Skip to main content

Azure CosmosDB Request Unit considerations

So I have been doing a deep dive into Azure CosmosDB for a project. One of my objectives was to learn its performance characteristics when uploading a few million records an hour, and doing a cost analysis of CosmosDB vs other technologies already in use.  I put together an app that's able to push a few hundred records in at an acceptable rate.  So I do what I inevitably always do. From my laptop on hotel internet, I "dial it up to 11, and see what brakes", what could go wrong?

Well, it worked, and as expected, throttled when it hit the RU (Request Unit) limit.  I increased the RU allocation, and it pushed more documents per second.  Cool? NO, I was pushing 10,000+ RU/s and only getting a few hundred documents a second.  So I did what I should have done to start with, ran the sample from a VM in the same datacenter as my DB.  BINGO, it easily surpassed 1,000 documents per second. But for the same RU/s?

What's going on? Well after a bit of testing, I suspect that the RU calculation is primarily, if not exclusively, a function of time between when you open that socket and you get the "200 OK" back.  That includes how long it takes you to send the data.  Meaning that 10 MBs of documents sent at 1MB/s will be many times more expensive than the same documents sent at 1GB/s.

TL;DR : CosmosDB Request units are highly susceptible to connection latency.  So under load, even the latency between an Azure data center in Europe and the US will increase your RU/s used by a small amount.

So what do we do about this?  It's another factor you need to consider when selecting your replica data centers.  And you may get more than just lower latency on writes when using a "follow the sun" strategy with your master node.
Labels:

Popular posts from this blog

Service to service auth via Azure Active Directory

One of the things I like with the newer services from Azure is the use of Azure AD to authenticate. Azure Keyvault is a perfect example, I can request a JWT from Azure AD and I just pass that to Keyvault in the Authentication header and I am in. Bringing me back to the good old days when we would use Windows AD user as service accounts, you change your password in one place and it's updated everywhere. But this time, you can have more than one password, so your services don't crash as you try to cycle the passwords. (I think I hear angels singing from heaven...) So, how do we make use of this for our own services? So glad you asked. Let's start by pointing you to Microsoft's documentation for  Authentication Scenarios for Azure AD , it's a very good read, and you really should know this stuff before starting this.  The scenario we are looking for is "Daemon or Server Application to Web API", particularly looking at how Web APP 1 ( TodoListDaemon ) and ...
Read more

Querying for items in an Array in CosmosDB

If you have spent any time looking at the documentation for Microsoft CosmosDB / DocumentDB, you will see a lot of examples where the data model has a property named "Tags" that is a list of strings.  But you don't see many times they query on something in that Tag property...  One example I saw a query on Tags[0] = "some value" I don't know how often I will need that, but you know, good to know you can do it. After looking through the SQL syntax reference .  The 2 ways I most likely query the Tags would be to use a join on the Tags property or use the ARRAY_CONTAINS function. Side note; the performance of the two methods are basically identical, leading me to believe the query optimizer generates the same instruction sets for both. So unless you have an array of complex objects, just use ARRAY_CONTAINS. Cool, we know how to query for documents that have our tag on them now... One small problem, when you load a million, or even a hundred thousand do...
Read more

Service to service auth via Azure Active Directory with ASP.Net Core

Sample configuration for ASP.Net Core 1.1 to use Azure AD for Service to Service Authentication.  Update your Startup.cs to have the following public void ConfigureServices(IServiceCollection services) { services.AddAuthentication(); ... } public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory) { app.UseJwtBearerAuthentication(new JwtBearerOptions { Authority = "https://login.microsoftonline.com/{AAD Tenant Name or ID}", Audience = "{Application ID URL}" }); ... } Microsoft.AspNetCore.Authentication.JwtBearer defaults to using OpenID Connect discovery document to validate the bearer token. The Authority is the prefix for the the discovery document.  The middleware will append ".well-known/openid-configuration/" to whatever you pass in to the Authority.  If your IDP has a diffrent endpoint for the discovery document, you can specify the MetadataAddress option, tha...
Read more