ASP.NET Core–Performance tip

Question: What is wrong with the following ASP.NET Core controller:

No idea?

Take a look at the return type...

Returning IEnumerable from an action results in synchronous collection iteration by the serializer. The result is the blocking of calls and a potential for thread pool starvation.

One possible way to avoid this is by explicitly invoking ToListAsync before returning the result:

Starting from ASP.NET Core 3.0 you can also use IAsyncEnumerable<T>. This no longer results in synchronous iteration and is as efficient as returning IEnumerable<T>.

Let’s rewrite the example above to use IAsyncEnumerable<T>:

REMARK: If we take a look at the original example again, it will not be an issue in ASP.NET Core 3.0 or higher. Why? Because we allow the framework to choose how to handle the IQueryable<T> we get back from the Where() clause. In the situation we are using ASP.NET Core 3.0 or higher the results will be buffered and correctly provided to the serializer. However this is implicit behavior that doesn’t work in all situations(it depends on the underlying types used).

More information and other performance tips can be found here: https://docs.microsoft.com/en-us/aspnet/core/performance/performance-best-practices

Podman– Command execution failed with exit code 125

After updating WSL on one of the developer machines, Podman failed to work. When we took a look through Podman Desktop, we noticed that Podman had stopped running and returned the following error message: Error: Command execution failed with exit code 125 Here are the steps we tried to fix the issue: We started by running podman info to get some extra details on what could be wrong: >podman info OS: windows/amd64 provider: wsl version: 5.3.1 Cannot connect to Podman. Please verify your connection to the Linux system using `podman system connection list`, or try `podman machine init` and `podman machine start` to manage a new Linux VM Error: unable to connect to Podman socket: failed to connect: dial tcp 127.0.0.1:2655: connectex: No connection could be made because the target machine actively refused it. That makes sense as the podman VM was not running. Let’s check the VM: >podman machine list NAME ...

Cache stampede: when our cache turned against us

While investigating some performance issues, we ran into an ASP.NET Core API that cached a fairly expensive aggregation query for 60 seconds. Under normal load, that was fine: one request rebuilds the cache, everyone else reads from it. Under peak load, dozens of requests would arrive in that same expiry window, all see a cache miss, and all fire the same expensive query in parallel. The database didn't like that. That was the moment when our caching layer stopped helping and started hurting. A burst of requests comes in at the same time, all miss the cache, and all go hammer the database or the downstream API at once. That's a cache stampede . The cache was supposed to protect our backend, and for a few hundred milliseconds it did the opposite. Why this happens IMemoryCache.GetOrCreate (and its async sibling) looks like it protects you, but it doesn't add any locking on its own. Look at the naive version: public async Task<Report> GetReportAsync(string key) ...

Azure DevOps/ GitHub emoji

I’m really bad at remembering emoji’s. So here is cheat sheet with all emoji’s that can be used in tools that support the github emoji markdown markup: All credits go to rcaviers who created this list.

The art of simplicity

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