https://github.com/bytehamster/pachash

Packed and Compressed Hash Tables
https://github.com/bytehamster/pachash

Last synced: 2 months ago
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Packed and Compressed Hash Tables

• Host: GitHub
• URL: https://github.com/bytehamster/pachash
• Owner: ByteHamster
• License: gpl-3.0
• Created: 2021-12-15T14:10:26.000Z (about 3 years ago)
• Default Branch: main
• Last Pushed: 2023-11-21T16:20:50.000Z (about 1 year ago)
• Last Synced: 2024-06-12T17:57:35.150Z (6 months ago)
• Language: C++
• Homepage:
• Size: 933 KB
• Stars: 14
• Watchers: 5
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE
  • Citation: CITATION.cff

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README

        
# PaCHash

An object store for variable-sized objects, which has small internal-memory space usage

and still guarantees a limited number of external IO operations.

For a given parameter *a*, the internal memory space usage is *2 + log(a)* bits per block.

Queries for objects of size *|x|* take constant time and fetch *1 + |x|/B + 1/a* blocks from external memory.

[](https://arxiv.org/pdf/2205.04745)

### Library usage

Add the following to your `CMakeLists.txt`.

```

add_subdirectory(path/to/PaCHash)

target_link_libraries(YourTarget PRIVATE PaCHash)

```

### Building the examples

```

git clone --recursive [email protected]:ByteHamster/PaCHash.git

mkdir PaCHash/build

cd PaCHash/build

cmake -DCMAKE_BUILD_TYPE=Release ..

make -j

```

### Benchmarks

Alternative methods are implemented for benchmarking.

You can find the full benchmark scripts in an independent repository: https://github.com/ByteHamster/PaCHash-Experiments

| Method            | External memory utilization | Internal memory usage | IOs per query     |

|-------------------|-----------------------------|-----------------------|-------------------|

| PaCHash           | 100%                        | ~6 bits/page          | 1 (variable size) |

| Separator Hashing | Up to 98%¹                  | ~6 bits/page          | 1                 |

| Cuckoo Hashing    | Up to 98%¹                  | Constant              | 2 parallel        |

¹ Depending on the input distribution. The methods are originally designed for fixed size objects.

Adversarial input can therefore bring the utilization down to 51% or even make construction impossible.

### License

This code is licensed under the [GPLv3](/LICENSE).

If you use the project in an academic context or publication, please cite [our paper](https://doi.org/10.1137/1.9781611977561.ch14):

```

@inproceedings{kurpicz2023pachash,

  author       = {Florian Kurpicz and

                  Hans{-}Peter Lehmann and

                  Peter Sanders},

  title        = {PaCHash: Packed and Compressed Hash Tables},

  booktitle    = {{ALENEX}},

  pages        = {162--175},

  publisher    = {{SIAM}},

  year         = {2023},

  doi          = {10.1137/1.9781611977561.CH14}

}

```