Indexing in Cosmos DB is automatic – all the documents, by default, are indexed. This ensures that there are no laborious manual index management tasks needed from your side and speeds up the process of sorting and querying significantly. The Indexing Policy in Cosmos DB handles indexing of data in your containers. While the system indexes every property within a document in the container, you have the flexibility to customize it by either including or excluding certain properties.
Composite Indexing
Composite indexing stands as a noticeable feature in Cosmos DB indexing policies. Unlike single field indexes, composite indexes index multiple fields in a document, thereby providing an efficient way to optimize the query engine performance. Using composite indexes, you can cater SQL ORDER BY queries effectively and boost performance in case of complex filtering.
Implementing a Composite Index
In Cosmos DB, implementing composite indexing involves defining the composite index inside the indexing policy for a container. Following is a representation of an indexing policy with a composite index in JSON format:
{
“indexingMode”: “consistent”,
“automatic”: true,
“includedPaths”: [
{
“path”: “/*”
}
],
“excludedPaths”: [ ],
“compositeIndexes”:[
[
{
“path”:”/field1″,
“order”:”ascending”
},
{
“path”: “/field2”,
“order”:”descending”
}
]
]
}
In this policy, a composite index is defined on ‘/field1’ (in ascending order) and ‘/field2’ (in descending order). A crucial aspect to ensure while forming the composite index path is the sequence of fields; the order in this path directly corresponds to Order By clause in queries.
Considerations and Limitations
While composite indexes instill power and flexibility in data operations, a thoughtful approach to implementing them is beneficial. Composite indexes can fall heavy on storage and can impact the Write RU/s (Request Units per second). Therefore, it’s advised to implement composite indexes only on queries that specifically require them for optimization.
Please note, Cosmos DB gives a limitation of 32 paths for a composite index. Additionally, it doesn’t allow mixing range and spatial data types in the same composite index.
Conclusion
In essence, composite indexing is a potent tool in Cosmos DB that acts as a performance catalyst for certain types of queries. However, it should be used judiciously, keeping in mind its impact on storage and write performance. As you prepare for the professional role in designing and implementing native applications using Microsoft Azure Cosmos DB, the understanding and proficiency of managing composite indexes could be a significant skill up your sleeve.
Practice Test
True or False? Azure Cosmos DB composite indexes do not require JSON syntax.
- Answer: False.
Explanation: The index policy for a composite index in Azure Cosmos DB is specified in JSON syntax.
What is the first step in implementing a composite index in Azure Cosmos DB?
- A) Creating a new container.
- B) Defining an index policy.
- C) Uploading the data.
- D) Writing a query.
Answer: B) Defining an index policy.
Explanation: The first step in implementing a composite index is defining an index policy.
True or False? Composite indexes in Azure Cosmos DB provide automatic indexing and tunable consistency.
- Answer: True.
Explanation: Azure Cosmos DB offers automatic indexing, which means you don’t need to deal with index management or schema updates, and tunable consistency levels, including strong, bounded staleness, session, eventual, and consistent prefix.
What is the maximum number of distinct fields that can be included in a composite index in Azure Cosmos DB?
- A) 8
- B) 10
- C) 12
- D) 20
Answer: B) 10
Explanation: A composite index path can include up to 10 distinct fields.
True or False? Composite indexes can boost the performance of both simple and complex queries in Azure Cosmos DB.
- Answer: True.
Explanation: Composite indexes can speed up both single-property queries AND complex queries that involve sorting results or filtering on multiple properties in Cosmos DB.
Which of these is NOT a principle when designing composite indexes in Azure Cosmos DB?
- A) Minimize the number of fields in the index
- B) Include as many fields as possible in the index
- C) Ensure the index fields match the query as closely as possible
- D) Keep the cardinality and selectivity of the fields in mind
Answer: B) Include as many fields as possible in the index
Explanation: It’s not advisable to include as many fields as possible in the index. Instead, you should minimize the number of fields in the index and ensure they match the query as closely as possible.
True or False? A composite index can only be defined for a single container in Azure Cosmos DB.
- Answer: True.
Explanation: Composite indexes are defined at the container level. Thus, a composite index applies only to the container it is defined on.
In Azure Cosmos DB, by default, the indexing policy is set to what mode?
- A) None
- B) Consistent
- C) Lazy
- D) Automatic
Answer: D) Automatic
Explanation: By default, Azure Cosmos DB sets the indexing mode to ‘Automatic’.
What is the ultimate benefit of implementing a composite index in Azure Cosmos DB?
- A) Faster queries
- B) More storage
- C) No need for maintenance
- D) All of the above
Answer: A) Faster queries
Explanation: The primary purpose of implementing a composite index is to increase the speed and performance of queries.
True or False? To use composite indexing, you need to modify the query.
- Answer: False.
Explanation: Azure Cosmos DB automatically utilizes composite indexes once implemented. You don’t have to rewrite or modify your queries.
Interview Questions
What is a composite index in Microsoft Azure Cosmos DB?
A composite index in Azure Cosmos DB is a special type of index that allows you to sort data by more than one property. It enables applications to perform complex queries efficiently.
How do you define a composite index in Cosmos DB?
You can define a composite index in Cosmos DB using the “compositeIndexes” field in the indexing policy. It includes the names of the paths and the sort order for each path.
What is the purpose of implementing a composite index in Cosmos DB?
Implementing a composite index in Cosmos DB improves the performance of queries that involve sorting and filtering data on multiple properties by reducing the indexing storage overhead and enabling efficient execution.
Are there any limitations when you implement a composite index in Cosmos DB?
Yes, there are limitations when implementing a composite index in Cosmos DB. You can have a maximum of 32 paths in a composite index, and the total length of all paths must be less than or equal to 1023 characters.
Can I update the composite index after it has been created in Cosmos DB?
Yes, you can update the composite index in Azure Cosmos DB. However, need to be careful as updating the index might lead to increased indexing time.
What JSON path syntax is supported in Cosmos DB when defining composite indexes?
Cosmos DB supports /* as wildcards in JSON path definitions when defining composite indexes.
Is it necessary to index every attribute of the document in Cosmos DB?
No, it is not necessary to index every attribute of the document in Cosmos DB. You can choose to include or exclude certain attributes from indexing, based on the needs of your application.
How are the index entries for the composite indexes stored in Cosmos DB?
In Cosmos DB, the index entries for the composite indexes are stored in lexicographical order of the property values.
Can you use composite indexes with the SQL API in Cosmos DB?
Yes, you can use composite indexes with the SQL API in Cosmos DB to improve the performance of queries that use ORDER BY clauses.
What is the syntax to define composite indexes in Cosmos DB using Azure portal?
To define composite indexes in Cosmos DB using Azure portal, you need to provide the path and the order in the ‘Composite Indexes’ section of the ‘Indexing Policy’ tab.
Does the order of paths in a composite index matter in Cosmos DB?
Yes, the order of paths in a composite index does matter in Cosmos DB. The sort order (ascending or descending) of each path determines how the data is indexed and queried.
Can composite indexes in Cosmos DB be used with array elements?
Yes, composite indexes in Cosmos DB can be used with array elements. However, it requires a careful understanding of how the array elements will be indexed.
What are the two types of indexing policies in Cosmos DB?
The two types of indexing policies in Cosmos DB are strict and lazy. Strict indexing policy means that every write operation will first write to the index, while with a lazy indexing policy, write operations do not depend on index updating.
What is the impact of composite indexing on the Request Unit (RU) consumption in Cosmos DB?
Implementing composite indexes can have a significant impact on Request Unit (RU) consumption in Cosmos DB. Depending on the size and complexity of the composite index, it can increase or decrease the RU consumption of write and query operations.
What happens if the properties specified in the composite index do not exist in some documents in Cosmos DB?
If the properties specified in the composite index do not exist in some documents, Cosmos DB will create placeholder values in the index for the missing properties. This ensures that every document can be looked up using the composite index.
extutorials.com