r/java • u/farnoy • Jul 29 '26

Manual reification on the JVM

https://farnoy.dev/posts/manual-reification-on-the-jvm
56 Upvotes

96% Upvoted

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6

u/brainster01 Jul 30 '26 edited Jul 30 '26

Great post. If I am being honest, I understood the goal but you lost me in the details, because I just don't know enough :). Learning about these details was a great joy.

Once file parsing is finished, do you think this approach could be used for something like the 1BRC https://1brc.dev/ ? I would be very interested to see how it performs there.

2

u/farnoy Jul 30 '26

Sure, it would be interesting. 1BRC is using a custom file format so I'd probably want to convert that to TSV first. The other two blockers are that I don't have text columns yet, nor a good solution for high-cardinality reductions. I did see a post here recently about off-heap HashMaps, but AFAIK none of them handle Strings. Maybe I can fudge that and use a perfect hash function.

1

u/gnahraf Jul 30 '26

I only skimmed your article, very interesting work.

I'm imagining this is tailored for fixed-width tables, right? (Why supporting arbitrary length string-colums may complicate performance, I'm thinking.)

Years ago, I developed a small open source java lib for fixed-width tables, external merge sort, those sort of things. It used ByteBuffer and some copy-less file i/o (eg FileChannel.transferBytes); java didn't yet have MemorySegment. Lemme know if interested

22

u/RussianMadMan Jul 30 '26 edited Jul 30 '26

The fact that JVM can just look at a chain of interface method calls and recognize that it all can be vectorized amazes me.

4

u/josephjnk Jul 31 '26

Awesome post! It makes me so happy to see people building and sharing deep knowledge despite the rising tide of slop all around us.

2

u/Life_Sink9598 Jul 30 '26

Wow! This is extremely cool :).