make hash function in RepartitionExec configurable #17648
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| // Licensed to the Apache Software Foundation (ASF) under one | ||
| // or more contributor license agreements. See the NOTICE file | ||
| // distributed with this work for additional information | ||
| // regarding copyright ownership. The ASF licenses this file | ||
| // to you under the Apache License, Version 2.0 (the | ||
| // "License"); you may not use this file except in compliance | ||
| // with the License. You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, | ||
| // software distributed under the License is distributed on an | ||
| // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | ||
| // KIND, either express or implied. See the License for the | ||
| // specific language governing permissions and limitations | ||
| // under the License. | ||
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| //! Hash utilities for repartitioning data | ||
| use arrow::datatypes::DataType; | ||
| use datafusion_common::Result; | ||
| use datafusion_expr::{ColumnarValue, ScalarUDFImpl}; | ||
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| use ahash::RandomState; | ||
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| /// RandomState used for consistent hash partitioning | ||
| const REPARTITION_RANDOM_STATE: RandomState = RandomState::with_seeds(0, 0, 0, 0); | ||
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| /// Internal hash function used for repartitioning inputs. | ||
| /// This is used for partitioned HashJoinExec and partitioned GroupByExec. | ||
| /// Currently we use AHash with fixed seeds, but this is subject to change. | ||
| /// We make no promises about stability of this function across versions. | ||
| /// Currently this is *not* stable across machines since AHash is not stable across platforms, | ||
| /// thus this should only be used in a single node context. | ||
| #[derive(Debug)] | ||
| pub(crate) struct RepartitionHash { | ||
| signature: datafusion_expr::Signature, | ||
| /// RandomState for consistent hashing - using the same seed as hash joins | ||
| random_state: RandomState, | ||
| } | ||
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| impl PartialEq for RepartitionHash { | ||
| fn eq(&self, other: &Self) -> bool { | ||
| // RandomState doesn't implement PartialEq, so we just compare signatures | ||
| self.signature == other.signature | ||
| } | ||
| } | ||
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| impl Eq for RepartitionHash {} | ||
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| impl std::hash::Hash for RepartitionHash { | ||
| fn hash<H: std::hash::Hasher>(&self, state: &mut H) { | ||
| // Only hash the signature since RandomState doesn't implement Hash | ||
| self.signature.hash(state); | ||
| } | ||
| } | ||
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| impl RepartitionHash { | ||
| /// Create a new RepartitionHash | ||
| pub(crate) fn new() -> Self { | ||
| Self { | ||
| signature: datafusion_expr::Signature::one_of( | ||
| vec![datafusion_expr::TypeSignature::VariadicAny], | ||
| datafusion_expr::Volatility::Immutable, | ||
| ), | ||
| random_state: REPARTITION_RANDOM_STATE, | ||
| } | ||
| } | ||
| } | ||
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| impl ScalarUDFImpl for RepartitionHash { | ||
| fn as_any(&self) -> &dyn std::any::Any { | ||
| self | ||
| } | ||
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| fn name(&self) -> &str { | ||
| "repartition_hash" | ||
| } | ||
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| fn signature(&self) -> &datafusion_expr::Signature { | ||
| &self.signature | ||
| } | ||
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| fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> { | ||
| // Always return UInt64Array regardless of input types | ||
| Ok(DataType::UInt64) | ||
| } | ||
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| fn invoke_with_args( | ||
| &self, | ||
| args: datafusion_expr::ScalarFunctionArgs, | ||
| ) -> Result<ColumnarValue> { | ||
| use arrow::array::{Array, UInt64Array}; | ||
| use datafusion_common::hash_utils::create_hashes; | ||
| use std::sync::Arc; | ||
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| if args.args.is_empty() { | ||
| return datafusion_common::plan_err!("repartition_hash requires at least one argument"); | ||
| } | ||
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| // Convert all arguments to arrays | ||
| let arrays = ColumnarValue::values_to_arrays(&args.args)?; | ||
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| // Check that all arrays have the same length | ||
|
There was a problem hiding this comment. I think |
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| let array_len = arrays[0].len(); | ||
| for (i, array) in arrays.iter().enumerate() { | ||
| if array.len() != array_len { | ||
| return datafusion_common::plan_err!( | ||
| "All input arrays must have the same length. Array 0 has length {}, but array {} has length {}", | ||
| array_len, i, array.len() | ||
| ); | ||
| } | ||
| } | ||
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| // If no rows, return an empty UInt64Array | ||
| if array_len == 0 { | ||
| return Ok(ColumnarValue::Array(Arc::new(UInt64Array::from( | ||
| Vec::<u64>::new(), | ||
| )))); | ||
| } | ||
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| // Create hash buffer and compute hashes using DataFusion's internal algorithm | ||
| let mut hashes_buffer = vec![0u64; array_len]; | ||
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There was a problem hiding this comment. I will flag that previously the same vec was re-used with a capacity bump followed by a clear. Now we're creating a new one for each batch. It's some more allocations, but we're also pre-allocating the entire size, etc. I'm not sure if this will be measurable or not. There was a problem hiding this comment. I think we should maintain that behavior if possible. If the primary goal here is to encapsulate re-partitioning logic in this module, can we add a function for this? Something like: /// Calculates the partition used by the repartition operator for each row. All arrays should have the same length.
fn compute_partition_indices(buf: &mut Vec<u64>, arrays: &[ArrayRef], num_partitions: usize) -> Result<()> {
buf.resize(arrays[0].len(), 0);
create_hashes(arrays, REPARTITION_RANDOM_STATE, buf);
buf.iter_mut().for_each(|hash| *hash %= num_partitions as u64);
}That way the repartitioning code can simply utilize this with the once allocated vector. But the dynamic filter can use the UDF, which still utilizes this under the hood There was a problem hiding this comment. Yes agreed, I think that's better. I'll cook something up. |
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| create_hashes(&arrays, &self.random_state, &mut hashes_buffer)?; | ||
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| // Return the hash values as a UInt64Array | ||
| Ok(ColumnarValue::Array(Arc::new(UInt64Array::from( | ||
| hashes_buffer, | ||
| )))) | ||
| } | ||
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| fn documentation(&self) -> Option<&datafusion_expr::Documentation> { | ||
| None | ||
| } | ||
| } | ||
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