As the world shifts towards digital transformation, data management has never been more crucial. One of the most important aspects of data management is to ensure that it is always updated accurately. In this article, we delve into how to implement an update operation using a patch in the context of Azure Cosmos DB.
Azure Cosmos DB is a global, multi-model, distributed database service provided by Microsoft Azure that enables you to read and write data irrespective of where you are located, guarantees latency, and elastic scalability. It provides five different APIs – SQL(core), MongoDB, Table, Cassandra, and Gremlin, allows customers to build and deploy applications in a short span of time, and supports various data models, including documents, graphs, column families, and key-value pairs.
Understanding the Update Operation
Before reviewing the details of the patch operation, it is important to understand a little about the update operation. Typically, an update operation in Azure Cosmos DB involves reading the existing item, making modifications to it, and then replacing the older item with the new one. However, this consumes a considerable amount of RUs(Request Units) and makes transactions slower.
Optimizing operations with PATCH
For more optimized and efficient operations in Azure Cosmos DB, Microsoft allows using a partial document update, or PATCH operation. The PATCH operation updates an item by only modifying parts that need to be changed. It not only reduces the cost of operations but also increases performance for high-scale applications by saving network overhead and reducing I/O in Cosmos DB.
To perform a PATCH operation, the “x-ms-documentdb-IsUpsert” header must be set to “true.” Here, resources are updated only if they share the same “id,” otherwise, a new resource gets created. Some of the operations supported by PATCH include adding a new value, replacing an existing value, incrementing a numeric value, setting or removing an array element, and removing an existing value.
Remember, PATCH operations cannot be used with the SQL (core) API as full replacements are required.
Benefits of Using PATCH Operation
| Regular Update operation | PATCH operation | |
|---|---|---|
| RUs consumption | High | Low |
| Network Overhead | High | Low |
| Performance | Moderate | High |
| I/O in Cosmos DB | High | Low |
Sample PATCH Request
// Update an item by specifying a point update
ItemResponse<dynamic> patchResponse = await container.PatchItemAsync<dynamic>(
id: “id_here”,
partitionKey: new PartitionKey(“partition_key_here”),
patchOperations: new[]
{
PatchOperation.Replace(“/LastName”, “Smith”)
});
Console.WriteLine($”Updated item lastname to ‘Smith’. Operation consumed {patchResponse.RequestCharge} RUs.”);
So, when preparing for your DP-420 exam – Designing and Implementing Native Applications Using Microsoft Azure Cosmos DB, remember the PATCH operation presents an efficient and economical way to update, particularly vital for applications with high data throughput. Understanding the implementation and benefits of PATCH will help not just in the Azure Cosmos DB exam, but also beneficial in real-world applications using Azure Cosmos DB.
Practice Test
True or False: Azure Cosmos DB supports the PATCH method for partial updates to items.
- Answer: True
Explanation: Azure Cosmos DB supports the PATCH method, which can be used for partial updates on JSON items stored inside your containers. This allows for enhanced performance and reducing RU charges.
Which of the following Azure Cosmos DB APIs support PATCH operations?
- a) SQL API
- b) MongoDB API
- c) Cassandra API
- d) Gremlin API
- Answer: a) SQL API, b) MongoDB API
Explanation: As of now, PATCH operations are supported only in Azure Cosmos DB’s SQL and MongoDB APIs. Other APIs do not currently support PATCH operations.
True or False: Azure Cosmos DB does not support conditional patch operations.
- Answer: False
Explanation: Azure Cosmos DB provides support for conditional patch operations. You can perform a patch operation only when the specified condition is true.
When you utilize a PATCH operation in Azure Cosmos DB___
- a) The entire item is replaced
- b) Only specified attributes are updated
- c) The item is deleted and then reinserted
- d) None of the above
- Answer: b) Only specified attributes are updated
Explanation: A PATCH operation allows for selective updates of attributes within an item in Azure Cosmos DB, as opposed to replacing an entire item.
Which of the following can be used to locate an item for a PATCH operation in Azure Cosmos DB?
- a) id
- b) partition key
- c) object GUID
- d) both a) and b)
- Answer: d) both a) and b)
Explanation: To perform a patch operation, Azure Cosmos DB requires the id and partition key of the item. An object GUID cannot locate an item.
True or False: You can use the Azure Cosmos DB’s REST API to perform PATCH operations.
- Answer: True
Explanation: Azure Cosmos DB’s REST API allows you to perform PATCH operations, giving a way to update an item partially via REST commands.
In Azure Cosmos DB, a patch operation against a non-existing item will result in:
- a) Item creation
- b) A successful operation but no changes
- c) An error
- d) None of the above
- Answer: c) An error
Explanation: When executing a patch operation against a non-existing item in Azure Cosmos DB, an error will be returned.
True or False: PATCH operations are always transactional in Azure Cosmos DB.
- Answer: False
Explanation: Although Azure Cosmos DB supports transactional operations, a PATCH operation is not always transactional. It depends on the consistency level settings and the scope of the operation.
Which consistency model Azure Cosmos DB uses by default?
- a) Eventual consistency
- b) Strong consistency
- c) Bounded staleness
- d) Session consistency
- Answer: d) Session consistency
Explanation: By default, Azure Cosmos DB uses session consistency, which guarantees linearizability within a single session.
A Patch operation can be performed in Azure Cosmos DB using:
- a) Azure portal
- b) Azure CLI
- c) SDKs
- d) All of the above
- Answer: d) All of the above
Explanation: Azure Cosmos DB supports patch operations via the Azure portal, Azure CLI, and various SDKs. It makes database operations flexible and easier.
Interview Questions
What does a patch operation do in Azure Cosmos DB?
A patch operation in Azure Cosmos DB allows for selective update of a document’s properties without the requirement to download or read the document, modify the properties, and then substitute it. It makes the updating process more efficient.
How do you perform partial updates to Azure Cosmos DB items using the .NET SDK?
To perform partial updates to Azure Cosmos DB items, PatchAsync method is used in the .NET SDK.
Which HTTP verb is used by a PATCH operation in Azure Cosmos DB?
HTTP verb PATCH is employed for the partial update operation in Azure Cosmos DB.
Is there any difference between the PUT operation and the PATCH operation in Azure Cosmos DB?
Yes, there’s a considerable difference. PUT operation completely replaces an existing item with a new item, while the PATCH operation only updates selective properties of the existing item.
Can you patch documents that don’t contain the field you’re trying to update in Cosmos DB?
Yes, you can. A PATCH operation creates the target field when it doesn’t already exist.
What happens if you try to use a PATCH operation on a non-existent document in Azure Cosmos DB?
If you try to execute a PATCH operation on a non-existent document in Azure Cosmos DB, it will create a new document with the specified id and corresponding properties.
What does the term ‘patch payload’ mean in the context of Azure Cosmos DB?
In the context of Azure Cosmos DB, patch payload refers to the request body in a PATCH operation which specifies the changes to be applied to the target item.
What is the use of conditional access check in Azure Cosmos DB patch request?
Conditional access check in patch request ensures the application of update based on control access. It can prevent updates against stale content when used.
Can Azure Cosmos DB use a JSONPatch syntax to implement the PATCH operation?
Yes, Azure Cosmos DB can use JSONPatch operations syntax which include add, replace, remove, etc. operations.
Is patching operation in Azure Cosmos DB atomic?
Yes, patching operations in Azure Cosmos DB are atomic per partition key, which means all the operations specified in a single patch request will either all succeed or all fail.
What happens if a patch operation executed with Azure Cosmos DB fails?
If a patch operation executed with Azure Cosmos DB fails, none of the updates specified in the patch request are applied.
Can patch operations be used within a transactional batch in Azure Cosmos DB?
Yes, patch operations can be used within a transactional batch in Azure Cosmos DB.
What are the status codes for successful and unsuccessful patch operations in Azure Cosmos DB?
The status code for a successful patch operation in Azure Cosmos DB is ‘200 OK’ and for an unsuccessful patch operation, it is ‘412 Precondition Failed’.
How does ‘RetryAfterMilliseconds’ work in Cosmos DB patch operation?
In the event of a rate-limiting error, Cosmos DB client retries the request after the duration specified in RetryAfterMilliseconds.
Is a particular throughput consumed for rename and remove operations in Cosmos DB patching?
Yes, there is a particular RUs charge for rename and remove operations, same ways as the replace operation in Cosmos DB patching.
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