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stream: limit iter from sync iterable batches#63324

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trivikr:stream-iter-from-iterable-batching
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stream: limit iter from sync iterable batches#63324
trivikr wants to merge 2 commits into
nodejs:mainfrom
trivikr:stream-iter-from-iterable-batching

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@trivikr trivikr commented May 15, 2026

Description

This updates stream/iter normalization to use bounded batches for sync
iterable input.

from() no longer batches sync iterables into one unbounded batch. Instead, it
flushes at FROM_BATCH_SIZE, improving first-batch latency and bounding peak
batch memory. fromSync() now also coalesces plain Uint8Array values from
sync iterables into bounded batches, allowing pipeToSync() to use writevSync
for those sources.

Benchmarks

Results showed statistically significant first-batch latency improvements for
from(syncIterable):

  • +3.19% for 256 chunks
  • +5.01% for 4096 chunks
  • +2.80% for 16384 chunks

The benchmark also showed a +6.91% writevSync improvement for the 256 chunk
case. The 4096 chunk writev result was not statistically significant.

                                                                                         confidence improvement accuracy (*)   (**)  (***)
streams/iter-from-batching.js n=100 chunkSize=16 chunks=256 method='from-sync-writev'           ***      6.91 %       ±1.99% ±2.65% ±3.46%
streams/iter-from-batching.js n=100 chunkSize=16 chunks=4096 method='from-sync-writev'                  -2.63 %       ±3.60% ±4.84% ±6.41%
streams/iter-from-batching.js n=1000 chunkSize=16 chunks=16384 method='from-first-batch'        ***      2.80 %       ±1.39% ±1.86% ±2.44%
streams/iter-from-batching.js n=1000 chunkSize=16 chunks=256 method='from-first-batch'          ***      3.19 %       ±1.27% ±1.68% ±2.19%
streams/iter-from-batching.js n=1000 chunkSize=16 chunks=4096 method='from-first-batch'         ***      5.01 %       ±2.60% ±3.48% ±4.59%

Assisted-by: openai:gpt-5.5

trivikr added 2 commits May 14, 2026 23:11
@trivikr
stream: limit iter from sync iterable batches
c2f0e3f 
Bound sync iterable normalization in from() and fromSync() to
FROM_BATCH_SIZE. This avoids unbounded batches for from() sync
iterable fallbacks and lets fromSync() coalesce plain Uint8Array
values for writev paths.

Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
Assisted-by: openai:gpt-5.5
@trivikr
benchmark: add stream/iter from batching benchmark
d08b083
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nodejs-github-bot commented May 15, 2026

Review requested:

  • @nodejs/performance
  • @nodejs/streams

@nodejs-github-bot nodejs-github-bot added needs-ci PRs that need a full CI run. stream Issues and PRs related to the stream subsystem. labels May 15, 2026
@trivikr trivikr self-assigned this May 15, 2026
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codecov Bot commented May 15, 2026 •
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Codecov Report

❌ Patch coverage is 57.89474% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.02%. Comparing base (2edd842) to head (d08b083).
⚠️ Report is 15 commits behind head on main.

Files with missing lines Patch % Lines
lib/internal/streams/iter/from.js 57.89% 24 Missing ⚠️
Additional details and impacted files 
@@            Coverage Diff             @@
##             main   #63324      +/-   ##
==========================================
- Coverage   90.04%   90.02%   -0.03%     
==========================================
  Files         714      714              
  Lines      225338   225377      +39     
  Branches    42598    42610      +12     
==========================================
- Hits       202897   202886      -11     
- Misses      14236    14267      +31     
- Partials     8205     8224      +19
Files with missing lines Coverage Δ
lib/internal/streams/iter/from.js 86.05% <57.89%> (-2.77%) ⬇️

... and 29 files with indirect coverage changes

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@trivikr trivikr added request-ci Add this label to start a Jenkins CI on a PR. author ready PRs that have at least one approval, no pending requests for changes, and a CI started. labels May 15, 2026
@github-actions github-actions Bot removed the request-ci Add this label to start a Jenkins CI on a PR. label May 15, 2026
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nodejs-github-bot commented May 15, 2026

CI: https://ci.nodejs.org/job/node-test-pull-request/73476/

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@jasnell jasnell jasnell approved these changes

@Ethan-Arrowood Ethan-Arrowood Ethan-Arrowood approved these changes

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