Sync: upload/delete S3 files concurrently, not one directory call#3650
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S3 sync is network-bound, not CPU-bound, so uploads and deletes now run in parallel per-file/per-batch (configurable via DOCS_SYNC_UPLOAD_CONCURRENCY and DOCS_SYNC_DELETE_CONCURRENCY) instead of copying every file to a temp directory and issuing a single directory upload sized to CPU count. Failures are now reported per-file/per-batch via the diagnostics collector instead of aborting the whole sync, and Apply returns false if any file failed. The S3 client also configures SDK-level retry (standard mode) to absorb throttling under the higher concurrency. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
…sync-w/o-bound-not-cpu-bound-opportunity-most-systems-ca
Mpdreamz
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Jul 13, 2026
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LGTM, let's make sure we isolate this in a release (EMG a release only containing this change before releasing.
That way we can isolate the change and see it on edge and staging and rollback roll forward.
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Why
S3 sync during deploy is network-bound, not CPU-bound: the old apply strategy copied every file to a temp directory and issued a single
TransferUtilityUploadDirectoryRequest, whose concurrency was tied to CPU count viaTransferUtilityConfig.ConcurrentServiceRequests. For a docs-site sync with many small files, that under-utilizes available network concurrency and wastes a full local read+write pass per file just to stage a directory that already matched the S3 key layout. A single failed upload/delete could also abort the whole batch.What
Uploads and deletes now run per-file/per-batch in parallel via
Parallel.ForEachAsync, with concurrency configurable throughDOCS_SYNC_UPLOAD_CONCURRENCY(default 32, max 128) andDOCS_SYNC_DELETE_CONCURRENCY(default 4, max 16). Each file is uploaded directly from its original path with an explicit S3 key — no temp-directory staging. Failures are now isolated and reported per-file/per-batch through the diagnostics collector instead of aborting the whole sync, andAwsS3SyncApplyStrategy.Applyreturnsfalseif any file failed (previously the caller always reported success). The defaultAmazonS3Clientalso now configures SDK-level retry (RequestRetryMode.Standard,MaxErrorRetry = 5) to absorb throttling under the higher concurrency.Test plan
dotnet buildsucceedsDocsSyncTests,IncrementalDeployRoundTripTests), including new tests covering delete-batch chunking and upload-failure propagation