Comments (1)
pmarks
commented on September 24, 2024
On further investigation, I believe this is an incorrect report. It seems that the compression level isn't actually encoded in the parquet format, so when pqrs reports compression: ZSTD(ZstdLevel(1)), the 1 is a default value.
I also realized that the zstd does not produce better compression at level 10 on my example dataset. Here is an example that does work correctly:
import numpy as np
df = pl.DataFrame({"a": 10000 * np.arange(1000000).astype(np.float32), "b": 10000 * np.arange(1000000).astype(np.float32)})
df.write_parquet("z1.pq", statistics=True)
df.write_parquet("z20.pq", compression_level=20, statistics=True)```
in this example the z20 file is about 1/2 the size of the z1 file, but there are no changes in compression until you set compression_level>15.
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