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jeffffffon I wrote an bash enumerator because I was sick of xargs

y'all still write shell commands manually?

jeffffffon Ford rehires 350 engineers after AI fails to preserve expertise or train juniors

porsche is part of volkswagen, so it's not that surprising that they're decently reliable. i probably see 10 porsches for every ferrari, lamborghini, etc that i see, and i think a large part of that is reliability - even absurdly rich people don't want to deal with an unreliable car when there is a more reliable alternative.

jeffffffon Everything in C is undefined behavior

Compilation error

jeffffffon Do you even need a database?

don't forget to fsync the file before the rename! and you also need to fsync the directory after the rename!

jeffffffon Apple discontinues the Mac Pro

> None of the things people care about really get much out of "unified memory". GPUs need a lot of memory bandwidth, but CPUs generally don't and it's rare to find something which is memory bandwidth bound on a CPU that doesn't run better on a GPU to begin with. Not having to copy data between the CPU and GPU is nice on paper but again there isn't much in the way of workloads where that was a significant bottleneck.

the bottleneck in lots of database workloads is memory bandwidth. for example, hash join performance with a build side table that doesn't fit in L2 cache. if you analyze this workload with perf, assuming you have a well written hash join implementation, you will see something like 0.1 instructions per cycle, and the memory bandwidth will be completely maxed out.

similarly, while there have been some attempts at GPU accelerated databases, they have mostly failed exactly because the cost of moving data from the CPU to the GPU is too high to be worth it.

i wish aws and the other cloud providers would offer arm servers with apple m-series levels of memory bandwidth per core, it would be a game changer for analytical databases. i also wish they would offer local NVMe drives with reasonable bandwidth - the current offerings are terrible (https://databasearchitects.blogspot.com/2024/02/ssds-have-be...)

jeffffffon Mongo but on Postgres and with strong consistency benefits

it's kind of dumb that postgres uses a nested loop join instead of a hash join there. hash join almost always has the best worst-case behavior, and without stats it should be the default choice.

jeffffffon Digital Wood Joints

we're not really close, for two reasons:

1) programming takes a long time, and it only makes sense to take the time to do it if you're making a bunch of copies of something. this is something that could be improved with better software and ux - if cad programs made it easy to just drag and drop joints from a joint library into your model then this would be a different story. a hardware+software solution could also work here, something like a cnc version of https://www.woodpeck.com/multi-router-group.html where the software makes it easy to scale the templates to your work piece.

2) setup takes a long time on the affordable machines. every time you change bits you have to recalibrate. positioning the work piece on the table and clamping/taping it down takes a lot of time. if you have to flip the work piece over then that takes even longer and positioning is even more critical, and programming is more complicated as well. regardless of whether your designs require cutting on one or both sides, you have to program tabs into your design so the router doesn't cut all the way through (or else the piece will move and the router will screw it up), and then you have to go back and cut the pieces out the rest of the way manually and trim off the tabs with a flush trim router bit. the high end production quality machines mitigate a lot of these issues, but now you are talking about a machine that costs at least $100,000 and takes up a whole room.

jeffffffon Digital Wood Joints

i'm a hobbyist woodworker with more money than time. i have a pretty basic 3-axis cnc and i thought it would save me time, but it really doesn't. the only thing i actually use it for is cutting out router templates, and even that would be done better with a laser cutter (although a good laser cutter costs a lot more than my cnc).

i could see how a machine big enough for 4x8 sheets with an automatic tool changer, a vacuum table, and all the automatic calibration gizmos might be a time saver for a production shop, but if you're building something that's a one-off or you don't have all the setup automation goodies (which are $$$$$) then setup and programming usually end up taking longer than doing the work the old fashioned way.

for tenon cutting like in the bed rail example you gave, i have a hard time imagining any situation where cnc is going to be more efficient than a domino xl.

jeffffffon Ask HN: Any felons successfully found IT work post-release?

Speaking of Indeed, the first employee (https://en.wikipedia.org/wiki/Chris_Lamprecht) was a felon and a great engineer

jeffffffon Zenbleed

shouldn't have any effect, the new amd hardware is zen 4 and this only affects zen 2

jeffffffon Backend of Meta Threads is built with Python 3.10

JIT compilation has the opportunity to do profile-guided optimization at runtime. JIT compilation is also simpler when distributing an application to non-identical servers, as it can optimize for the exact hardware it is running on.

jeffffffon Are You Sure You Want to Use MMAP in Your Database Management System? (2022)

take a look at http://nms.csail.mit.edu/~stavros/pubs/OLTP_sigmod08.pdf - the overhead of coordinating multiple writers often makes multi-writer databases slower than single-writer databases. remember, everything has to be serialized when it goes to the write ahead log, so as long as you can do the database updates as fast as you can write to the log then concurrent writers are of no benefit.

jeffffffon Dynamic bit shuffle using AVX-512

there are only a handful of instructions that do interesting things beyond parallel versions of basic arithmetic and bitwise operations. https://branchfree.org/2019/05/29/why-ice-lake-is-important-... provides a good overview of them.

jeffffffon Dynamic bit shuffle using AVX-512

AVX and AVX2 are pretty awful because of lane-crossing limitations, but AVX512 is actually really nice and feels like a real programmer designed it rather than an electrical engineer.

jeffffffon What every programmer should know about memory (2007) [pdf]

one thing that is missing from this document is that there are a limited number of line fill buffers in the L1 cache of each core, which limits the number of concurrent memory accesses that can be in flight well before anything related to channels/ranks/banks begins to matter. https://lemire.me/blog/2018/11/05/measuring-the-memory-level...

jeffffffon Smart ovens shouting out to servers in Russia and China

i have jenn air appliances and tried to connect to my dishwasher solely because i was curious as to why anyone would want their dishwasher to be connected to the internet. i could never get it to actually work, so i am still in the dark as to what i am missing out on in the world of internet connected dishwashers.

jeffffffon Ask HN: GDPR in 2022 – What do I need to know as a solo founder?

you'd have to block california too because CCPA is essentially the same thing

jeffffffon New integer types I’d like to see

the "if constexpr" makes sure the checks only happen in debug mode. you'd definitely want to turn the checks off for release builds.

jeffffffon New integer types I’d like to see

of course the standard allows implementations to "behave during translation or program execution in a documented manner characteristic of the environment" if you do something that is undefined behavior, implementations are literally allowed to do anything they want if you do something that is undefined behavior. the key point is that they are not required to do anything, so what's the point of adding more undefined behavior for this case?

jeffffffon New integer types I’d like to see

i think you could actually do that in C++ as a library with a bit of metaprogramming. the arithmetic operations will get weird though unless everything is the same type, for example what is the result type of int<-10, 10>+int<0, 20>? (the "right" answer is probably a megabyte of compiler errors)

jeffffffon New integer types I’d like to see

torstenvl is correct. UB is UB whether you are in debug mode or release mode. making it UB for it to store a negative value doesn't make sense. you could put debug checks for it behind an if constexpr or a macro but please C++ has enough UB already, don't add more. disappointing to see that this is downvoted.

jeffffffon New integer types I’d like to see

the one about unsigned integers with one bit missing would be trivial to implement as a library in C++ with no significant downside. all you have to do is make a class wrapping a signed int and put debug checks for if the high 1 bit is set behind an if constexpr in operator= and the copy constructor. in most other languages this would bring a big performance penalty, but this is one thing that C++ is actually very good at.

jeffffffon Bank of America Email: “Update Your iPhone”

most people who are hesitant to update are hesitant because they've been burned in the past. apple has a history of making phones unusably slow with updates and breaking 3rd party software.

jeffffffon AWS switch from gzip to zstd – about 30% reduction in compressed S3 storage

well i tried. i wish you the best of luck in your continued ignorance.

jeffffffon AWS switch from gzip to zstd – about 30% reduction in compressed S3 storage

if it's not in ram, you have to do an extra IO to look it up. i don't think you understand how precious metadata space is in a large scale storage system. if you pollute the metadata cache with useless junk like this, you can't cache as many things, your hit rate goes down, and you have to do more IO operations to service each request on average. name one popular distributed file system or object store that compresses everything by default like you are claiming. you won't be able to, because none of them do it, because it's better to leave it to the application.

jeffffffon AWS switch from gzip to zstd – about 30% reduction in compressed S3 storage

https://www.reddit.com/r/programming/comments/wtd61q/aws_swi...

this tweet is not talking about compressing customer data in s3, i seriously doubt that aws compresses customer data in s3 for all the reasons i've already listed. i am right and amazon does know what they're doing, which is why they don't compress customer data in s3.

4 bytes per megabyte becomes significant at scale when you have to keep it in ram, which you have to do if you want to avoid the extra IO.

jeffffffon AWS switch from gzip to zstd – about 30% reduction in compressed S3 storage

yeah that isn't free either, it adds significant bloat to your metadata. with most enterprise customers encrypting and/or compressing data before putting it into s3, it doesn't seem like there would be much benefit. s3 really isn't the right layer to implement compression. filesystems aren't either. it's better to leave it up to the application.

jeffffffon AWS switch from gzip to zstd – about 30% reduction in compressed S3 storage

But if you do need to seek, which is really common in data warehouse workloads for example, unless you keep the index in ram you have to do an extra IO on every seek to read the index

jeffffffon AWS switch from gzip to zstd – about 30% reduction in compressed S3 storage

Sure, but now you've added an extra layer of indirection which can have a significant impact on performance

jeffffffon Ask HN: Who is using C++ as the main language for new project?

yeah maybe my message wasn't clear, i was trying to say that you should read both, the old one is still valuable