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Performance tuning for uploads and downloads with Java

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When an application transfers data using the Azure Storage client library for Java, there are several factors that can affect speed, memory usage, and even the success or failure of the request. To maximize performance and reliability for data transfers, it's important to be proactive in configuring client library transfer options based on the environment your app runs in.

This article walks through several considerations for tuning data transfer options. When properly tuned, the client library can efficiently distribute data across multiple requests, which can result in improved operation speed, memory usage, and network stability.

Performance tuning for uploads

Properly tuning data transfer options is key to reliable performance for uploads. Storage transfers are partitioned into several subtransfers based on the values of these arguments. The maximum supported transfer size varies by operation and service version, so be sure to check the documentation to determine the limits. For more information on transfer size limits for Blob storage, see Scale targets for Blob storage.

Set transfer options for uploads

You can configure the values in ParallelTransferOptions to improve performance for data transfer operations. The following values can be tuned for uploads based on the needs of your app:

  • maxSingleUploadSize: The maximum blob size in bytes for a single request upload.
  • blockSize: The maximum block size to transfer for each request.
  • maxConcurrency: The maximum number of parallel requests issued at any given time as a part of a single parallel transfer.

Note

The client libraries will use defaults for each data transfer option, if not provided. These defaults are typically performant in a data center environment, but not likely to be suitable for home consumer environments. Poorly tuned data transfer options can result in excessively long operations and even request timeouts. It's best to be proactive in testing these values, and tuning them based on the needs of your application and environment.

maxSingleUploadSize

The maxSingleUploadSize value is the maximum blob size in bytes for a single request upload. This value can be set using the following method:

If the size of the data is less than or equal to maxSingleUploadSize, the blob is uploaded with a single Put Blob request. If the blob size is greater than maxSingleUploadSize, or if the blob size is unknown, the blob is uploaded in chunks using a series of Put Block calls followed by Put Block List.

It's important to note that the value you specify for blockSize does not limit the value that you define for maxSingleUploadSize. The maxSingleUploadSize argument defines a separate size limitation for a request to perform the entire operation at once, with no subtransfers. It's often the case that you want maxSingleUploadSize to be at least as large as the value you define for blockSize, if not larger. Depending on the size of the data transfer, this approach can be more performant, as the transfer is completed with a single request and avoids the overhead of multiple requests.

If you're unsure of what value is best for your situation, a safe option is to set maxSingleUploadSize to the same value used for blockSize.

blockSize

The blockSize value is the maximum length of a transfer in bytes when uploading a block blob in chunks. This value can be set using the following method:

The blockSize value is the maximum length of a transfer in bytes when uploading a block blob in chunks. As mentioned earlier, this value does not limit maxSingleUploadSize, which can be larger than blockSize.

To keep data moving efficiently, the client libraries may not always reach the blockSize value for every transfer. Depending on the operation, the maximum supported value for transfer size can vary. For more information on transfer size limits for Blob storage, see the chart in Scale targets for Blob storage.

maxConcurrency

The maxConcurrency value is the maximum number of parallel requests issued at any given time as a part of a single parallel transfer. This value can be set using the following method:

Code example

Make sure you have the following import directive to use ParallelTransferOptions for an upload:

import com.azure.storage.blob.models.*;

The following code example shows how to set values for ParallelTransferOptions and include the options as part of a BlobUploadFromFileOptions instance. If you're not uploading from a file, you can set similar options using BlobParallelUploadOptions. The values provided in this sample aren't intended to be a recommendation. To properly tune these values, you need to consider the specific needs of your app.

ParallelTransferOptions parallelTransferOptions = new ParallelTransferOptions()
        .setBlockSizeLong((long) (4 * 1024 * 1024)) // 4 MiB block size
        .setMaxConcurrency(2)
        .setMaxSingleUploadSizeLong((long) 8 * 1024 * 1024); // 8 MiB max size for single request upload

BlobUploadFromFileOptions options = new BlobUploadFromFileOptions("<localFilePath>");
options.setParallelTransferOptions(parallelTransferOptions);

Response<BlockBlobItem> blockBlob = blobClient.uploadFromFileWithResponse(options, null, null);

In this example, we set the maximum number of parallel transfer workers to 2 using the setMaxConcurrency method. We also set maxSingleUploadSize to 8 MiB using the setMaxSingleUploadSizeLong method. If the blob size is smaller than 8 MiB, only a single request is necessary to complete the upload operation. If the blob size is larger than 8 MiB, the blob is uploaded in chunks with a maximum chunk size of 4 MiB, which we set using the setBlockSizeLong method.

Performance considerations for uploads

During an upload, the Storage client libraries split a given upload stream into multiple subuploads based on the configuration options defined by ParallelTransferOptions. Each subupload has its own dedicated call to the REST operation. For a BlobClient object, this operation is Put Block. The Storage client library manages these REST operations in parallel (depending on transfer options) to complete the full upload.

Note

Block blobs have a maximum block count of 50,000 blocks. The maximum size of your block blob, then, is 50,000 times block_size.

Buffering during uploads

The Storage REST layer doesn’t support picking up a REST upload operation where you left off; individual transfers are either completed or lost. To ensure resiliency for stream uploads, the Storage client libraries buffer data for each individual REST call before starting the upload. In addition to network speed limitations, this buffering behavior is a reason to consider a smaller value for blockSize, even when uploading in sequence. Decreasing the value of blockSize decreases the maximum amount of data that is buffered on each request and each retry of a failed request. If you're experiencing frequent timeouts during data transfers of a certain size, reducing the value of blockSize reduces the buffering time, and may result in better performance.

Performance tuning for downloads

Properly tuning data transfer options is key to reliable performance for downloads. Storage transfers are partitioned into several subtransfers based on the values defined in ParallelTransferOptions.

Set transfer options for downloads

The following values can be tuned for downloads based on the needs of your app:

  • blockSize: The maximum block size to transfer for each request. You can set this value by using the setBlockSizeLong method.
  • maxConcurrency: The maximum number of parallel requests issued at any given time as a part of a single parallel transfer. You can set this value by using the setMaxConcurrency method.

Code example

Make sure you have the following import directive to use ParallelTransferOptions for a download:

import com.azure.storage.common.*;

The following code example shows how to set values for ParallelTransferOptions and include the options as part of a BlobDownloadToFileOptions instance.

ParallelTransferOptions parallelTransferOptions = new ParallelTransferOptions()
        .setBlockSizeLong((long) (4 * 1024 * 1024)) // 4 MiB block size
        .setMaxConcurrency(2);

BlobDownloadToFileOptions options = new BlobDownloadToFileOptions("<localFilePath>");
options.setParallelTransferOptions(parallelTransferOptions);

blobClient.downloadToFileWithResponse(options, null, null);

Performance considerations for downloads

During a download, the Storage client libraries split a given download request into multiple subdownloads based on the configuration options defined by ParallelTransferOptions. Each subdownload has its own dedicated call to the REST operation. Depending on transfer options, the client libraries manage these REST operations in parallel to complete the full download.

Next steps