Parallel composite uploads

Note: If you interact with Cloud Storage via the XML API, consider using XML API multipart uploads instead of parallel composite uploads: XML API multipart uploads support a greater number of parts than compose operations, have less potential for early deletion fees, and don't require Delete requests to remove the source parts once the final object is assembled.

One strategy for uploading large files is called parallel composite uploads. In such an upload, a file is divided into up to 32 chunks, the chunks are uploaded in parallel to temporary objects, the final object is recreated using the temporary objects, and the temporary objects are deleted.

Parallel composite uploads can be significantly faster if network and disk speed are not limiting factors; however, the final object stored in your bucket is a composite object, which only has a crc32c hash and not an MD5 hash. As a result, you must use crcmod to perform integrity checks when downloading the object with Python applications. You should only perform parallel composite uploads if the following apply:

• You don't need the uploaded objects to have an MD5 hash.

• Any Python user, including gsutil users, who needs to download your objects has either google-crc32c or crcmod installed.

  For example, if you use Python to upload video assets that are only served by a Java application, parallel composite uploads are a good choice because there are efficient CRC32C implementations available in Java.

Warning: Parallel composite uploads involve deleting temporary objects shortly after upload. Keep in mind the following:

• Because other storage classes are subject to early deletion fees, you should always use Standard storage for temporary objects. Once the final object is composed, you can change its storage class.
• You should not use parallel composite uploads when uploading to a bucket that has a retention policy, because the temporary objects can't be deleted until they meet the retention period.
• If the bucket you upload to has default object holds enabled, you must release the hold from each temporary object before you can delete it.

How tools and APIs use parallel composite uploads

Depending on how you interact with Cloud Storage, parallel composite uploads might be managed automatically on your behalf. This section describes parallel composite upload behavior for different tools and provides information for how you can modify the behavior.

Console

The Google Cloud console does not perform parallel composite uploads.

Command line

You can configure how and when gcloud storage cp performs parallel composite uploads by modifying the following properties:

• storage/parallel_composite_upload_enabled: Property for enabling parallel composite uploads. If False, disable parallel composite uploads. If True or None, perform parallel composite uploads for objects that meet the criteria defined in the other properties. The default setting is None.

• storage/parallel_composite_upload_compatibility_check: Property for toggling safety checks. If True, gcloud storage only performs parallel composite uploads when all of the following conditions are met:

  • The storage class for the uploaded object is STANDARD.
  • The destination bucket does not have a retention policy.
  • The destination bucket does not have default object holds enabled.

  Note that in order to check these conditions, the gcloud CLI retrieves the metadata for the destination bucket as part of the upload command.

  If False, gcloud storage does not perform any checks. The default setting is True.

• storage/parallel_composite_upload_threshold: The minimum total file size for performing a parallel composite upload. The default setting is 150 MiB.

• storage/parallel_composite_upload_component_size: The maximum size for each temporary object. The property is ignored if the total file size is so large that it would require more than 32 chunks at this size.

• storage/parallel_composite_upload_component_prefix: The prefix used when naming temporary objects. This property can be set either as an absolute path or as a path relative to the final object. See the property description for more information. The default prefix is the absolute path /gcloud/tmp/parallel_composite_uploads/see_gcloud_storage_cp_help_for_details.

You can modify these properties by creating a named configuration and applying the configuration either on a per-command basis by using the --configuration project-wide flag or for all gcloud CLI commands by using the gcloud config set command.

No additional local disk space is required when using gcloud CLI to perform parallel composite uploads. If a parallel composite upload fails prior to composition, run the gcloud CLI command again to take advantage of resumable uploads for the temporary objects that failed. Any temporary objects that uploaded successfully before the failure do not get re-uploaded when you resume the upload.

Temporary objects are named in the following fashion:

TEMPORARY_PREFIX/RANDOM_VALUE_HEX_DIGEST_COMPONENT_ID

Where:

• TEMPORARY_PREFIX is controlled by the storage/parallel_composite_upload_component_prefix property.
• RANDOM_VALUE is a random numerical value.
• HEX_DIGEST is a hash derived from the name of the source resource.
• COMPONENT_ID is the sequential number of the component.

Generally, temporary objects are deleted at the end of a parallel composite upload, but to avoid leaving temporary objects around, you should check the exit status from the gcloud CLI command, and you should manually delete any temporary objects that were uploaded as part of any aborted upload.

Client libraries

Java

For more information, see the Cloud Storage Java API reference documentation.

To authenticate to Cloud Storage, set up Application Default Credentials. For more information, see Set up authentication for client libraries.

You can perform parallel composite uploads by setting AllowParallelCompositeUpload to true. For example:

import com.google.cloud.storage.transfermanager.ParallelUploadConfig;
import com.google.cloud.storage.transfermanager.TransferManager;
import com.google.cloud.storage.transfermanager.TransferManagerConfig;
import com.google.cloud.storage.transfermanager.UploadResult;
import java.io.IOException;
import java.nio.file.Path;
import java.util.List;

class AllowParallelCompositeUpload {

  public static void parallelCompositeUploadAllowed(String bucketName, List<Path> files)
      throws IOException {
    TransferManager transferManager =
        TransferManagerConfig.newBuilder()
            .setAllowParallelCompositeUpload(true)
            .build()
            .getService();
    ParallelUploadConfig parallelUploadConfig =
        ParallelUploadConfig.newBuilder().setBucketName(bucketName).build();
    List<UploadResult> results =
        transferManager.uploadFiles(files, parallelUploadConfig).getUploadResults();
    for (UploadResult result : results) {
      System.out.println(
          "Upload for "
              + result.getInput().getName()
              + " completed with status "
              + result.getStatus());
    }
  }
}

Node.js

For more information, see the Cloud Storage Node.js API reference documentation.

To authenticate to Cloud Storage, set up Application Default Credentials. For more information, see Set up authentication for client libraries.

The Node.js client library does not support parallel composite uploads. Instead, use XML API multipart uploads.

Python

For more information, see the Cloud Storage Python API reference documentation.

To authenticate to Cloud Storage, set up Application Default Credentials. For more information, see Set up authentication for client libraries.

The Python client library does not support parallel composite uploads. Instead, use XML API multipart uploads.

REST APIs

Both the JSON API and XML API support uploading object chunks in parallel and recombining them into a single object using the compose operation.

Keep the following in mind when designing code for parallel composite uploads:

• When using the compose operation, the source objects are unaffected by the composition process.

  This means that if they are meant to be temporary, you must explicitly delete them once you've successfully completed the composition, or else the source objects remain in your bucket and are billed accordingly.

• In order to protect against changes to source objects between the upload and compose requests, you should provide an expected generation number for each source.