SIMD for decimal data type

[liukun4515]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

From this datafusion issue, we will add the decimal data type
in the datafusion.
But some basic operations like +,- we implemented do not support SIMD.

In order to speed up the calculation, we need to add the SIMD feature for the decimal data type.

I have not figured out how to implement it.

Describe the solution you'd like
TODO

Describe alternatives you've considered
TODO

Additional context
TODO

[liukun4515]

please assign this to me.

[alamb]

FYI @liukun4515 -- before implementing explicit SIMD versions of these kernels, it may be worth doing some profiling / disassembly of what rustc creates for the current kernels.

Perhaps a good start would be to add Decimal support to the existing kernels in https://docs.rs/arrow/6.3.0/arrow/compute/kernels/aggregate/index.html if it doesn't alread exist

I have not reviewed the code in the datafusion aggregate functions for a while, so I am not familiar with how much they do / don't use the arrow compute kernels.

[liukun4515]

disassembly

Thanks for your suggestion, I will follow this.

[alamb]

FWIW I believe https://rust.godbolt.org/ is a popular tool for such work

[chadbrewbaker]

https://ispc.github.io etc are probably the way to go. For any expensive query you will want to shell out to LLVM and custom compile the worker binaries before the run - also probably blast the query plan with an SMT solver to reduce the expense/runtime depending on your constraints. I would avoid dynamic linking like the plague - be like the IBM Blue Gene/L.

[chadbrewbaker]

Before mucking with simd - probably good idea to have a repo like Rust coreutils that leverages existing regression tests for the SQL engine. Especially perf regressions.

https://github.com/postgres/postgres/tree/master/src/test/regress

https://github.com/s3team/Squirrel

[chadbrewbaker]

Here is the Google SIMD assembler https://github.com/google/zetasql/blob/master/zetasql/base/mathutil.h

[liukun4515]

@chadbrewbaker thanks.

[tustvold]

Implemented by #2881

[liukun4515]

Implemented by #2881

Thanks @tustvold