fix(storage): optimize gRPC writer with zero-copy and lazy allocation by cpriti-os · Pull Request #13481 · googleapis/google-cloud-go

cpriti-os · 2025-12-15T12:22:17Z

This change eliminates unnecessary double-buffering in the gRPC writer,
reducing memory usage by up to 50% for Parallel Composite Uploads (PCU)
and large single-shot uploads.

Key changes:

Implements a Zero-Copy path in gRPCWriter: if in one-shot mode, the writer now
passes the user's memory directly to the gRPC transport layer instead
of copying it into an internal buffer.
Implements Lazy Allocation: The internal buffer (w.buf) is now
initialized to nil and is only allocated if the "Slow Path" (buffering)
is triggered. This allows purely zero-copy workloads to run with
near-zero overhead.
Adds chunkSize to gRPCWriter to support logic when w.buf is nil.
Adds comprehensive tests verifying memory addresses to ensure the
optimization is active and strictly correct during retries.

gemini-code-assist · 2025-12-15T12:22:33Z

Summary of Changes

Hello @cpriti-os, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly optimizes the gRPC writer by eliminating unnecessary double-buffering, which can reduce memory usage by up to 50% for large file uploads and parallel composite uploads. The core improvements involve introducing a zero-copy path for efficient data transfer and implementing lazy allocation for the internal write buffer, ensuring that memory is only used when strictly necessary.

Highlights

Zero-Copy Path: Implemented a zero-copy mechanism in gRPCWriter that directly passes user memory to the gRPC transport layer for large inputs (>= chunk size) or one-shot uploads, avoiding internal buffer copies.
Lazy Buffer Allocation: The internal buffer (w.buf) is now initialized to nil and only allocated if buffering is required, reducing overhead for purely zero-copy workloads.
chunkSize Field: Added chunkSize to the gRPCWriter struct to support the new zero-copy and lazy allocation logic.
Comprehensive Testing: New tests were added to verify the zero-copy optimization, including scenarios for one-shot uploads, buffering fallback, and correct memory address handling during retries.

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gemini-code-assist

Code Review

This pull request introduces a significant optimization to the gRPC writer by implementing a zero-copy path and lazy allocation of the internal buffer. The changes are well-structured, and the logic for handling zero-copy writes, including partial sends and retries, appears robust. The addition of comprehensive tests that verify memory addresses is excellent and provides strong confidence in the correctness of the optimization. I've found one potential issue regarding integer overflow on 32-bit systems, for which I've left a specific comment. Overall, this is a great improvement for memory efficiency.

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

tritone

Great optimization!

Looks like there are some failing emulator tests involving progress func callbacks, race detector issues, and a deadlock. LMK if you have any questions about any of these. Probably you'll need to work on thread safety between the buffer alloc and the pipelined sends.

In addition we'd probably want to think about how to message this -- does this change how the writer "should" be used for gRPC? Do we want to suggest buffer pooling in the user application?

Finally, it'd be useful to get a pprof CPU/memory profile for before/after on this.

cpriti-os · 2026-02-25T11:33:11Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a zero-copy optimization and lazy buffer allocation for the gRPC writer, which is a great improvement for memory efficiency. The implementation looks solid, especially the retry logic in the zero-copy path. I've found a couple of areas for improvement: one is a potential memory leak issue in the new zero-copy logic, and the other is an issue in the new tests that causes them to not correctly verify the new behavior. My detailed comments are below.

krishnamd-jkp

initial review

krishnamd-jkp · 2026-02-27T10:59:19Z

Approving based on the changes. Just check if the synchronous nature of the single shot write does not qualify for a breaking change.

tritone

Generally looks good, a few questions

PR created by the Librarian CLI to initialize a release. Merging this PR will auto trigger a release. Librarian Version: v0.8.3 Language Image: us-central1-docker.pkg.dev/cloud-sdk-librarian-prod/images-prod/librarian-go@sha256:19bb93e8f1f916c61b597db2bad65dc432f79baaabb210499d7d0e4ad1dffe29 <details><summary>storage: v1.61.0</summary> ## [v1.61.0](storage/v1.60.0...storage/v1.61.0) (2026-03-10) ### Features * add bucket encryption enforcement configuration (#13874) ([245c8d7](245c8d76)) * add multistream options to MRD (#13758) ([4557675](4557675e)) * add a DeleteFolderRecursive API definition (PiperOrigin-RevId: 866471251) ([6f31019](6f310199)) * add multistream support to MRD (#13792) ([ffa7268](ffa7268c)) ### Bug Fixes * Fix TM download dir corner case (#14142) ([87cdcc9](87cdcc9f)) * Omit auto checksum in final request when MD5 is given (#14024) ([d404777](d4047774)) * optimize gRPC writer with zero-copy and lazy allocation (#13481) ([df64147](df641476)) </details>

fix(storage): optimize gRPC writer with zero-copy and lazy allocation

bbb38ea

cpriti-os requested review from a team December 15, 2025 12:22

cpriti-os requested a review from a team as a code owner December 15, 2025 12:22

product-auto-label Bot added the api: storage Issues related to the Cloud Storage API. label Dec 15, 2025

gemini-code-assist Bot reviewed Dec 15, 2025

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Comment thread storage/grpc_writer.go Outdated

cpriti-os and others added 2 commits December 15, 2025 17:59

Apply suggestion from @gemini-code-assist[bot]

0b8e9c3

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

fix imports

b049949

tritone reviewed Dec 15, 2025

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cpriti-os added 2 commits December 31, 2025 06:18

fix some emulator tests

541037e

fix reuse buffer for grpc writer.

12dcec2

cpriti-os requested review from a team as code owners February 25, 2026 09:19

use zero copy only for chunk size 0 to avoid performane regressions

45ed647

gemini-code-assist Bot reviewed Feb 25, 2026

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Comment thread storage/grpc_writer.go Outdated

Comment thread storage/grpc_writer_test.go Outdated

fix vet

8eaadfd

cpriti-os requested review from krishnamd-jkp and tritone February 25, 2026 12:00

krishnamd-jkp reviewed Feb 25, 2026

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Comment thread storage/grpc_writer.go Outdated

Comment thread storage/grpc_writer.go Outdated

Comment thread storage/grpc_writer.go Outdated

Comment thread storage/grpc_writer.go Outdated

Comment thread storage/grpc_writer.go Outdated

Comment thread storage/grpc_writer.go

resolve comments

fdc6294

cpriti-os requested a review from krishnamd-jkp February 25, 2026 16:11

cpriti-os added 2 commits February 26, 2026 04:24

resolve comments

2d9aa90

simplify

ba4c8aa

krishnamd-jkp reviewed Feb 26, 2026

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Comment thread storage/grpc_writer_test.go Outdated

fix test

e995d1c

cpriti-os requested a review from krishnamd-jkp February 27, 2026 07:50

krishnamd-jkp approved these changes Feb 27, 2026

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cpriti-os added the kokoro:force-run Add this label to force Kokoro to re-run the tests. label Mar 2, 2026

kokoro-team removed the kokoro:force-run Add this label to force Kokoro to re-run the tests. label Mar 2, 2026

Merge branch 'googleapis:main' into zero-grpc

a993296

tritone reviewed Mar 3, 2026

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Comment thread storage/grpc_writer.go Outdated

Comment thread storage/grpc_writer.go Outdated

Comment thread storage/grpc_writer_test.go Outdated

resolve some comments

fa45c32

tritone approved these changes Mar 3, 2026

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cpriti-os added 2 commits March 5, 2026 12:04

add more test cases

cdc51f8

comments

58c2694

cpriti-os merged commit df64147 into googleapis:main Mar 5, 2026
10 checks passed

cpriti-os deleted the zero-grpc branch March 6, 2026 11:25

krishnamd-jkp mentioned this pull request Mar 10, 2026

chore: librarian release pull request: 20260310T073310Z #14148

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gemini-code-assist Bot commented Dec 15, 2025

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cpriti-os commented Feb 25, 2026

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krishnamd-jkp commented Feb 27, 2026

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cpriti-os commented Dec 15, 2025 •

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