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Clarify CRT minimumPartSizeInBytes Javadoc for downloads and default sizes #7484

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adev-code merged 2 commits into from
Oct 28, 2026
Merged

Clarify CRT minimumPartSizeInBytes Javadoc for downloads and default sizes #7484

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0e0cead
Clarify CRT part size Javadoc: applies to downloads, update defaults
adev-code Oct 25, 2026
33b7fff
Mention copies in CRT minimumPartSizeInBytes Javadoc, remove changelog
adev-code Oct 27, 2026
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6 changes: 6 additions & 0 deletions .changes/next-release/documentation-AWSCRTbasedS3Client-b228275.json
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@@ -0,0 +1,6 @@
{
"type": "documentation",
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"category": "AWS CRT-based S3 Client",
"description": "Clarified in the Javadoc that minimumPartSizeInBytes applies to downloads as well as uploads, and updated the default part size and initial read buffer size descriptions. See [#5158](https://github.com/aws/aws-sdk-java-v2/issues/5158).",
"contributor": "adev-code"
}
19 changes: 11 additions & 8 deletions services/s3/src/main/java/software/amazon/awssdk/services/s3/S3CrtAsyncClientBuilder.java
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Expand Up @@ -110,18 +110,21 @@ default S3CrtAsyncClientBuilder credentialsProvider(IdentityProvider<? extends A
S3CrtAsyncClientBuilder region(Region region);

/**
* Sets the minimum part size for transfer parts. Decreasing the minimum part size causes multipart transfer to be split into
* a larger number of smaller parts. Setting this value too low has a negative effect on transfer speeds, causing extra
* latency and network communication for each part.
* Sets the minimum part size for transfer parts. This applies to both uploads and downloads: uploads are sent as multipart
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* upload parts of this size, and downloads are fetched in parts of this size using ranged GET requests. Decreasing the
* minimum part size causes a transfer to be split into a larger number of smaller parts. Setting this value too low has a
* negative effect on transfer speeds, causing extra latency and network communication for each part.
*
* <p>
* By default, it is 8MB. See <a href="https://docs.aws.amazon.com/AmazonS3/latest/userguide/qfacts.html">Amazon S3 multipart
* upload limits</a> for guidance.
* If not set, uploads use a part size of 8MB, and downloads use a part size that the AWS CRT chooses based on the
* {@link #maxNativeMemoryLimitInBytes(Long)} and {@link #targetThroughputInGbps(Double)} settings. See
* <a href="https://docs.aws.amazon.com/AmazonS3/latest/userguide/qfacts.html">Amazon S3 multipart upload limits</a> for
* guidance on upload part sizes.
*
* @param uploadPartSize The minimum part size for transfer parts.
* @param partSizeInBytes The minimum part size for transfer parts.
* @return this builder for method chaining.
*/
S3CrtAsyncClientBuilder minimumPartSizeInBytes(Long uploadPartSize);
S3CrtAsyncClientBuilder minimumPartSizeInBytes(Long partSizeInBytes);

/**
* The amount of native memory that CRT is allowed to use when making requests to S3.
Expand Down Expand Up @@ -223,7 +226,7 @@ S3CrtAsyncClientBuilder maxNativeMemoryLimitInBytes(Long maxNativeMemoryLimitInB
* parts. Maintain a smaller window to limit the amount of data buffered in memory.
*
* <p>
* By default, it is equal to the resolved part size * 10
* By default, it is 10 times the {@link #minimumPartSizeInBytes(Long)} value, or 80MB if no part size is set.
*
* @param initialReadBufferSizeInBytes the initial read buffer size
* @return this builder for method chaining.
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