Prototype for Join Ordering #18023
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Prototype for Join Ordering #18023
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| /// A simple Vec-based map that uses Option<T> for sparse storage | ||
| /// Keys are never reused once removed | ||
| pub(crate) struct VecMap<V>(Vec<Option<V>>); |
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I don't know if you heard about slab. It's the same as VecMap, but where you can reuse keys. However, I am unfamiliar with the process of pulling in external dependencies.
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I was using slotmap at first and also wasn't sure about the dependencies. And since we are not deleting notes, I thought the vecmap suffices.
And I mostly wanted to test the API of the query graph.
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And since we are not deleting notes, I thought the vecmap suffices.
Aha okay, than i have nothing to add here :)
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This is a draft PR to provide a basis for the discussion in issue #17719.
The main point of the PR is to get some experience for designing a JoinGraph structure. The PR pretends Datafusion already has a JoinGraph/QueryGraph implemented and tries to use its API for join order optimization.
It implements the closed form solution to calculating the optimal left-deep join tree developed by Ibaraki&Kameda: https://dl.acm.org/doi/pdf/10.1145/1270.1498
It is also presented here: https://youtu.be/CcUVvnYv7Hg?list=PLSE8ODhjZXjYCZfIbmEWH7f6MnYqyPwCE&t=1952
It can be used to obtain a reasonable join ordering in polynomial time or as a starting point for more sophisticated algorithms.