I think I can help answer these: 1) LLVM IR is an intermediate representation for compilers, WASM is an open standard for sandboxed computation. They fulfill different but complimentary roles. If the query engine were handed LLVM IR, it would still have to JIT the IR to wasm in order to maintain the sandboxing guarantees. It would also tie the query engine to LLVM, whereas there may be other wasm generators out there.
2) The idea would be for the user to use some external tool or compiler that generates wasm, and pass the wasm to the query engine. This would mean that you could write a UDF in any language of your choosing. It seems like it wouldn’t be much work to use your existing numpy + numba pipeline as well, you would just have to add a step to generate wasm from your LLVM IR before passing it to the engine. Sasha > 26 апр. 2022 г., в 10:39, Li Jin <[email protected]> написал(а): > > This is a very interesting topic and one that we care a lot about when > using/thinking about Arrow compute. > > I come from Python data analytics where most of our users use Pandas/Numpy. > This is also my first time learning about WASM and my previous > understanding of "Python UDF in Arrow C++ compute" engine is more of: > > UDF written in NumPy API -> Using Numba to compile UDF into LLVM IR -> > Execute LLVM IR within Arrow C++ engine on Arrow Arrays > > Which in my understanding is similar to UDFs in Impala with LLVM IR that > Wes mentioned. > > I wonder how WASM potentially changing things. A couple of questions: > (1) What is the advantage of using WASM instead of sth like LLVM IR? > (2) Do we envision using sth like a NumPy API as the language that writes > these UDFs or sth completely different? (Another DSL?) > > Li > >> On Tue, Apr 26, 2022 at 11:04 AM Weston Pace <[email protected]> wrote: >> >> In addition to the memory copy it looks like WASM is going to bounds >> check all loads/stores. It does, at least, have some vectorized >> load/store operations so that can help amortize the cost. It appears >> you aren't going to get the same performance as native today using >> WASM but I'm guessing that is an active area of research and >> investment. >> >>> On Tue, Apr 26, 2022 at 5:00 AM Jorge Cardoso Leitão >>> <[email protected]> wrote: >>> >>> I need to correct myself here - it is currently not possible to pass >> memory >>> at zero cost between the engine and WASM interpreter. This is related to >>> your point about safety - WASM provides memory safety guarantees because >> it >>> controls the memory region that it can read from and write to. Therefore, >>> currently passing data from and into WASM requires a memcopy. >>> >>> There is a proposal [1] to improve the situation, but currently would >> incur >>> a cost in the query engine, since we would need to memcopy the regions >>> around. >>> >>> I forgot that on my poc I passed the parquet file from js to WASM and >>> de-serialized it to arrow directly in wasm - so memory was already being >>> allocated from within WASM sandbox, not JS. Sorry for the confusion. >>> >>> [1] https://github.com/WebAssembly/design/issues/1439 >>> >>> Best, >>> Jorge >>> >>> >>> >>> On Tue, Apr 26, 2022 at 3:43 PM Antoine Pitrou <[email protected]> >> wrote: >>> >>>> >>>> Le 26/04/2022 à 16:30, Gavin Ray a écrit : >>>>> Antoine, sandboxing comes into play from two places: >>>>> >>>>> 1) The WASM specification itself, which puts a bounds on the types of >>>>> behaviors possible >>>>> 2) The implementation of the WASM bytecode interpreter chosen, like >> Jorge >>>>> mentioned in the comment above >>>>> >>>>> The wasmtime docs have a pretty solid section covering the sandboxing >>>>> guarantees of WASM, and then the interpreter-specific >> behavior/abilities >>>> of >>>>> wasmtime FWIW: >>>>> https://docs.wasmtime.dev/security-sandboxing.html#webassembly-core >>>> >>>> This doesn't really answer my question, does it? >>>> >>>> >>>>> >>>>> On Tue, Apr 26, 2022 at 10:22 AM Antoine Pitrou <[email protected]> >>>> wrote: >>>>> >>>>>> >>>>>> Le 26/04/2022 à 16:18, Jorge Cardoso Leitão a écrit : >>>>>>>> Would WASM be able to interact in-process with non-WASM buffers >>>> safely? >>>>>>> >>>>>>> AFAIK yes. My understanding from playing with it in JS is that a >>>>>>> WASM-backed udf execution would be something like: >>>>>>> >>>>>>> 1. compile the C++/Rust/etc UDF to WASM (a binary format) >>>>>>> 2. provide a small WASM-compiled middleware of the c data interface >>>> that >>>>>>> consumes (binary, c data interface pointers) >>>>>>> 3. ship a WASM interpreter as part of the query engine >>>>>>> 4. pass binary and c data interface pointers from the query engine >>>>>> program >>>>>>> to the interpreter with WASM-compiled middleware >>>>>> >>>>>> Ok, but the key word in my question was "safely". What mechanisms >> are in >>>>>> place such that the WASM user function will not access Arrow >> buffers out >>>>>> of bounds? Nothing really stands out in >>>>>> https://webassembly.github.io/spec/core/index.html, but it's the >> first >>>>>> time I try to have a look at the WebAssembly spec. >>>>>> >>>>>> Regards >>>>>> >>>>>> Antoine. >>>>>> >>>>>> >>>>>>> >>>>>>> Step 2 is necessary to read the buffers from FFI and output the >> result >>>>>> back >>>>>>> from the interpreter once the UDF is done, similar to what we do in >>>>>>> datafusion to run Python from Rust. In the case of datafusion the >>>>>> "binary" >>>>>>> is a Python function, which has security implications since the >> Python >>>>>>> interpreter allows everything by default. >>>>>>> >>>>>>> Best, >>>>>>> Jorge >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Tue, Apr 26, 2022 at 2:56 PM Antoine Pitrou <[email protected] >>> >>>>>> wrote: >>>>>>> >>>>>>>> >>>>>>>> Le 25/04/2022 à 23:04, David Li a écrit : >>>>>>>>> The WebAssembly documentation has a rundown of the techniques >> used: >>>>>>>> https://webassembly.org/docs/security/ >>>>>>>>> >>>>>>>>> I think usually you would run WASM in-process, though we could >> indeed >>>>>>>> also put it in a subprocess to further isolate things. >>>>>>>> >>>>>>>> Would WASM be able to interact in-process with non-WASM buffers >>>> safely? >>>>>>>> It's not obvious from reading the page above. >>>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>>> It would be interesting to define the Flight "harness" protocol. >>>>>>>> Handling heterogeneous arguments may require some evolution in >> Flight >>>>>> (e.g. >>>>>>>> if the function is non scalar and arguments are of different >> length - >>>>>> we'd >>>>>>>> need something like the ColumnBag proposal, so this might be a >> good >>>>>> reason >>>>>>>> to revive that). >>>>>>>>> >>>>>>>>> On Mon, Apr 25, 2022, at 16:35, Antoine Pitrou wrote: >>>>>>>>>> Le 25/04/2022 à 22:19, Wes McKinney a écrit : >>>>>>>>>>> I was going to reply to this e-mail thread on user@ but >> thought I >>>>>>>>>>> would start a new thread on dev@. >>>>>>>>>>> >>>>>>>>>>> Executing user-defined functions in memory, especially >> untrusted >>>>>>>>>>> functions, in general is unsafe. For "trusted" functions, >> having an >>>>>>>>>>> in-memory API for writing them in user languages is very >> useful. I >>>>>>>>>>> remember tinkering with adding UDFs in Impala with LLVM IR, >> which >>>>>>>>>>> would allow UDFs to have performance consistent with built-ins >>>>>>>>>>> (because built-in functions are all inlined into code-generated >>>>>>>>>>> expressions), but segfaults would bring down the server, so >> only >>>>>>>>>>> admins could be trusted to add new UDFs. >>>>>>>>>>> >>>>>>>>>>> However, I wonder if we should eventually define an "external >> UDF" >>>>>>>>>>> protocol and an example UDF "harness", using Flight to do RPC >>>> across >>>>>>>>>>> the process boundaries. So the idea is that an external local >> UDF >>>>>>>>>>> Flight execution service is spun up, and then data is sent to >> the >>>> UDF >>>>>>>>>>> in a DoExchange call. >>>>>>>>>>> >>>>>>>>>>> As Jacques pointed out in an interview 1], a compelling >> solution to >>>>>>>>>>> the UDF sandboxing problem is WASM. This allows "untrusted" >> WASM >>>>>>>>>>> functions to be run safely in-process. >>>>>>>>>> >>>>>>>>>> How does the sandboxing work in this case? Is it simply >> executing >>>> in a >>>>>>>>>> separate process with restricted capabilities, or are other >>>> mechanisms >>>>>>>>>> put in place? >>>>>>>> >>>>>>> >>>>>> >>>>> >>>> >>
