CSV is a file format and Arrow is an in memory data format.

The CSV vs Parquet comparison makes more sense. Conflating Arrow / Parquet is a pet peeve of Wes: https://news.ycombinator.com/item?id=23970586

To be fair, arrow absorbed parquet-cpp, so a little confusion is to be expected.

The worst part about CSV is that it appears to be so simple that many people don't even try to understand how complicated it is and just roll their own broken dialect instead of just using a library. There is also no standardized encoding. Delimiters have to be negotiated out of band and people love getting them wrong.

Mostly agree, but RFC-4180 does specify delimiters. I've used pipe-delimited files for years to ensure explicitly-defined conformity, but recently due to the plethora of libraries have been thinking that CSV may be simpler.

The closest competitor would be HDF5, not Protobuf.

Seems nice. How does it compare to hdf5?

HDF5 is pretty terrible as a wire format, so it's not a 1-1 comparison to Arrow. Generally people are not going to be saving Arrow data to disk either (though you can with the IPC format), but serializing to a more compact representation like Parquet.

As I understand, arrow is particularly interesting since it’s wire format can be immediately queried/operated on without deserialization. Would saving an Arrow-structure as parquet not defeat that purpose, since your would need the costly deserialization step again on read? Honest question

The FAQ [1] and this SO answer [2] explain it better than I can, but basically yes. However, the (de)serialization overhead is probably better than most alternative formats you could save to.

[1] https://arrow.apache.org/faq/ [2] https://stackoverflow.com/questions/56472727/difference-betw...