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perf: optimize shuffle writer with buffered I/O and fix file size bug #1386

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Merged
andygrove merged 1 commit into from
Jan 17, 2026
Merged

perf: optimize shuffle writer with buffered I/O and fix file size bug #1386

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8 changes: 5 additions & 3 deletions ballista/core/src/execution_plans/shuffle_writer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@ use std::fmt::Debug;
use std::fs;
use std::fs::File;
use std::future::Future;
use std::io::BufWriter;
use std::iter::Iterator;
use std::path::PathBuf;
use std::sync::Arc;
Expand Down Expand Up @@ -105,7 +106,7 @@ impl std::fmt::Display for ShuffleWriterExec {
pub struct WriteTracker {
pub num_batches: usize,
pub num_rows: usize,
pub writer: StreamWriter<File>,
pub writer: StreamWriter<BufWriter<File>>,
pub path: PathBuf,
}

Expand Down Expand Up @@ -295,7 +296,8 @@ impl ShuffleWriterExec {
CompressionType::LZ4_FRAME,
))?;

let file = File::create(path.clone())?;
let file =
BufWriter::new(File::create(path.clone())?);
let mut writer =
StreamWriter::try_new_with_options(
file,
Expand Down Expand Up @@ -323,8 +325,8 @@ impl ShuffleWriterExec {

for (i, w) in writers.iter_mut().enumerate() {
if let Some(w) = w {
let num_bytes = fs::metadata(&w.path)?.len();
w.writer.finish()?;
let num_bytes = fs::metadata(&w.path)?.len();
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@milenkovicm milenkovicm Jan 17, 2026

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took me a moment to understand whats changed

debug!(
"Finished writing shuffle partition {} at {:?}. Batches: {}. Rows: {}. Bytes: {}.",
i, w.path, w.num_batches, w.num_rows, num_bytes
Expand Down
5 changes: 3 additions & 2 deletions ballista/core/src/utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@ use datafusion::physical_plan::metrics::MetricsSet;
use datafusion::physical_plan::{ExecutionPlan, RecordBatchStream, metrics};
use futures::StreamExt;
use log::error;
use std::io::BufWriter;
use std::sync::Arc;
use std::time::{Duration, SystemTime, UNIX_EPOCH};
use std::{fs::File, pin::Pin};
Expand Down Expand Up @@ -148,10 +149,10 @@ pub async fn write_stream_to_disk(
path: &str,
disk_write_metric: &metrics::Time,
) -> Result<PartitionStats> {
let file = File::create(path).map_err(|e| {
let file = BufWriter::new(File::create(path).map_err(|e| {
error!("Failed to create partition file at {path}: {e:?}");
BallistaError::IoError(e)
})?;
})?);

let mut num_rows = 0;
let mut num_batches = 0;
Expand Down