dwsmith1983 commented on code in PR #5568:
URL: https://github.com/apache/datafusion-comet/pull/5568#discussion_r3900506060
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native/shuffle/src/writers/local/local_partition_writer.rs:
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@@ -53,6 +53,11 @@ enum DataOutput {
spill_writers: Vec<SpillWriter>,
/// Runtime used to allocate the temporary spill files.
runtime: Arc<RuntimeEnv>,
+ /// Byte buffer recycled through the short-lived per-partition
`BufBatchWriter`s.
+ /// Partitions are written strictly one at a time, so a single buffer
keeps its
+ /// grown capacity across the whole task instead of every partition
regrowing a
+ /// fresh allocation toward the write buffer size.
+ recycled_buffer: Vec<u8>,
Review Comment:
Ran it with your shape: an 8,192-row hot batch of 8 KiB Binary payloads
followed by ~500k rows of 16-byte payloads, plus reversed-order and narrow-only
controls; codec none, 2,000 partitions, max-buffer-bytes 4 MiB (about 10 spills
per run), 3 iterations after warmup, base vs head on the same build, machine,
and input seed:
| input | base avg | head avg |
|---|---|---|
| wide-then-narrow | 0.401s | 0.384s |
| narrow-then-wide | 0.421s | 0.413s |
| narrow-only | 0.398s | 0.397s |
Head is slightly faster on all three, most on the wide-then-narrow case, so
no time regression from retention. On the memory side the answer changed while
you were writing the comment: flush now shrinks the scratch back to the
configured write-buffer size, so retained capacity after the wide batch is
bounded by construction and pinned by a test rather than instrumented at
runtime, which I think lands on the "cap" option among cap/release/account.
Spilled bytes and outputs match within the run-to-run variation of the spill
trigger (Arrow's memory estimates shift block boundaries by a spill or so even
between runs of the same binary, so byte-exact cross-tree diffs are not
meaningful under forced spilling; row-level equality is pinned by the unit
tests and the digest matrix in the review above). I did not instrument peak RSS
or live reservation traces.
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