Andrew Lamb created ARROW-11002:
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Summary: [Rust] Improve speed of JSON nested list reader
Key: ARROW-11002
URL: https://issues.apache.org/jira/browse/ARROW-11002
Project: Apache Arrow
Issue Type: Improvement
Components: Rust
Reporter: Andrew Lamb
The code that reads in nested lists in rust/arrow/src/json/reader.rs does an
extra copy (via `Vec::clone`) that caused 20% slowdown in a benchmark compared
to not cloning.
The goal of this ticket would be to improve the performance of reading JSON in
this case, likely by avoiding the clone
More details can be found here:
https://github.com/apache/arrow/pull/8938#pullrequestreview-556273641
As [~nevi_me] says:
> I suspect the main perf loss is from having to peek into JSON values in order
> to make the nesting work.
> By this, I mean that if we have {"a": [_, _, _]}, we extract a values into a
> Vec<Value>, i.e. [_, _, _].
> By extracting values, we are able to then use the reader to read &[Value]
> without caring about its key (a).
> The downside of this approach is that we have to clone values to get
> Vec<Value>, as I couldn't find an alternative
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