Less salt #14173
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Less salt #14173
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Less salt (duckdb/duckdb#14173) [Python Dev] Make sure the GIL is released when the connection+db are being shut down (duckdb/duckdb#14113)
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Less salt (duckdb/duckdb#14173) [Python Dev] Make sure the GIL is released when the connection+db are being shut down (duckdb/duckdb#14113) Co-authored-by: krlmlr <krlmlr@users.noreply.github.com>
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Fixes #14389 and reverts #14173 (bringing back the salt). Although I don't think this should affect correctness (from cppreference.com): > When a compare-and-exchange is in a loop, the weak version will yield better performance on some platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the strong one is preferable. This gave us correctness issues with older GCC versions (< 10.x) on ARM64. We rarely use CAS operations, so this isn't a big diff. I've added `std::memory_order` to improve the performance (copying the usage in `concurrentqueue.h`). Since it is difficult to programmatically disable "incorrect" usage, I've added a comment in `atomic.hpp` that describes the issue. I've also changed usage of `MetadataPointer` to a const reference since older GCC versions were throwing a warning.
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Apparently ARM64v8 uses 52, not 48 bits for the pointer (not all versions of ARM64v8, but just some). We could also
#ifdefour way around this but this seems fine. It reduces the effectiveness of the salt by 16x sadly, but it's still reduces the chance of having to chase the pointer even when keys are different by 4096x (was 65536x).Fixes #14140