comphead commented on code in PR #1192:
URL: https://github.com/apache/datafusion-comet/pull/1192#discussion_r1901414056
##########
native/core/src/execution/shuffle/shuffle_writer.rs:
##########
@@ -1567,17 +1585,41 @@ pub fn write_ipc_compressed<W: Write + Seek>(
let mut timer = ipc_time.timer();
let start_pos = output.stream_position()?;
- // write ipc_length placeholder
- output.write_all(&[0u8; 8])?;
+ // seek past ipc_length placeholder
+ output.seek_relative(8)?;
+
+ // write number of columns because JVM side needs to know how many
addresses to allocate
+ let field_count = batch.schema().fields().len();
+ output.write_all(&field_count.to_le_bytes())?;
let output = match codec {
CompressionCodec::None => {
+ output.write_all(b"NONE")?;
let mut arrow_writer = StreamWriter::try_new(output,
&batch.schema())?;
arrow_writer.write(batch)?;
arrow_writer.finish()?;
arrow_writer.into_inner()?
}
+ CompressionCodec::Snappy => {
+ output.write_all(b"SNAP")?;
+ let mut wtr = snap::write::FrameEncoder::new(output);
+ let mut arrow_writer = StreamWriter::try_new(&mut wtr,
&batch.schema())?;
+ arrow_writer.write(batch)?;
+ arrow_writer.finish()?;
+ wtr.into_inner()
+ .map_err(|e| DataFusionError::Execution(format!("lz4
compression error: {}", e)))?
+ }
+ CompressionCodec::Lz4Frame => {
+ output.write_all(b"LZ4_")?;
+ let mut wtr = lz4_flex::frame::FrameEncoder::new(output);
+ let mut arrow_writer = StreamWriter::try_new(&mut wtr,
&batch.schema())?;
Review Comment:
yeah, thats another way to increase `batch_size` so the compression writer
will be created less often.
The test idea was to find out how expensive is the writer creation, to see
if this can be an issue.
Perhaps I can just try to create a bench and quantify it so it gives us some
ideas.
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