hashtable-benchmarks
STC
hashtable-benchmarks | STC | |
---|---|---|
8 | 89 | |
29 | 1,113 | |
- | 4.1% | |
4.7 | 9.1 | |
5 months ago | 27 days ago | |
Java | C | |
Apache License 2.0 | MIT License |
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hashtable-benchmarks
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Building a faster hash table for high performance SQL joins
Since the blog post mentioned a PR to replace linear probing with Robin Hood, I just wanted to mention that I found bidirectional linear probing to outperform Robin Hood across the board in my Java integer set benchmarks:
https://github.com/senderista/hashtable-benchmarks/blob/mast...
https://github.com/senderista/hashtable-benchmarks/wiki/64-b...
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Ask HN: Who wants to be hired? (December 2023)
https://homes.cs.washington.edu/~magda/papers/wang-cidr17.pd...
I'm most interested in developing high-performance database engines in low-level languages, but open to any challenging systems programming project. I've been working in C++ for the last 3 years, but have written nontrivial projects in Rust and Java as well (e.g., https://github.com/senderista/rotated-array-set, https://github.com/senderista/hashtable-benchmarks). I would enjoy using Rust or Zig on a new project, but I consider the project itself to be much more important than the language it's written in. I am not interested in cryptocurrency, adtech, or fintech projects.
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Factor is faster than Zig
Thanks for the details on your benchmarks. I would like sometime to extend BLP to a more generic setting; as I said I think any trick used with RH would also work with BLP. I just used an integer set because that's all I needed for my use case and it was easy to implement several different approaches for benchmarking. As you note, it favors use cases where the hash function is cheap (or invertible) and elements are cheap to move around.
About your question on load factors: no, the benchmarks are measuring exactly what they claim to be. The hash table constructor divides max data size by load factor to get the table size (https://github.com/senderista/hashtable-benchmarks/blob/mast...), and the benchmark code instantiates each hash table for exactly the measured data set size and load factor (https://github.com/senderista/hashtable-benchmarks/blob/mast...).
I can't explain the peaks around 1M in many of the plots; I didn't investigate them at the time and I don't have time now. It could be a JVM artifact, but I did try to use JMH "best practices", and there's no dynamic memory allocation or GC happening during the benchmark at all. It would be interesting to port these tables to Rust and repeat the measurements with Criterion. For more informative graphs I might try a log-linear approach: divide the intervals between the logarithmically spaced data sizes into a fixed number of subintervals (say 4).
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Inside boost::unordered_flat_map
I think "bidirectional linear probing" is an underrated approach (and much simpler): https://github.com/senderista/hashtable-benchmarks/blob/master/src/main/java/set/int64/BLPLongHashSet.java
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A fast & densely stored hashmap and hashset based on robin-hood backward shift deletion
I will probably never get around to porting my bidirectional linear probing integer hash set from Java to C++, but I hope someone can try adapting BLP to general C++ hashmaps and hashsets, because it significantly outperforms Robin Hood in my benchmarks.
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Ask HN: Who wants to be hired? (March 2022)
https://homes.cs.washington.edu/~magda/papers/wang-cidr17.pd...
I'm most interested in developing high-performance database engines in low-level languages, but open to any challenging systems programming project. I've been working in C++ for the last 2 years, but have written nontrivial projects in Rust and Java as well (e.g., https://github.com/senderista/rotated-array-set, https://github.com/senderista/hashtable-benchmarks). I would enjoy using Rust or Zig on a new project, but I consider the project itself to be much more important than the language it's written in. I am not interested in cryptocurrency, adtech, or fintech projects.
STC
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Macro to automatically unlock a mutex in a block (ansi c)
This technique is often used to implement RAII in C. See example in Standard Template Containers. The library delivers STL-like functionality to C.
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Is using void* considered "evil" in C just as it is in C++?
I'd say it's evil, but quite understandable very commonly used because there are no built-in alternatives in C. I basically never use void* in user-code, simply because there are no need for it when using a templating technique, like in my STC library. Even in the implementation of STC itself, void* is hardly used, if at all.
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Book recommendations for learning C really thoroughly
Study Other Peoples C Code and here's one that is easy to read: https://github.com/stclib/STC/releases
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[Noob Question] How do C programmers get around not having hash maps?
STC
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Should I use templates or stick with rewriting code?
This is more or less how C-ish templates are implemented in STC library.
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What’s the right hash table API?
As the author of a STL-like templated C container library, I had many of the exact same thoughts when implementing the unordered map. In fact, I also changed to many of the suggestions here, rather than consistently following the C++ umap API. E.g.
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What's the fastest high level language?
Sure it is. C misses a proper efficient generic standard/container library, like my https://github.com/stclib/STC, but that is irrelevant.
- STC v4.2 Released (note: new URL)
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Popular Data Structure Libraries in C ?
Smart Template Containers (STC)
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So what's the best data structures and algorithms library for C?
Some data structure and algorithm library in C enable the (optional) separation between the interface of the container (which is expanded in your header) and its implementation (which is expanded in your source), like STC.
What are some alternatives?
unordered_dense - A fast & densely stored hashmap and hashset based on robin-hood backward shift deletion
ctl - The C Template Library
myria - Myria is a scalable Analytics-as-a-Service platform based on relational algebra.
mlib - Library of generic and type safe containers in pure C language (C99 or C11) for a wide collection of container (comparable to the C++ STL).
js2scheme
Klib - A standalone and lightweight C library
flat_hash_map - A very fast hashtable
ctl - My variant of the C Template Library
robin-hood-hashing - Fast & memory efficient hashtable based on robin hood hashing for C++11/14/17/20
CommonC - Common utilities for C
nafeez.xyz - ⚡ My personal website.
ccan - The C Code Archive Network