Cosmos db 1RU point read latency never below 20 ms

Question

Hi,

so we have several asp net core apis .7 or 8 (app services) where we are seeing average latencies for 1 RU point reads are between 20-25 ms on average in the last 30 days. The lowest registered was 10 ms.
Looking at the SLA we should almost never see this.

We have located the cosmos account in the same region as the app service and we are using direct connection.
The cosmos hosting is serverless (but that should not matter according to the SLA), and the app service plan is P1mv3. The requests vary from less than 1/s to 3/s.

Any thoughts on what we could be missing?

Answer 1

Hi @erik eriksson

Thanks for the question and using MS Q&A platform.

It appears that you are experiencing higher-than-expected latencies for 1 RU point reads in your Azure Cosmos DB setup. Considering that your app services and Cosmos DB are in the same region and you are using direct connection mode, there are several factors that could explain this behavior and steps you can take to diagnose or mitigate the issue:

Request throttling is the most common reason for slow requests. Azure Cosmos DB throttles requests if they exceed the allocated request units for the database or container. The SDK has built-in logic to retry these requests. The request rate too large troubleshooting article explains how to check if the requests are being throttled. The article also discusses how to scale your account to avoid these problems in the future.

If the workload varies, even with a low rate (1-3 requests per second), the serverless tier might occasionally experience delays due to unexpected concurrent loads. This could explain the latency spikes you are observing, particularly if Cosmos DB needs to dynamically scale to handle more requests.

Please go through this documentation that might help you: Application design

https://learn.microsoft.com/en-us/azure/cosmos-db/monitor-server-side-latency
https://learn.microsoft.com/en-us/azure/cosmos-db/nosql/performance-tips-query-sdk?tabs=v3&pivots=programming-language-csharp

https://learn.microsoft.com/en-us/azure/cosmos-db/nosql/troubleshoot-dotnet-sdk-slow-request?tabs=cpu-new

please refer to this similar thread: https://learn.microsoft.com/en-us/answers/questions/2115745/how-to-fix-cosmos-db-latency-in-non-primary-region.

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