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Mention that the sample of zstd_train_dict is chosen randomly #47

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phiresky merged 1 commit into from
Apr 30, 2025
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Mention that the sample of zstd_train_dict is chosen randomly #47

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4 changes: 2 additions & 2 deletions README.md
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Expand Up @@ -104,9 +104,9 @@ Note that a compression VFS such as https://github.com/mlin/sqlite_zstd_vfs migh

- `zstd_train_dict(agg, dict_size: int, sample_count: int) -> blob`

Aggregate function (like sum() or count()) to train a zstd dictionary on sample_count samples of the given aggregate data
Aggregate function (like sum() or count()) to train a zstd dictionary on randomly selected sample_count samples of the given aggregate data

Example use: `select zstd_train_dict(tbl.data, 100000, 1000) from tbl` will return a dictionary of size 100kB trained on 1000 samples in `tbl`
Example use: `select zstd_train_dict(tbl.data, 100000, 1000) from tbl` will return a dictionary of size 100kB trained on 1000 random samples in `tbl`

The recommended number of samples is 100x the target dictionary size. As an example, you can train a dict of 100kB with the "optimal" sample count as follows:

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