rluvaton commented on code in PR #15700: URL: https://github.com/apache/datafusion/pull/15700#discussion_r2213137522
########## datafusion/physical-plan/src/sorts/multi_level_merge.rs: ########## @@ -0,0 +1,342 @@ +// 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. + +//! Create a stream that do a multi level merge stream + +use crate::metrics::BaselineMetrics; +use crate::{EmptyRecordBatchStream, SpillManager}; +use arrow::array::RecordBatch; +use std::fmt::{Debug, Formatter}; +use std::mem; +use std::pin::Pin; +use std::sync::Arc; +use std::task::{Context, Poll}; + +use arrow::datatypes::SchemaRef; +use datafusion_common::Result; +use datafusion_execution::memory_pool::{ + MemoryConsumer, MemoryPool, MemoryReservation, UnboundedMemoryPool, +}; + +use crate::sorts::streaming_merge::{SortedSpillFile, StreamingMergeBuilder}; +use crate::stream::RecordBatchStreamAdapter; +use datafusion_execution::{RecordBatchStream, SendableRecordBatchStream}; +use datafusion_physical_expr_common::sort_expr::LexOrdering; +use futures::TryStreamExt; +use futures::{Stream, StreamExt}; + +/// Merges a stream of sorted cursors and record batches into a single sorted stream +pub(crate) struct MultiLevelMergeBuilder { + spill_manager: SpillManager, + schema: SchemaRef, + sorted_spill_files: Vec<SortedSpillFile>, + sorted_streams: Vec<SendableRecordBatchStream>, + expr: LexOrdering, + metrics: BaselineMetrics, + batch_size: usize, + reservation: MemoryReservation, + fetch: Option<usize>, + enable_round_robin_tie_breaker: bool, + + // This is for avoiding double reservation of memory from our side and the sort preserving merge stream + // side. + // and doing a lot of code changes to avoid accounting for the memory used by the streams + unbounded_memory_pool: Arc<dyn MemoryPool>, +} + +impl Debug for MultiLevelMergeBuilder { + fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result { + write!(f, "MultiLevelMergeBuilder") + } +} + +impl MultiLevelMergeBuilder { + #[allow(clippy::too_many_arguments)] + pub(crate) fn new( + spill_manager: SpillManager, + schema: SchemaRef, + sorted_spill_files: Vec<SortedSpillFile>, + sorted_streams: Vec<SendableRecordBatchStream>, + expr: LexOrdering, + metrics: BaselineMetrics, + batch_size: usize, + reservation: MemoryReservation, + fetch: Option<usize>, + enable_round_robin_tie_breaker: bool, + ) -> Self { + Self { + spill_manager, + schema, + sorted_spill_files, + sorted_streams, + expr, + metrics, + batch_size, + reservation, + enable_round_robin_tie_breaker, + fetch, + unbounded_memory_pool: Arc::new(UnboundedMemoryPool::default()), + } + } + + pub(crate) fn create_spillable_merge_stream(self) -> SendableRecordBatchStream { + Box::pin(RecordBatchStreamAdapter::new( + Arc::clone(&self.schema), + futures::stream::once(self.create_stream()).try_flatten(), + )) + } + + async fn create_stream(mut self) -> Result<SendableRecordBatchStream> { + loop { + // Hold this for the lifetime of the stream + let mut current_memory_reservation = self.reservation.new_empty(); + let mut stream = + self.create_sorted_stream(&mut current_memory_reservation)?; + + // TODO - add a threshold for number of files to disk even if empty and reading from disk so + // we can avoid the memory reservation + + // If no spill files are left, we can return the stream as this is the last sorted run + // TODO - We can write to disk before reading it back to avoid having multiple streams in memory + if self.sorted_spill_files.is_empty() { + // Attach the memory reservation to the stream as we are done with it + // but because we replaced the memory reservation of the merge stream, we must hold + // this to make sure we have enough memory + return Ok(Box::pin(StreamAttachedReservation::new( + stream, + current_memory_reservation, + ))); + } Review Comment: Never mind, this can't happen as we take the largest record batch * merge degree -- This is an automated message from the Apache Git Service. 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