Time to Live (TTL) is a handy property that you can set for your documents in Azure Cosmos DB. This property automatically removes the documents from your container after a specified period. This way, you can easily manage the lifecycle of data that isn’t required to be stored indefinitely.
Setting a document’s TTL enables you to define the duration in seconds after which Azure Cosmos DB can automatically delete the document from the database. The TTL clock starts ticking at the point of the document’s creation and is based on the system’s clock rather than the local machine’s clock.
One of the primary uses of TTL is to remove transient data or data no longer relevant after a certain period of time. This method is both resource-friendly and cost-effective, as it reduces the storage and provisioned throughput necessary for manual delete operations.
Documents can have an individual TTL value, or a default TTL value can be set at the container level. Note that if both values are set, the document’s TTL will take precedence.
How to Set TTL in Azure Cosmos DB
To get started with setting the TTL in Azure Cosmos DB, follow these steps:
- Specify the TTL on a document: For individual documents, the TTL can be set by including an attribute “_ts” with the number of seconds after which the document should expire.
Here’s an example:
{
“id”: “123”,
“name”: “example”,
“_ts”: 3600
}
Here, ‘_ts’ value 3600 means that the document will expire an hour after its creation or last update.
- Specify the default container-level TTL: You can set a default TTL for all the documents in a container during its creation or modify it later. Here’s how to do this:
In the Azure portal, navigate to your Cosmos DB account, then to the ‘Containers’ panel. For an existing container, click on the ‘…’ button, then ‘Scale & Settings’. You can find the ‘Default Time to Live’ section here.
Remember that setting the TTL at the container level won’t affect the existing documents unless you update them and apply the TTL manually.
- Disable TTL: If you want to disable the TTL functionality, set the ‘Default Time to Live’ to null in the container settings or set the TTL property in the document to -1.
Conclusion
In conclusion, TTL is an effective tool in managing the lifecycle of documents in Azure Cosmos DB. By allowing automatic deletion of data, it helps save resources that would have been allocated for manual delete operations, simplifying the process of data handling in your application. Before implementing it, ensure that your application design considers the impact of automatic data removal.
Practice Test
True or False: In Azure Cosmos DB, you can set TTL (Time To Live) for a specific document.
- True
- False
Answer: True
Explanation: Azure Cosmos DB allows you to set TTL at both the container and individual document levels, providing flexibility depending on your requirements.
What does TTL (Time To Live) in Azure Cosmos DB refer to?
- A) The time taken for a data packet to reach its destination
- B) The duration, in seconds, that a document is retained in the Azure Cosmos DB
- C) The processing time of a document in Azure Cosmos DB
Answer: B) The duration, in seconds, that a document is retained in the Azure Cosmos DB
Explanation: TTL is the period, in seconds, a document should exist before it is automatically deleted from the database.
True or False: When you specify TTL at the document level in Azure Cosmos DB, it will override the TTL specified at the container level.
- True
- False
Answer: True
Explanation: When TTL is set at the document level, it takes precedence over the TTL set at the container level for that particular document.
True or False: The default setting for TTL in Azure Cosmos DB is to never expire.
- True
- False
Answer: True
Explanation: If no TTL is specified, the default is -1, which means the document does not expire.
What are ways to set TTL for a document in Azure Cosmos DB?
- A) Using the Azure Cosmos DB .NET SDK
- B) Using the Azure portal
- C) Both A and B
Answer: C) Both A and B
Explanation: TTL for a document can be set both programmatically, using the Azure Cosmos DB .NET SDK, and manually, using the Azure portal.
True or False: When a document’s TTL expires, it is deleted immediately from Azure Cosmos DB.
- True
- False
Answer: False
Explanation: Once a document’s TTL has expired, Azure Cosmos DB service will automatically remove it, but the deletion is not immediate and can be delayed due to service workload.
When TTL is set to null for a document in Azure Cosmos DB, what does it imply?
- A) The document is deleted immediately
- B) The document’s TTL follows the default TTL at the container level
- C) Both A and B
Answer: B) The document’s TTL follows the default TTL at the container level
Explanation: When TTL is set to null or removed from a document’s metadata, the document inherits the default TTL of the container.
True or False: TTL in Azure Cosmos DB does not consume any RU/s (Request Unit per second) for delete operations.
- True
- False
Answer: True
Explanation: Azure Cosmos DB’s TTL feature does not consume any RU/s for delete operations, making it a cost-effective way to remove expired data.
Single Select: What is the minimum TTL value that you can set for a document in Azure Cosmos DB?
- A) 0 seconds
- B) 1 second
- C) -1 second
Answer: B) 1 second
Explanation: The TTL can be set to any positive integer, with the minimum value being 1 second. If TTL is set to -1, the document will never expire.
True or False: Enabling TTL on a container in Azure Cosmos DB will automatically delete all the existing documents after the specified TTL value.
- True
- False
Answer: False
Explanation: When TTL is enabled on a container level, it does not affect the existing documents unless their TTL value is null. When document’s TTL is null, they inherit the container’s TTL value.
Multiple Select: Enabling TTL in Azure Cosmos DB helps to:
- A) Automatically delete old documents
- B) Conserve storage space
- C) Lower the cost
- D) All of the above
Answer: D) All of the above
Explanation: By managing the lifecycle of the documents and removing them after a certain period, Azure Cosmos DB not only helps in automatically deleting old and not needed documents but also saving storage cost.
True or False: You can specify TTL for a document while creating or updating it.
- True
- False
Answer: True
Explanation: The TTL for a document can be specified or updated during the creation or update process respectively.
Multiple Select: At which of the following levels can TTL be set in Azure Cosmos DB.
- A) Database level
- B) Cluster level
- C) Document level
- D) Container Level
Answer: C) Document level and D) Container Level
Explanation: In Azure Cosmos DB, TTL can be set at two levels: the container level and the document level.
True or False: It is mandatory to set TTL for documents in Azure Cosmos DB.
- True
- False
Answer: False
Explanation: Setting TTL for documents in Azure Cosmos DB is optional, providing added flexibility depending on use-case requirements.
If TTL is not set at the document level, the document’s lifespan will depend on:
- A) The size of the document
- B) The default TTL of the container
- C) The number of requests to the document
- D) None of the above
Answer: B) The default TTL of the container
Explanation: If TTL is not set at the document level in Azure Cosmos DB, the document’s lifespan will depend on the TTL set at the container level.
Interview Questions
What does TTL stand for in the context of Cosmos DB?
TTL stands for Time to Live. It’s a setting that determines how long documents should be kept before they are automatically deleted.
How do you enable TTL on a document in Azure Cosmos DB?
You can enable TTL on a document in Azure Cosmos DB by setting the ‘ttl’ value to a specific number of seconds after which the document should expire.
What is the default setting for TTL in Azure Cosmos DB?
The default setting for TTL in Azure Cosmos DB is ‘null’, which means the document will never expire.
Is it possible to specify a different TTL for each document within a collection in Azure Cosmos DB?
Yes, it is possible to specify a different TTL for each document within a collection. This is done by including a ‘ttl’ attribute in the document’s metadata.
Can you change the TTL of a document after it has been created in Azure Cosmos DB?
Yes, you can change the TTL of a document after it has been created. You can do this by updating the ‘ttl’ attribute in the document’s metadata.
What is the smallest value that can be set for TTL in Azure Cosmos DB?
The smallest value that can be set for TTL is one second.
How does Azure Cosmos DB handle documents when their TTL has expired?
When documents’ TTL has expired, Azure Cosmos DB automatically removes these documents to reduce storage consumption and cost.
Is there any cost associated with the automatic deletion of documents once their TTL expires in Azure Cosmos DB?
No, there is no cost associated with the automatic deletion of documents once their TTL expires.
In what unit should the TTL value be specified in Azure Cosmos DB?
The TTL value in Azure Cosmos DB should be specified in seconds.
Can you disable TTL for a document after it has been enabled in Azure Cosmos DB?
Yes, you can disable TTL for a document by setting the ‘ttl’ value to ‘null’ or by removing the ‘ttl’ attribute from the document’s metadata.
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