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Posted to github@arrow.apache.org by GitBox <gi...@apache.org> on 2021/07/04 19:17:43 UTC
[GitHub] [arrow-datafusion] houqp opened a new issue #677: Use a single HashMap implementation consistently across the code base
houqp opened a new issue #677:
URL: https://github.com/apache/arrow-datafusion/issues/677
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We are using both `std::collections::HashMap` and `hashbrown::HashMap` in datafusion, it would be better to consistently use only one of them.
hashbrown's official readme has the following statement:
> Since Rust 1.36, this is now the HashMap implementation for the Rust standard library. However you may still want to use this crate instead since it works in environments without std, such as embedded systems and kernels.
However, it's unclear whether Rust std also uses ahash as the default hasher. If not, it seems like hashbrown would still be a better choice when it comes to performance.
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**Additional context**
Follow up from https://github.com/apache/arrow-datafusion/pull/676#discussion_r663544711.
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[GitHub] [arrow-datafusion] alamb commented on issue #677: Use a single HashMap implementation consistently across the code base
Posted by GitBox <gi...@apache.org>.
alamb commented on issue #677:
URL: https://github.com/apache/arrow-datafusion/issues/677#issuecomment-874046165
`hashbrown::HashMap` is a good choice 👍 in my opinion
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[GitHub] [arrow-datafusion] alamb commented on issue #677: Use a single HashMap implementation consistently across the code base
Posted by GitBox <gi...@apache.org>.
alamb commented on issue #677:
URL: https://github.com/apache/arrow-datafusion/issues/677#issuecomment-874046165
`hashbrown::HashMap` is a good choice 👍 in my opinion
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[GitHub] [arrow-datafusion] Dandandan commented on issue #677: Use a single HashMap implementation consistently across the code base
Posted by GitBox <gi...@apache.org>.
Dandandan commented on issue #677:
URL: https://github.com/apache/arrow-datafusion/issues/677#issuecomment-873671789
The hash brown crate is used
* It exposes some more APIs like `RawEntry`, which can avoid hashing / looking up elements twice.
* It is slightly faster than the version included with Rust std, not only because of aHash (vs SipHasher used in std), but also some further optimizations / inlining.
I think best would be to define a `HashMap` type alias, so we can use whatever is set by default across the project.
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[GitHub] [arrow-datafusion] houqp commented on issue #677: Use a single HashMap implementation consistently across the code base
Posted by GitBox <gi...@apache.org>.
houqp commented on issue #677:
URL: https://github.com/apache/arrow-datafusion/issues/677#issuecomment-873871918
Agreed, I think we should move all HashMap import to our own pluggable type alias and set `hashbrown::HashMap` as the default.
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[GitHub] [arrow-datafusion] Dandandan edited a comment on issue #677: Use a single HashMap implementation consistently across the code base
Posted by GitBox <gi...@apache.org>.
Dandandan edited a comment on issue #677:
URL: https://github.com/apache/arrow-datafusion/issues/677#issuecomment-873671789
The hash brown crate is used for those reasons:
* It exposes some more APIs like `RawEntry`, which can avoid hashing / looking up elements twice.
* It is slightly faster than the version included with Rust std, not only because of aHash (vs SipHasher used in std), but also some further optimizations / inlining.
I think best would be to define a `HashMap` type alias, so we can use whatever is set by default across the project.
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