[jira] [Created] (ARROW-7252) [Rust] Reading UTF-8/JSON/ENUM field results in a lot of vec allocation

["Wong Shek Hei (Jira)" <ji...@apache.org>]

Wong Shek Hei created ARROW-7252:
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             Summary: [Rust] Reading UTF-8/JSON/ENUM field results in a lot of vec allocation
                 Key: ARROW-7252
                 URL: https://issues.apache.org/jira/browse/ARROW-7252
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Rust
            Reporter: Wong Shek Hei


While reading a very large parquet file with basically all string fields was very slow(430MB gzipped), after profiling with osx instruments, I noticed that a lot of time is spent in "convert_byte_array", in particular, "reserving" and allocating Vec::with_capacity, which is done before String::from_utf8_unchecked.

It seems like using String as the underlying storage is causing this(String uses Vec<u8> for its underlying storage), this also requires copying from slice to vec.

"Field::Str<String>" is a pub enum so I am not sure how "refactorable" is the String part, for example, converting it into a &str(we can perhaps then defer the conversion from &[u8] to Vec<u8> until the user really needs a String)

But of course, changing it to &str can result in quite a bit of interface changes... So I am wondering if there are already some plans or solution on the way to improve the handling of the "Field::Str" case?

 



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