage and consume some throughput when you create, update or delete items in your container.
Although Azure Cosmos DB automatically handles indexing, you can adjust these indexes based on your application’s requirements. For example, you might want to exclude some paths from the index to save space, reduce writes, or increase write throughput.
Indexing Modes
The indexing mode in Azure Cosmos DB determines how items are indexed. There are two modes:
- Consistent: With this mode, the index is updated synchronously as writes are made to the container.
- Lazy: This mode is more relaxed regarding the speed at which the index is updated, generally updating the index more slowly than the consistent mode.
Generally, the Consistent mode is advisable due to its strong consistency of indexed data. But, certain situations may benefit from the Lazy mode, especially when dealing with bulk ingestion scenarios.
Indexing Policies
An indexing policy in Azure Cosmos DB is a set of rules that determine how data is indexed in the container. These rules control which data to include or exclude, what indexing mode to use, and other parameters. You can specify this policy at the time of container creation or update it afterwards.
Here’s a simple example of how to define an indexing policy:
{
"indexingMode": "Consistent",
"automatic": true,
"includedPaths": [
{
"path": "/*"
}
],
"excludedPaths": [
{
"path": "/\"propertyToExclude\"/*"
}
]
}
In this policy, every property (“path”: “/*”) is included in the index, except “propertyToExclude”.
Optimizing Indexes
Optimizing indexes involves striking a balance between the query workload requirements and the storage/throughput cost. Few steps you can take to optimize your indexes are:
- Exclude paths that you don’t need: If you don’t plan to query data based on a particular property, exclude it from being indexed to save on storage and throughput utilization.
- Use range indexes for sorting or comparisons: Range indexes are ideal for sorting or comparison operations like “greater than” or “less than” operations.
- Change the index precision: It determines how precisely values are indexed. A precision of -1 will index the property as precisely as possible, however, a lower index precision helps reduce the index overhead at the expense of the precision for some comparison operations.
Conclusion
Proper index management in Azure Cosmos DB can have a direct impact on your application’s performance. By understanding the concepts of indexing mode, policies, and the strategies to optimize them, you can ensure that your application can effectively use resources to deliver superior performance. As you prepare for the DP-420 exam, these core concepts will give you a good grounding in designing and implementing native applications using Microsoft Azure Cosmos DB.
Practice Test
True or False: Indexing can speed up the search operations in Azure Cosmos DB.
- True
- False
Answer: True
Explanation: Indexing provides a way of sorting and accessing data in Azure Cosmos DB which can make operations like searching more efficient.
True or False: In Azure Cosmos DB, you can only have one index for each container.
- True
- False
Answer: False
Explanation: Azure Cosmos DB allows applications to have multiple indexes per container in order to optimize different types of queries.
True or False: Indexes can be automatically created and managed by Azure Cosmos DB.
- True
- False
Answer: True
Explanation: Azure Cosmos DB can automatically manage indexes, as it has an automatic indexing policy by default.
What is the purpose of indexing in Azure Cosmos DB?
- A. To improve write performance
- B. To improve read performance
- C. To decrease storage usage
- D. All of the above
Answer: B. To improve read performance
Explanation: The main purpose of indexing in Azure Cosmos DB is to speed up read operations by providing quick lookup paths to data.
True or False: You do not need to explicitly define indexes for each property in Azure Cosmos DB.
- True
- False
Answer: True
Explanation: Azure Cosmos DB has automatic indexing that by default, indexes all properties.
Which of the following indexing strategies does Azure Cosmos DB support?
- A. Range Index
- B. Spatial Index
- C. Composite Index
- D. All of the above
Answer: D. All of the above
Explanation: Azure Cosmos DB supports different indices including Range index for range queries, Spatial index for spatial queries, and Composite index that can help in querying over multiple fields.
True or False: Indexes in Azure Cosmos DB increase storage costs.
- True
- False
Answer: True
Explanation: Each index created consumes additional storage and hence increases the storage cost.
In what scenarios would you consider adjusting indexes on Azure Cosmos DB?
- A. To optimize for read-heavy workloads
- B. To reduce cost
- C. When certain properties are not regularly queried
- D. All of the above
Answer: D. All of the above
Explanation: Index adjustments can help optimize performance for read-heavy workloads, reduce cost by removing unnecessary indexes, and fine-tune indexing when certain properties are not often queried.
True or False: It’s possible to exclude certain properties from being indexed in Azure Cosmos DB.
- True
- False
Answer: True
Explanation: Azure Cosmos DB allows you to exclude specific paths or properties from being indexed to save on storage and performance costs.
What is the default indexing mode in Azure Cosmos DB?
- A. Consistent
- B. Lazy
- C. None
- D. Unique
Answer: A. Consistent
Explanation: The default indexing mode in Azure Cosmos DB is ‘Consistent’, which means indexes are updated synchronously as data is written to the database.
True or False: Indexing increases write latency in Azure Cosmos DB.
- True
- False
Answer: True
Explanation: Since every write operation must also update the index, indexing can increase the latency of write operations.
Which indexing policy would you use to exclude a property from being indexed in Azure Cosmos DB?
- A. Exclusion policy
- B. Inclusion policy
- C. Exclusion path
- D. Inclusion path
Answer: C. Exclusion path
Explanation: Exclusion paths are used to specify one or more document paths that need to be excluded from indexing.
True or False: You can change the indexing policy of an existing Azure Cosmos DB container without any downtime.
- True
- False
Answer: True
Explanation: Azure Cosmos DB allows indexing policies to be modified for existing containers without causing any downtime.
Which of the following would allow faster queries on a set of properties in Azure Cosmos DB?
- A. Spatial index
- B. Composite index
- C. Range index
- D. None of the above
Answer: B. Composite index
Explanation: Composite index allows faster queries on a set of properties by indexing multiple paths.
True or False: Automatic indexing in Azure Cosmos DB cannot be overridden.
- True
- False
Answer: False
Explanation: Default automatic indexing in Azure Cosmos DB can be overridden by defining custom indexing policies.
Interview Questions
What is the main purpose of adjusting indexes on a database in Microsoft Azure Cosmos DB?
The main purpose of adjusting indexes on a database in Microsoft Azure Cosmos DB is to optimize read and write performance. By indexing the correct properties, you can reduce the query execution time and resource utilization.
Why is it considered a good practice to limit the indexed paths in Azure Cosmos DB?
Limiting the indexed paths in Azure Cosmos DB is a good practice because it helps to improve the write performance and lower the storage cost. Indexing only the necessary paths results in smaller index size and better overall performance.
What are the two types of indexing policies in Azure Cosmos DB?
The two types of indexing policies in Azure Cosmos DB are inclusive and exclusive. The inclusive policy means that the paths you mention will be indexed, while the exclusive policy means the paths mentioned will not be indexed.
How does the Azure Cosmos DB handle indexing by default?
By default, Azure Cosmos DB automatically indexes all properties for all items in your container. This default indexing policy ensures that any query can be served efficiently without requiring the developer to manage indexes.
What is the impact of adjusting precision in the indexing policy of Azure Cosmos DB?
Adjusting precision in the indexing policy can directly affect the storage usage and the performance of Cosmos DB. Increase in precision leads to better query performance but will consume more storage.
True or False: In Azure Cosmos DB, it is necessary to manually adjust the indexes every time data in the database changes.
False. Azure Cosmos DB automatically maintains the indexes as data in the database changes, reducing the need for manual intervention.
What is the use of Spatial indexing in Azure Cosmos DB?
Spatial indexing in Azure Cosmos DB allows efficient querying of spatial data. This type of precision can index geometric point data and help in point-in-polygon queries, nearest neighbor queries, etc.
What is the ‘Indexing Mode’ feature in Cosmos DB and what are its types?
The ‘Indexing Mode’ feature in Cosmos DB allows developers to control how indexing proceeds. The types are ‘consistent’, used for synchronously updating indexes with each write operation, and ‘lazy’, which is more laid-back and shows cost benefits.
Is it possible to have different indexing policies for different partitions in Cosmos DB?
No, it’s not possible to have different indexing policies for different partitions in Cosmos DB. The indexing policy is set at the container level and applies to all items in the container.
How does adjusting the ‘indexing mode’ to ‘lazy’ affect the performance of Cosmos DB?
When the ‘indexing mode’ is set to ‘lazy’, the indexing of your data is not prioritized. This can reduce the latency of write operations and conserve the throughput for read operations. However, the ‘lazy’ mode might cause higher latencies for queries.
How can you manage index transformation for a large dataset in Azure Cosmos DB?
You can manage index transformation for a large dataset in Azure Cosmos DB using the Azure portal, Azure CLI, or SDKs. The portal allows you to change indexing policy, while CLI and SDKs can be used for more complex transformations.
What happens when you exclude a path from indexing in Cosmos DB?
When you exclude a path from indexing in Cosmos DB, the excluded path won’t be indexed and you cannot perform efficient queries against the unindexed path. Although this can reduce storage cost, it may increase query latency.
What are the different types of indexes available in Azure Cosmos DB?
Azure Cosmos DB supports Range and Spatial types of indexes. Range indexes are used for sorting or range queries, while Spatial indexes are used for spatial queries like geometric point data.
How can you change the indexing policy of a container in Azure Cosmos DB?
To change the indexing policy of a container in Azure Cosmos DB, you can use Azure portal, Azure Cosmos DB .NET SDK, Azure Cosmos DB Java SDK, Azure Cosmos DB Python SDK, or Azure Cosmos DB JavaScript SDK.
How does Azure Cosmos DB handle automatic indexing of nested items in an array?
Azure Cosmos DB handles automatic indexing of nested items in an array by retrieving each item as an individual unit. It provides the facility to query over arrays directly, including support for intra-array queries.
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