Logs on Motiejus Jakštys Public Record

Scaling Btrfs in an Enterprise

Fri, 27 Mar 2026 13:54:15 +0000

This first been published in The New Stack: Scaling Btrfs to petabytes in production: a 74% cost reduction story. I am replicating a late draft of this post here for archival reasons.

We saved 74% of our storage costs by moving petabytes of time-series data from ext4 to Btrfs. We are partnering with Google to bring Btrfs to all GCP customers, you can experimentally run Btrfs on GCP today. Here is how we did that without blowing up production. This is an expanded blog post of a conference talk that aired in FOSDEM 2026.

Testing LiFePo4 15Ah with Gyrfalcon s8000

Sat, 03 Jan 2026 09:40:59 +0200

I recently went into a rabbit hole of finding the best battery pack for an electronic candle that will be installed in a large Christmas Wreath. The pair of alkaline batteries holds the charge for 2-3 days; my goal is 7 more. Ideally — 30. The light draws 39mAh:

Candle light draws 39mAh from a 3.2V power source

Construction site surveillance

Tue, 01 Apr 2025 14:26:00 +0200

I am building a house, for which I decided I need a surveilance cameras. I have never set up a security camera, so have zero knowledge before starting. Here are the prelminary requirements before I started:

24/7 on-demand live view, plus some recording: 7 days 24/7, plus some time for when and around “motion” is detected.
Nothing that has a subscription fee. ring.com is pretty good for short-term plug&play, but I cannot brace myself for a yearly payment, especially that I have (and can afford to maintain and upgrade) storage, network and compute. Network subscription is a fine service to pay for, SaaS is not.
Use off-the-shelf hardware, so I am only minimally required to maintain the setup (so no DYI webcams or routers).

This post highlights some things I wish I knew before buying & setting it all up.

Family Single Sign On Was a Bad Idea

Sat, 23 Nov 2024 21:41:39 +0200

When my eldest son became of an email-qualified age, I set him up a Bitwarden instance, so he can keep his password there. He loved it.

My password manager instance is not open to the public internet, necessitating use of VPN software, which needed a method to authenticate (a.k.a. login method).

As someone inundated into “best practice” security policies of a 10k+-engineer corporation for quite a while, I built my home authentication system using the only method I really respected: single-sign-on. I thought that having a single password for all of our services will be convenient and quite easy. So I set up SSO for a few services that my family uses, including the VPN software.

Zig Reproduced Without Binaries

Tue, 12 Nov 2024 22:21:48 +0200

I decided to bootstrap Zig without using binaries that are checked in the repository and answer if the resulting zig1.wasm in the latest Zig release (0.13.0) is the same the one bootstrapped without using those binaries.

TLDR: yes, they are the same:

$ sha256sum code/zig{,2}/stage1/zig1.wasm
127909fb8c9610ce3f296d8a48014546c0f85055115002fb3aba4d865dcdbb27  code/zig/stage1/zig1.wasm
127909fb8c9610ce3f296d8a48014546c0f85055115002fb3aba4d865dcdbb27  code/zig2/stage1/zig1.wasm

I can now confidently say (and you can also check, you don’t need to trust me) that there is nothing hiding in zig1.wasm that hasn’t been checked-in as a source file.

I have successfully re-googled myself

Wed, 09 Oct 2024 20:59:43 -0400

It is quite common across tech folk (at least the ones that I speak of) to “de-google”. I.e. get rid of Google (or, in general, big-corp) services. As you can imagine, after running, say, e-mail for 15+ years, the process (and the result) isn’t fun.

I got rid of my Gmail account in the Christmas of 2023, so about 10 months ago. The result was rewarding, but only because I felt “de-googled”. It took just a few weeks to realize that it is not the end of it.

Web Compression

Wed, 07 Aug 2024 13:53:10 +0300

I wrote this comment about pre-compressing web artifacts with zstd:

I have read somewhere (can’t find links handy) that for web server case, zstd may not be as useful as brotli due to longer decompression speed, but I may be wrong here.

That felt wrong — someone suggesting a cool change in a module, and I am just FUDing it. If I were the PR submitter, I would certainly not appreciate this comment. So I decided to conduct a non-scientific experiment: take a big piece of Javascript and compare brotli with zstd.

11sync shutdown

Mon, 01 Jul 2024 00:04:30 +0300

As you may have read, I have created a “hosted syncthing” pre-registration page in 11sync.net. The 1-sentence pitch for the service is:

11sync.net is a Hosted Syncthing peer. Designed for Syncthing users seeking reliable backups and resilience.

Over the ~6 months sign-up page was live, 46 people¹ signed up. This sign-up activity signals this will unlikely be a sustainable business, so I am halting all activity and will terminate the sign-up page soon. Thank you for your interest if you have signed up, I appreciate that!

New Job

Sat, 23 Mar 2024 15:42:10 +0200

At 2024-03-12 I started at chronosphere.io, the M3DB team. The team is focusing on efficiency of M3DB storage engine, and it so happens that the team I joined are performance nerds. I have never seen so many flamegraphs and profiler visualizations during a such short time span, which, given the team’s position in the company, shouldn’t come as a surprise.

To date, I am the first Linux (desktop) user in EMEA. So far I made 2 pull requests, which made Monorepo buildable and runnable on my environment. I will pick up the first “real” task next Monday.

11sync.net Signup

Sat, 23 Mar 2024 15:20:47 +0200

As some of you may have already noticed, I have launched a pre-registration page for 11sync.net. Here is it’s headline:

11sync.net is a Hosted Syncthing peer. Designed for Syncthing users seeking reliable backups and resilience.

I came up with the idea after running syncthing semi-manually for a few years now. At certain times I want to have a bootstrapped start-up of my own, and this feels like something I want to and would be skilled to do.

Thank You Drew DeVault

Sat, 23 Mar 2024 14:50:33 +0200

This is a long-overdue public thank-you letter to Drew DeVault.

He has been an ethical FOSS steward for as long as I remember. There is a number of examples where he stands for what’s right and upholds his values. Sometimes, perhaps unfortunately, pretty damn often, getting shit for it. Negativity on the internet doesn’t seem to stop him: it obviously makes him feel worse, but he persists and keeps doing what is right.

This conversation totally didn't happen at Microsoft

Thu, 07 Dec 2023 14:00:00 +0200

Similarity to real–world events and character names is coincidental.

Characters, Microsoft employees:

Amy: a high-level executive. Ex-JPMorgan. Pragmatic.
Harry: an engineer in Developer Services team. His organization owns code hosting, developer tools and CI infrastructure. A good listener.

2015 — the beginning of Git at Microsoft

Exchange between Harry and Amy in a parking lot of a chilly Redmond morning:

Harry: Amy, our Skype colleagues from Tallinn have been using git since 2006 and are making fun of us for using perforce in 2015. Our ex-AWS colleagues take offense, since they know Estonians are right. In fact, everyone takes offense, because nobody likes to admit Estonians are right. Git is a tad too slow for large repos, preventing quick migration. Do you mind if I ask my team to take a look into this?
Amy: sure, go ahead, Harry. I don’t care about version control, do what you think is right as long as it works for everyone.

Harry starts poking at git to make it work better for larger repositories.

My Declining Matrix usage

Thu, 31 Aug 2023 09:00:19 +0300

This post explains my journey with Matrix/Element. Here is a short timeline:

2020 November: read A Matrix overview on LWN and installed on my home server. Added Messenger, Hangouts and WhatsApp bridges. “Bridges” meant that I could read and write messages from FB Messenger, Google Hangouts and WhatsApp using a single application — Element (the application for the Matrix network). After 2 evenings of installation hurdles I conveniently reduced the number of browser tabs and phone applications I use for messaging.
2021 February: convinced my brother to move to Element. Conversations between us (which are second-in-volume after my wife) were now hosted by me.
2021 April: rest of the family to moved to Matrix. Much-reduced usage of WhatsApp, Messenger and Hangouts. It felt great and liberating!
2023 July: switched my family to Signal.

First year of Matrix was promising. Matrix posted good news about adoption to their blog. I followed them closely in conferences (you can see my name in one of the screenshots here!).

Nixos Subjectively

Thu, 31 Aug 2023 08:30:14 +0300

Previously I bloggged about the cool things I did with NixOS. After publishing the post, my friend Anton promptly asked:

Wondering what’s your professional take on NixOS. Would you give it a short for a small-to-medium size server fleet provisioning? It felt rather involved and not very mature when I looked at it. Kind of a commitment, too.

Here is my response:

My journey to NixOS has been bumpy ride: it’s been over a year since I looked at first, and I still sometimes feel I did not escape the beginner level. The learning curve is steep, and it is best to take it on gently or have a good mentor nearby. I started by installing NixOS on my primary laptop, which was a mistake. The annoyance of “I can do this in Debian in 5 seconds, and I am an hour in without an end of sight in this thing” was very discouraging at times.

End of Summer 2023

Sun, 27 Aug 2023 15:37:00 +0300

Just before this summer I laid out my roadmap for, well, the summer. Here is a quick retrospective. Weird order, because it is somewhat chronological. This post does not offer background for the project, so the previous post is a prerequisite reading.

Project 2: my take on universal headers

During SYCL 2023 I was told that Johny Marler expressed explicit interest in the project. I have much higher hopes in him than myself — at which point I decided to shelve universal-headers. Non-ironically, I am no longer working on compiling lots of C++ code, so this area has less ROI than it did back in the day at Uber.

Summer Roadmap 2023

Mon, 15 May 2023 08:38:08 +0300

Now that I have 6 weeks of employment remaining, my wife encouraged me to come up with something to do for the summer, and possibly after it. This post will list a few ideas I’ve been thinking about.

Next 6 weeks of employment

The roadmap described 6 weeks ago is still mostly applicable. Quick update:

The blog post I have mentioned has been published. Hooray.
For the next 6 weeks I will work on making the Zig/Go ecosystem as best as I can. Many thanks to my leadership for understanding the long-term importance of this initiative.
I have de-prioritized hermetic_cc_toolchain’s MacOS target support.

With employment out of the way, what is waiting for me past June 30?

My Zig and Go work for the next 3 months

Fri, 24 Mar 2023 19:10:12 +0200

Now that Uber uses “zig cc” to compile it’s Go Monorepo, here is a sneak preview of what I have planned for the next 3 months on the Zig/Go side:

Finish an “official” Uber’s blog post about how Uber uses zig and why. The content will be similar to my post a year ago, but with the milestones closed. Since the previous post we have enabled zig-cc as the default C/C++ compiler for CI, dev and production, our toolchain got open sourced and the company has committed to maintaining it. We still find bugs in Zig and Go and interaction between both though, so there is still work to be done.
Play around with MacOS target support for the mentioned toolchain. I can’t promise anything, but at least I want to evaluate the feasibility. This needs a bit of ground work on the toolchain side plus a lot of testing.
Make all Go tests pass with CC="zig cc". This is a prerequisite for the next goal.
Propose and, if accepted, implement an official CI node that tests Go with “zig cc” as the C compiler for linux/amd64 and linux/arm64. When this is done, the Go team will be alerted of regressions that impact “zig cc” users during the change. At the moment, unfortunately, if Go has a regression that impacts “zig cc”, the Go team learns about it only when someone (we?) attempt to upgrade Go to the latest release.
Extension from the above: do the same for macos. This would have caught this issue way before the release of Go 1.20; it will now be fixed only in Go 1.20.3.

If you are my (ex-)colleague that is/was involved, thank you very much. We have such an amazing team that was able to pull this off.

7 Years at Uber

Fri, 10 Feb 2023 01:54:23 +0200

This month turned 7 years since I joined Uber. Since it will be the last (a bit more on it in the next paragraph), I though it’s good to write a retrospective on how it looked like.

On 2022-09-07 it was announced that Uber engineering site will be shut down on 2023-06-30. Whoever is willing to relocate are welcome to do so. The rest will be laid off. The “easiest” offices for relocation are where our organization is: Aarhus, Amsterdam, Seattle, New York, Sunnyvale and San Francisco. In my case, I have a good life in Vilnius and want to keep it that way. So my days are numbered.

My Favorite Podcast

Wed, 30 Nov 2022 23:40:27 +0200

The only podcast I was able to listen for more than 3 series was BBC: mostly “history” and “life stories”. Over the last ~10 years I tried many others, but nothing clicked for a longer engagement.

A few months ago I stumbled across Adam Gordon Bell’s corecursive. My first episode was with Richard Hipp, the creator of SQLite. It was great. The second one was with about zig. The average episode is so good that I just downloaded them all to slowly go through them.

Side project retrospective

Sun, 21 Aug 2022 06:15:56 +0300

I spent 7 months building a project (hosted here). Goal: make a fastest known user/group NSS database. I succeeded, kinda. Here is an excerpt from a conclusion I wrote this morning:

This is the fastest known NSS passwd/group implementation for *reads*. On a
corpus with 10k users, 10k groups and 500 average members per group, `id`
takes 17 seconds with the glibc default implementation, 10-17 milliseconds
with a pre-cached `nscd`, ~8 milliseconds with `turbonss`.

Guess what? It is fastest, but not by enough (compared to nscd) to matter.

Uber Mock Interview Retrospective

Fri, 01 Jul 2022 12:55:00 +0300

Like mentioned in the previous post, I did a public mock coding interview. A reminder what that was:

The goal was to explain how some bits of Uber’s tech recruiting works.
The meetup page had 602 attendees as of writing. We expected quite a few participants in the event.

The mock interview consisted of:

Introduction by Uber’s EMEA recruiter Courtney Cox.
Myself doing a coding challenge with a 50 minute cap:
- I did not know the exercise upfront.
- Although my job did not depend on it, the ticking timer and people looking at my work (~260) made it quite stressful.
- I did not complete the exercise. According to my interviewee, I failed the “phone screen”. The good part is that I still get to keep my job. :)
Half-hour QA session.

TLDR: Highlights

Lots of fun for everyone: myself, the interviewer and the spectators.
Folks seemed to be engaged: the chat room was active throughout, and we had more questions than time to answer them.
Even though I have been coding Zig for the last few months, I felt like I had a strong enough grip on it; the algorithm was the one that tripped me.

TLDR: Lowlights

Most importantly, I did not complete the exercise. Worse, I did not even come up with the correct algorithm, therefore the interview was an obvious failure. I can re-apply in 6 months though!

In Defense Of Big Tech Hiring

Thu, 23 Jun 2022 13:45:00 +0300

There is quite a lot of negative sentiment about broken BigTech hiring processes. If you have not heard, these are good introductory posts:

The gist of the posts above is:

BigTech hiring process is pretty much the same across BigTech. It is explained in this post, even, in detail. Therefore, the companies are applying the same criteria, and thus fighting for the same candidates: the candidates that do well in these particular interviews, but not necessarily at the job.
Because the filter is the same, it does not encourage diversity in candidate background.
The interview process, and especially the problems, are not representative to what the dayjob will require. Some links above offer alternative methods of interviewing.

Why am I writing about this? I will be conducting an Uber Mock Interview later this month. I meant to write about seemingly broken BigTech interviews for a while now, but this event offered me a concrete deadline. I feel like I have to explain to myself why I am doing an interview at all, and why I am OK with the format we are planning to use. In this post I will:

How Uber Uses Zig

Mon, 23 May 2022 16:06:05 +0300

Disclaimer: I work at Uber and am partially responsible for bringing zig cc to serious internal use. Opinions are mine, this blog post is not affiliated with Uber.

I talked at the Zig Milan meetup about “Onboarding Zig at Uber”. This post is a little about “how Uber uses Zig”, and more about “my experience of bringing Zig to Uber”, from both technical and social aspects.

The video is here. The rest of the post is a loose transcript, with some commentary and errata.

Smart Bundling

Thu, 12 May 2022 05:55:00 +0300

TLDR

Could our package managers bundle our dependencies in git so it’s robust and frictionless? What about this:

“smart” vendoring to protect ourselves from things disappearing off the internet, and
write/have tools that make this vendoring easy for us.

Update 2022-02

Zig’s upcoming package manager will have ability to use bundled dependencies from the local checkout: exactly how it’s envisioned in the remainder of the article. Details in ziglang/zig#14293. Looking forward!

Number of dependencies

All of the programming languages I’ve used professionally, the names of which do not start with “c”¹, have package managers², which make “dependency management” easy. These package managers will, as part of the project’s build process, download and build dependencies. They are easy enough to use that there is virtually no resistance to add dependencies when they deem necessary.

First Post Here

Mon, 11 Apr 2022 18:16:36 +0300

This is the first post of the third iteration of jakstys.lt. The me-human is still changing, so do my public platforms.