feat(udf): minimal Python UDF SDK

[wangrunji0408]

I hereby agree to the terms of the RisingWave Labs, Inc. Contributor License Agreement.

What's changed and what's your intention?

This PR designs a minimal SDK for Python UDFs.

Now you can define a function in Python like this:

from risingwave.udf import udf, UdfServer

@udf(input_types=['INT', 'INT'], result_type='INT')
 def gcd(x: int, y: int) -> int:
     while y != 0:
         (x, y) = (y, x % y)
     return x

if __name__ == '__main__':
     server = UdfServer()
     server.add_function(gcd)
     server.serve()

This PR also fixes the problem when functions have no input arguments.

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features).
• I have demonstrated that backward compatibility is not broken by breaking changes and created issues to track deprecated features to be removed in the future. (Please refer to the issue)
• All checks passed in ./risedev check (or alias, ./risedev c)

Documentation

• My PR DOES NOT contain user-facing changes.

[xxchan]

lgtm

[xxchan]

What about creating a function with the same name as a build-in function? 🥵

[wangrunji0408]

At present, the creation will succeed but the usage will still refer to the built-in version. I will fix it later. 🥵

[BugenZhao]

🚀🚀🚀

[BugenZhao]

What about extracting this snippet to make the naming consistent everywhere? Like...

risingwave/src/frontend/src/handler/create_function.rs

Lines 86 to 97 in 896d92e

	// check if function exists
	if (session.env().catalog_reader().read_guard())
	.get_schema_by_id(&database_id, &schema_id)?
	.get_function_by_name_args(&function_name, &arg_types)
	.is_some()
	{
	let name = format!(
	"{function_name}({})",
	arg_types.iter().map(|t| t.to_string()).join(",")
	);
	return Err(CatalogError::Duplicated("function", name).into());
	}

[wangrunji0408]

Good idea! But this snippet will be deprecated soon. I'm going to decouple the function name between kernel and UDF server in the next PR. The syntax of CREATE FUNCTION will be changed correspondingly to:

create function gcd(int, int) returns int language python as gcd using link 'http://localhost:8815';

where gcd(int,int) is the name in kernel and gcd is the name in UDF server.

This approach refers to Flink and I think it's better than force unified name. 🤔

[codecov]

Codecov Report

Merging #7943 (5408f80) into main (f11bb62) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #7943      +/-   ##
==========================================
- Coverage   71.46%   71.45%   -0.01%     
==========================================
  Files        1128     1128              
  Lines      182535   182542       +7     
==========================================
- Hits       130445   130433      -12     
- Misses      52090    52109      +19     

Flag	Coverage Δ
rust	71.45% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/expr/src/expr/expr_udf.rs	0.00% <0.00%> (ø)
src/udf/src/lib.rs	1.72% <0.00%> (-0.10%)	⬇️
src/batch/src/executor/group_top_n.rs	68.23% <0.00%> (-6.48%)	⬇️
...frontend/src/scheduler/hummock_snapshot_manager.rs	60.00% <0.00%> (-0.48%)	⬇️
src/storage/src/hummock/compactor/mod.rs	80.69% <0.00%> (-0.20%)	⬇️
src/common/src/types/ordered_float.rs	31.06% <0.00%> (+0.19%)	⬆️

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