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Upload Amazon S3 Objects Using Multipart Upload (Multipart Upload) - Introduction

You can upload a single large  S3 Object (File) in multiple smaller parts using Multipart Upload. In Multipart upload process, each part is a portion of the object's data. Each part can be uploaded independently and in any order. If transmission of any part fails, you can retransmit that part without affecting other parts. After all parts of your object are uploaded successfully, Amazon S3 then represents the data as a single object. Multipart Upload offers many benefits over simple upload, especially when object size is very large.

Using Multipart upload provides the following advantages:

  1. Restart Uploading Objects : If a part fails to upload, then you need to resend the data for that part only.
  2. Pause and Resume Upload Operation : You can pause as well as resume a part which is being uploaded with Multipart Upload.
  3. Parallel Upload : Multipart upload provides benefits of uploading object parts in parallel.
  4. You do not need to worry about the size of object as you can upload parts without knowing the size of the final object.
  5. Canceling Multipart upload will no longer be billed for any storage that was associated with the parts which have been stored.

Some facts:

  1. Maximum object size for multipart operations can be 5TB.
  2. Maximum of 10,000 numbers of parts can be possible per upload.
  3. Part numbers: Each part has a part number. It can lie between 1 to 10,000 (inclusive).
  4. Part Size: Each Part size can lie between 5 MB to 5GB other than the last part. Last part can be less than 5MB.
  5. Maximum number of parts returned for a list parts request is 1000.
  6. Maximum number of multipart uploads returned in a list multipart uploads request is 1000.

Amazon S3 Multipart Upload - using Amazon S3 REST API

To start the process, you first need to initiate multipart upload. Second Upload Parts and Third (Final One) Merging all parts to complete the upload. Parts are concatenated in ascending order of part number by Amazon S3. Complete Multipart Upload (Merging All Parts) request needs list of parts with its part number as well as ETag value of each part, returned when part was uploaded.
A. Initiate Multipart Upload

First you can initiate Multipart Upload. For this you can send a POST request. Amazon S3 responds you with a unique Identifier as Upload ID. This Upload ID is used in each operation like upload parts, list the parts, complete an upload or abort an upload.

Syntax:


POST / ObjectName?uploads HTTP/1.1
Host: BucketName .s3.amazonaws.com
Date: date
Authorization: signatureValue
 

B.1 Upload Part

You need to make a PUT request to upload a part in Multipart upload. The request includes the upload ID that you get in response to your Initiate Multipart upload request. It also includes Part number. A part number can be any number from 1 to 10,000, inclusive. A part number uniquely identifies a part and also defines its position within the object being created.

Syntax:


PUT / ObjectName ?partNumber= PartNumber &uploadId= UploadId HTTP/1.1
Host: BucketName .s3.amazonaws.com
Date: date
Content-Length: Size
Authorization: signatureValue
 

B.2 Upload Part - Copy

For Multipart Copy operation, the following PUT request uploads a part in a multipart upload. The request specifies a byte range from an existing object as the source of this upload. The request includes the upload ID that you get in response to your Initiate Multipart Upload request.

Syntax:


PUT / ObjectName ?partNumber= PartNumber &uploadId= UploadId HTTP/1.1
Host: BucketName .s3.amazonaws.com
x-amz-copy-source:/ source_bucket / sourceObject
x-amz-copy-source-range:bytes= first-last
x-amz-copy-source-if-match: etag
x-amz-copy-source-if-none-match: etag
x-amz-copy-source-if-unmodified-since: time_stamp
x-amz-copy-source-if-modified-since: time_stamp
Date: date
Authorization: Signature
 

C. Complete Multipart Upload

After successfully uploading all relevant parts of an upload, you can send a POST request to complete the Multipart upload operation. Upon receiving this request, Amazon S3 concatenates all the parts in ascending order by part number to create a final object. For this, you must provide the parts list. You must ensure that the parts list is complete. For each part in the list, you must provide the part number and the Etag header value, returned after that part was uploaded.

Syntax:


POST / ObjectName ?uploadId= UploadId HTTP/1.1
Host: BucketName .s3.amazonaws.com
Date: Date
Content-Length: Size
Authorization: Signature
<CompleteMultipartUpload>
<Part>
<PartNumber> PartNumber </PartNumber>
<ETag> ETag </ETag>
</Part>
...
</CompleteMultipartUpload>
 

D. Abort Multipart Upload:

If some parts are uploaded and after that you want to cancel the upload process, you need to Abort Multipart Upload. After a multipart upload is aborted, no additional parts can be uploaded using that upload ID. The storage consumed by any previously uploaded parts will be freed. However, if any part uploads are currently in progress, those part uploads might or might not succeed. As a result, it might be necessary to abort a given multipart upload multiple times in order to completely free all storage consumed by all parts.

Syntax:


DELETE / ObjectName ?uploadId= UploadId HTTP/1.1
Host: BucketName .s3.amazonaws.com
Date: date
Authorization: Signature
 

E. List Parts:

List Parts operation lists the parts that have been uploaded for a specific Multipart upload.
This operation must include the upload ID. This request returns a maximum of 1,000 uploaded parts. The default number of parts returned is 1,000 parts. You can restrict the number of parts returned by specifying the max-parts request parameter. If your multipart upload consists of more than 1,000 parts, the response returns an IsTruncated field with the value of true, and a NextPartNumberMarker element. In subsequent List Parts requests, you can include the part-number-marker query string parameter and set its value to the NextPartNumberMarker field value from the previous response.

Syntax:


GET / ObjectName ?uploadId= UploadId HTTP/1.1
Host: BucketName .s3.amazonaws.com
Date: date
Authorization: Signature
 

How to perform operations with S3 Multipart Upload
  • Using REST S3 API
    You can perform above Multipart Uplopad related operations by using Amazon S3 supported REST API in your application code. In this documentation we talk about REST APIs only. To get SOAP API you can refer Amazon S3 documentation.
  • Using Bucket Explorer
    You can perform the same Multipart Upload related operations using Bucket Explorer by mouse clicks without writing a single line of code.

You can perform the following S3 Multipart Upload operations

  1. Multipart Upload : This allows you to upload a single object as a set of parts. In upload process, each part is a portion of the object's data, and each part can be uploaded independently. Check the link to get more details about Multipart Upload - Upload big files in parts using Amazon REST API as well as using Bucket Explorer.
  2. Multipart Download : Object can be downloaded in parts. (Bucket Explorer's Exclusive feature) It's not available in S3 API. This allows you to download a single object as a set of parts. In download process, each part is a portion of the object's data, and each part can be downloaded independently. Check the link to get more details about Multipart Download - Download big files in parts using Bucket Explorer.
  3. Multipart Copy-Move : This allows you to copy a single object as a set of parts. In Copy process, each part is a portion of the object's data, and each part can be copied independently. Check the link to get more details about Multipart Copy - Copy big files in parts using Amazon REST API as well as using Bucket Explorer.
  4. Resume Upload, Copy & Move : It allows you to resume the interrupted Multipart Upload, Copy and Move process. It may occur either when your connection has been terminated with Amazon or you have closed the Multipart process in between competition of process. Check the link to get more details about Resume Multipart - Resume Upload, Copy & Move using Amazon REST API as well as using Bucket Explorer.
  5. Set the size of a part using Bucket Explorer