Felix Geisendörfer

Software Engineer @datadoghq working on Go Profiling, Performance, OpenTelemetry and more. Before: @Apple, Co-founder @transloadit, @nodejs core dev

[Felix Geisendörfer @felixge]

🚀 Would you like to improve the latency of your Go apps?

In the video below I'll walk you through 5 optimizations using @datadoghq's new profiling timeline feature. Finding and fixing those problems would have been really hard with other tools ✨.

https://t.co/RxO7snGbRe

[Felix Geisendörfer @felixge]

@mraleph No response, which is why I'm casting a wider net 🙈.

[Felix Geisendörfer @felixge]

If anybody with connections to the V8/Chrome team is reading this, my colleague Attila is trying to find a reviewer for a patch to improving profiling.

Many thanks in advance for any leads 🙇🏻‍♂️

https://t.co/wzrweU2P8L

[Felix Geisendörfer @felixge]

@trevorlasn I think we mostly care about throughput for these services. They auto-scale on CPU, so this translates into cost savings.

[Felix Geisendörfer @felixge]

PSA: Green Tea GC in go1.26 is incredible 🚀

This is what we saw for two big Go services.

We'll try to gather more data and share it soon.

[Felix Geisendörfer @felixge]

@NguyenD56197615 AFAIK the second service does some in-memory caching. It takes a while for the cache to fill up. During this time, heap size increases, and so does GC overhead b/c it's proportional to the number of live pointers on the heap.

[Felix Geisendörfer @felixge]

Commodification goes both ways. Sorry, I don't make the rules. 🤷🏻‍♂️

[Felix Geisendörfer @felixge]

I just published a proposal for a new RSS profile type for Go.

It aims to solve the issue that the heap profile typically shows < 50% of process RSS, which is very confusing.

It should also help to quickly identify when memory usage is dominated by cgo.

https://t.co/9IcvNZB50W

[Felix Geisendörfer @felixge]

In exchange for 18 minutes of your time, you can get an elevator pitch about why you should be using pi (instead of claude) and perhaps more importantly, one of the sanest takes on using AI effectively 🔥

https://t.co/6qnnkyftO9

[Felix Geisendörfer @felixge]

@richardartoul IIRC joyent did this in 2013. It struck me as a smart thing back then, but it seems like it hasn’t caught on … yet?

https://t.co/3GSlszaPn8

[Felix Geisendörfer @felixge]

@mav3ri3k @thorstenball Valid concern. But I've tackled this with a skill + CLAUDE.md entry and it works well for me.

https://t.co/YJ0VZvtUkc
https://t.co/X8RGKRrUjR

[Felix Geisendörfer @felixge]

And of course, if you're looking for a vendor, Datadog has you covered.

You can join the preview for the OpenTelemetry eBPF profiler here:

https://t.co/DSliaFVE2l

[Felix Geisendörfer @felixge]

The OpenTelemetry Profiles Signal is now in Alpha 🚀

This is a big step towards making Continuous Profiling in production available to the whole industry.

And given the rise of AI coding, this couldn't come at a better moment in time ... 🧵

[Felix Geisendörfer @felixge]

If this sounds interesting to you, and you'd like to get an early taste of the troubleshooting powers of the Profiles Signal, please check out our post on the OpenTelemetry blog for more details:

https://t.co/4dbhJmuuSc

[Felix Geisendörfer @felixge]

I’m headed to KubeCon Amsterdam where I’ll be talking about the otel profiling signal graduating to alpha stability.

HMU if you want to chat about otel, go, o11y, profiling or anything else. I’m in town until Thursday night.

[Felix Geisendörfer @felixge]

@iDeco_UK Hm, lazy-mcp looks interesting, but at 77 gh stars I'm unsure if I wouldn't be better off hacking my own version 😅.

[Felix Geisendörfer @felixge]

Why is configuring MCP servers for claude such a tire fire? Can't configure them in settings.json (only in ~/.claude.json). Can't have them disabled by default (only per project).

I guess it's good for business to treat them as an append-only token guzzling machine?

[Felix Geisendörfer @felixge]

@perrito666 Ack. Yeah, I can think of a few ways to hack my way around the problem.

I'm just astonished that this isn't a solved problem out of the box in 2026 ... 🤕

[Felix Geisendörfer @felixge]

If somebody has a good solution, e.g. some sort of mcp proxy that's not a PITA in its own right, LMK.

[Felix Geisendörfer @felixge]

And yes, I prefer CLI tools this days.

But for some tools I need at work there are no good CLI (e.g. confluence) options, and even when they exist (e.g. snowflake) they can run into funny issues like oauth sessions not being cached due to global policies.