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Alfonso Subiotto

@asubiotto.com
88 followers 145 following 49 posts

Engineering at polarsignals.com & investing in devtools/data/infra at lorimerventures.com | Previously tech lead at cockroachlabs.com

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Alfonso Subiotto @asubiotto.com · 18/08/2026
@polarsignals.com is joining @dash0.com! We'll be integrating continuous profiling into Dash0 and replacing ClickHouse with Great Lakes, the storage engine we built to power Polar Signals. www.polarsignals.com/blog/posts/2...
polarsignals.com
Polar Signals is Joining Dash0 | Polar Signals
The next chapter for continuous profiling, our database, and the team
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Alfonso Subiotto @asubiotto.com · 24/06/2026
This was a fun one! For @polarsignals.com's latest hackathon, I wrote an FSST decompression CUDA kernel and then optimized it by profiling with our new GPU PC sampling feature. www.polarsignals.com/blog/posts/2...
polarsignals.com
My Journey Optimizing a CUDA Kernel with Polar Signals | Polar Signals
A storage engineer's descent into warp stalls, memory throttles, and aligned stores
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Alfonso Subiotto @asubiotto.com · 10/06/2026
If you're doing any performance work on GPUs, this is huge. PC sampling is a powerful tool for GPU optimization, but causes serial kernel executions. We've released production-ready continuous PC sampling so you can get GPU performance insights on your production workloads.
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Polar Signals @polarsignals.com · 20/05/2026
New Blog Alert! Learn how we overcame eBPF limits to unwind deeply nested PyTorch training stacks and learned some cools things along the way: www.polarsignals.com/blog/posts/2...
polarsignals.com
Python Zebra Stacks | Polar Signals
Unwinding Deep PyTorch Training Stacks with eBPF
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Polar Signals @polarsignals.com · 06/05/2026
🤖Using Polar Signals Cloud and Claude Code to autonomously optimize your code every day! 📈 Also: Check out our new website! What do you think? www.polarsignals.com/blog/posts/2...
polarsignals.com
Autonomous Optimization with Claude Code | Polar Signals
Optimize your infrastructure autonomously every day with Claude Code and Polar Signals
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Alfonso Subiotto @asubiotto.com · 28/04/2026
We just enabled the read path for all customers, and will be writing more about this soon! In the meantime, enjoy.
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Alfonso Subiotto @asubiotto.com · 28/04/2026
We've been working on a major schema migration at @polarsignals.com that has unlocked some pretty wild improvements. Apart from a 50% (!!) reduction in storage size thanks to logical compression in vortex.dev, there has been a dramatic improvement in query performance.
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Polar Signals @polarsignals.com · 15/04/2026
Tired of Node.js flamecharts full of `a`, `m`, and `_0x3f2`? We just shipped source maps support for Node.js profiles in Polar Signals Cloud. Just add a plugin to your build pipeline, and your profiles show the real code. Know more: www.polarsignals.com/blog/posts/2...
polarsignals.com
Do more with less. | Polar Signals
Polar Signals Cloud is an always-on, zero-instrumentation continuous profiling for CPU, GPU, and Memory that helps improve performance, understand incidents, and lower infrastructure costs.
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Alfonso Subiotto @asubiotto.com · 17/02/2026
I'm happy to share that I will be speaking at #QConLondon on March 16 on deterministic simulation testing at Polar Signals. For anyone interested in attending: SPEAKER60QUK26 for £60 off
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Alfonso Subiotto @asubiotto.com · 14/01/2026
Claude is down. I guess I have to learn how to code again.
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Polar Signals @polarsignals.com · 08/01/2026
📢 It’s a new year so we’re announcing something new which is the Sandwich view: A way to visualize a function’s callers and callees side by side for better debugging and performance work. Read more about it here: www.polarsignals.com/blog/posts/2...
polarsignals.com
Introducing the Sandwich View
A new way to visualize a function’s callers and callees side by side.
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Alfonso Subiotto @asubiotto.com · 07/01/2026
My EuroRust talk has been uploaded to YT! I cover how we architected our Rust database at @polarsignals.com as a set of state machines to enable deterministic simulation testing and catch hard-to-reproduce bugs before they hit prod.
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Alfonso Subiotto @asubiotto.com · 23/12/2025
Absolutely! I can't imagine going back to not having continuous system-wide profiling 🙈
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Alfonso Subiotto @asubiotto.com · 23/12/2025
A simple 50-line code change saves us 30% of CPU across our whole infrastructure. This is the magic of system-wide profiling with @polarsignals.com. Easy to spot, easy to fix.
github.com
performance[vortex-array]: don't call is_valid to count bytes in varbinview by asubiotto · Pull Request #5814 · vortex-data/vortex
I noticed that the better blocks compressor uses count_referenced_bytes which calls is_valid on each view and results in an expensive scalar_at call. This was 30% of our system-wide CPU usage over ...
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Polar Signals @polarsignals.com · 18/12/2025
🚀 We recently announced our NVIDIA CUDA always-on profiler. Check out this blog on how to try it out super quickly with your CUDA workload today!🧊 www.polarsignals.com/blog/posts/2...
polarsignals.com
Profiling NVIDIA CUDA in Kubernetes
The easiest way to get started Profiling CUDA in Kubernetes
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Alfonso Subiotto @asubiotto.com · 15/12/2025
Happy to share that I've been nominated to the Vortex Technical Steering Committee! It's been fun and productive switching to Vortex from Parquet as our storage format @polarsignals.com and I'm excited to continue contributing to the Vortex project. vortex.dev/blog/novembe...
vortex.dev
November Bulletin | Vortex Blog
Overview of all work happening in Vortex
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Polar Signals @polarsignals.com · 04/12/2025
🧊 New on the Polar Signals Blog — Our Delta Lake Fork Purpose-built for our continuous profiling product. In our latest post, we walk through how Delta Lake works, and the changes we've made to improve performance for our product. 👉 Read the full post: buff.ly/KwHINtO
polarsignals.com
Great Lakes: A Delta Lake Fork
Our updates to Delta Lake Table Format
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Alfonso Subiotto @asubiotto.com · 25/11/2025
www.polarsignals.com/blog/posts/2...
polarsignals.com
Do more with less. | Polar Signals
Polar Signals Cloud is an always-on, zero-instrumentation continuous profiling for CPU, GPU, and Memory that helps improve performance, understand incidents, and lower infrastructure costs.
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Alfonso Subiotto @asubiotto.com · 25/11/2025
Sometimes an interface is so ubiquitous that performance limitations inherent to its design are just accepted. This has been our experience with Parquet. We switched to Vortex which aligned much better with our needs and saw a 70% performance improvement across the board. Read more below 👇
polarsignals.com
Do more with less. | Polar Signals
Polar Signals Cloud is an always-on, zero-instrumentation continuous profiling for CPU, GPU, and Memory that helps improve performance, understand incidents, and lower infrastructure costs.
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Polar Signals @polarsignals.com · 04/11/2025
Ever wondered how your browser devtools jumps from bundle.min.js:1:27698 → src/index.ts:73:16? 🧊 We unpack the internals of JS Source Maps: Base64 VLQ encoding, mapping deltas, and how your original TS code gets reconstructed from minified bundles. 🔗 www.polarsignals.com/blog/posts/2...
polarsignals.com
The Inner Workings of JavaScript Source Maps
A deep dive into how JavaScript source maps work under the hood, with examples showing how all the pieces fit together.
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Alfonso Subiotto @asubiotto.com · 22/10/2025
Introducing the world's first open source continuous NVIDIA CUDA profiler. Zero code changes required, low overhead, and always on.
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aksh1618 @aksh1618.aksh.dev · 10/10/2025
Took advantage of the lunch break to replay this great talk by Alfonso Subiotto (@asubiotto.com) making the case for a State Machines based approach to Deterministic Simulation Testing, being used at @polarsignals.com, very interesting! Their inspiration for this: sled.rs/simulation
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Polar Signals @polarsignals.com · 03/09/2025
We're excited to be at @rustconf.com 2025! Let's talk about profiling Rust with zero compromise! #rustconf25
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Polar Signals @polarsignals.com · 03/09/2025
We recently made some performance improvements to our Flame Graph by implementing backend pre-computation and viewport culling. Read more in our latest blog post: www.polarsignals.com/blog/posts/2...
polarsignals.com
Parallel Flame Graph Rendering
How we improved our flame graph rendering by moving computation to the backend.
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Alfonso Subiotto @asubiotto.com · 26/08/2025
I wrote about why we should treat German string encoding/StringViews as Just Another Encoding™
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Alfonso Subiotto @asubiotto.com · 22/08/2025
Thanks for the pointer. Do you know where though? This is what I could find of the representation: github.com/vortex-data/.... Also the pushed-down filter kernel seems to convert to arrow and delegate: github.com/vortex-data/.... In arrow I'm pretty sure the prefixes are not a separate array.
github.com
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Alfonso Subiotto @asubiotto.com · 20/08/2025
Do any database systems "columnarize" the German string encoding so rather than storing a 16-byte view for each element which includes length+prefix+pointer you'd store all lengths together, prefixes together etc...? Seems like prefix operations would be more SIMD friendly.
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Alfonso Subiotto @asubiotto.com · 19/08/2025
The hardest part about writing a blog post is the introduction. Here I am, 4 hours later.
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Polar Signals @polarsignals.com · 13/08/2025
Tame the OOM killer with OOMProf, the new eBPF memory profiler for Go programs being taken out by the kernels OOM killer! www.polarsignals.com/blog/posts/2...
polarsignals.com
OOMProf - Profiling on the Brink
Using eBPF to record your programs dying breathes
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Polar Signals @polarsignals.com · 07/08/2025
We're excited to share that the Parca Agent now works offline! Store CPU profiles locally when disconnected, upload when ready. Because not all computing happens in data centers. Read how we built it: www.polarsignals.com/blog/posts/2...
polarsignals.com
Offline Mode for the Parca Agent
Collect and upload profiles -- even without a network connection
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Alfonso Subiotto @asubiotto.com · 31/07/2025
Problem: Everything is JSON. Solution: MORE JSON! Haha, but thanks for pointing this out. Now I'm going to have to do a little researching
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Alfonso Subiotto @asubiotto.com · 31/07/2025
New storage format RFC in the works 👀 Early preview:
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Polar Signals @polarsignals.com · 30/07/2025
🚀 Today, we're excited to launch Off-CPU profiling! Check out our blog on what we needed to do to make it most useful and how you can get started with it! 🧊 www.polarsignals.com/blog/posts/2...
polarsignals.com
Introducing Off-CPU Profiling
How Off-CPU profiling works and how to get the most out of it
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Alfonso Subiotto @asubiotto.com · 29/07/2025
Unfortunately no plans to be in SF around then but we'll keep it in mind in case anyone does end up being there.
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Alfonso Subiotto @asubiotto.com · 18/07/2025
@metalmatze.de built an MCP server so you can hook up your agent to your profiling data. Check it out!
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Polar Signals @polarsignals.com · 08/07/2025
📔Writing our Rust database from scratch gave us a golden opportunity to implement deterministic simulation testing as a core feature. Learn about the architecture that gives us full control over DST ingredients. 🧊 www.polarsignals.com/blog/posts/2...
polarsignals.com
Deterministic Simulation Testing in Rust: A Theater Of State Machines
How we designed our database for complete control over concurrency, time, randomness, and failure injection.
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Alfonso Subiotto @asubiotto.com · 08/07/2025
I assumed links were downranked everywhere, good to know!
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Alfonso Subiotto @asubiotto.com · 08/07/2025
www.polarsignals.com/blog/posts/2...
polarsignals.com
Deterministic Simulation Testing in Rust: A Theater Of State Machines
How we designed our database for complete control over concurrency, time, randomness, and failure injection.
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Alfonso Subiotto @asubiotto.com · 08/07/2025
Writing our Rust database from scratch gave us a golden opportunity to implement deterministic simulation testing as a core feature. I wrote a blog post about the architecture that gives us full control over concurrency, time, randomness, and failure injection. (link in comment)
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Alfonso Subiotto @asubiotto.com · 07/07/2025
If you're serious about performance, you need continuous profiling in your life
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Alfonso Subiotto @asubiotto.com · 07/07/2025
Nice read about how maybe it's time to delete some tests (not your DST test though): andre.arko.net/2025/06/30/y...
andre.arko.net
You should delete tests
We’ve had decades of thought leadership around testing, especially coming from wholistic development philosophies like Agile, TDD, and BDD. After all that time and several supposedly superseding…
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Chris @chris.blue · 04/07/2025
This was a fun read. Speed runs building a cloud DB. Hill climbing the design can lead to a local maximum. Lots of lessons. Now I need to read their next post on the new one!
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Alfonso Subiotto @asubiotto.com · 04/07/2025
Looking forward to speaking at @eurorust.eu about the deterministic simulation testing we're doing at @polarsignals.com!
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Frederic Branczyk @brancz.com · 20/06/2025
Our very own @asubiotto.bsky.social for the first time publicly talking about the DST approach we’re taking in our new database. (Blog post coming soon as well!)
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Alfonso Subiotto @asubiotto.com · 18/06/2025
www.polarsignals.com/blog/posts/2...
polarsignals.com
New year new database
Bringing what we've learned to our next generation database.
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Alfonso Subiotto @asubiotto.com · 18/06/2025
You know that urge to rewrite your database in Rust? We gave in. (Link in comment)
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Alfonso Subiotto @asubiotto.com · 18/06/2025
Off to Systems Distributed. See you in Amsterdam!
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Alfonso Subiotto @asubiotto.com · 12/06/2025
Quis verificabit ipsos verificatores?
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Alfonso Subiotto @asubiotto.com · 10/06/2025
Claude code seems to love debugging by pointing at random code paths it doesn't understand and saying "the root cause is now clear"
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Polar Signals @polarsignals.com · 04/06/2025
We've been working hard to enhance our continuous profiling for GPUs. Learn about more metrics (like PCIe throughput) and the upcoming On-GPU profiles. If you are attending ai.engineer, come and stop by our booth S18 to discuss all of these features! www.polarsignals.com/blog/posts/2...
polarsignals.com
Latest in Continuous Profiling for GPUs
Attending ai.engineer 2025 in San Francisco
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