Put Block List

• 6/13/2018
• 12 minutes to read
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The Put Block List operation writes a blob by specifying the list of block IDs that make up the blob. In order to be written as part of a blob, a block must have been successfully written to the server in a prior Put Block operation.

You can call Put Block List to update a blob by uploading only those blocks that have changed, then committing the new and existing blocks together. You can do this by specifying whether to commit a block from the committed block list or from the uncommitted block list, or to commit the most recently uploaded version of the block, whichever list it may belong to.

Request

The Put Block List request may be constructed as follows. HTTPS is recommended. Replace myaccount with the name of your storage account:

Emulated Storage Service URI

When making a request against the emulated storage service, specify the emulator hostname and Blob service port as 127.0.0.1:10000, followed by the emulated storage account name:

Note that the storage emulator only supports blob sizes up to 2 GB.

For more information, see Using the Azure Storage Emulator for Development and Testing.

URI Parameters

The following additional parameters may be specified on the request URI.

Request Headers

The following table describes required and optional request headers.

This operation also supports the use of conditional headers to commit the block list only if a specified condition is met. For more information, see Specifying Conditional Headers for Blob Service Operations.

Request Body

In the request body, you can specify which block list the Blob service should check for the requested block. In this way you can update an existing blob by inserting, replacing, or deleting individual blocks, rather than re-uploading the entire blob. Once you've uploaded the block or blocks that have changed, you can commit a new version of the blob by committing the new blocks together with the existing blocks that you wish to keep.

To update a blob, you can specify that the service should look for a block ID in the committed block list, in the uncommitted block list, or in the uncommitted block list first and then in the committed block list. To indicate which approach to use, specify the block ID within the appropriate XML element within the request body, as follows:

• Specify the block ID within the Committed element to indicate that the Blob service should search only the committed block list for the named block. If the block is not found in the committed block list, it will not be written as part of the blob, and the Blob service will return status code 400 (Bad Request).

• Specify the block ID within the Uncommitted element to indicate that the Blob service should search only the uncommitted block list for the named block. If the block is not found in the uncommitted block list, it will not be written as part of the blob, and the Blob service will return status code 400 (Bad Request).

• Specify the block ID within the Latest element to indicate that the Blob service should first search the uncommitted block list. If the block is found in the uncommitted list, that version of the block is the latest and should be written to the blob. If the block is not found in the uncommitted list, then the service should search the committed block list for the named block and write that block to the blob if it is found.

  The request body for this version of Put Block List uses following XML format:

<?xml version="1.0" encoding="utf-8"?>  
<BlockList>  
  <Committed>first-base64-encoded-block-id</Committed>  
  <Uncommitted>second-base64-encoded-block-id</Uncommitted>  
  <Latest>third-base64-encoded-block-id</Latest>  
  ...  
</BlockList>  

Sample Request

To demonstrate Put Block List, assume you have uploaded three blocks that you now wish to commit. The following example commits a new blob by indicating that the latest version of each block listed should be used. It's not necessary to know whether these blocks have already been committed.

Request Syntax:  
PUT https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=blocklist HTTP/1.1  

Request Headers:  
x-ms-date: Wed, 31 Aug 2011 00:17:43 GMT  
x-ms-version: 2011-08-18  
Content-Type: text/plain; charset=UTF-8  
Authorization: SharedKey myaccount:DJ5QZSVONZ64vAhnN/wxcU+Pt5HQSLAiLITlAU76Lx8=  
Content-Length: 133  

Request Body:  
<?xml version="1.0" encoding="utf-8"?>  
<BlockList>  
  <Latest>AAAAAA==</Latest>  
  <Latest>AQAAAA==</Latest>  
  <Latest>AZAAAA==</Latest>  
</BlockList>  

Next, assume that you wish to update the blob. The new blob will have the following changes:

• A new block with ID ANAAAA==. This block must first be uploaded with a call to Put Block and will appear in the uncommitted block list until the call to Put Block List.

• An updated version of the block with ID AZAAAA==. This block must first be uploaded with a call to Put Block and will appear in the uncommitted block list until the call to Put Block List.

• Removal of the block with the ID AAAAAA==. Given that this block is not included in the next call to Put Block List, the block will effectively be removed from the blob.

  The following example shows the call to Put Block List that updates the blob:

Request Syntax:  
PUT https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=blocklist HTTP/1.1  

Request Headers:  
x-ms-date: Wed, 31 Aug 2009 00:17:43 GMT  
x-ms-version: 2011-08-18  
Content-Type: text/plain; charset=UTF-8  
Authorization: SharedKey myaccount:DJ5QZSVONZ64vAhnN/wxcU+Pt5HQSLAiLITlAU76Lx8=  
Content-Length: 133  

Request Body:  
<?xml version="1.0" encoding="utf-8"?>  
<BlockList>  
  <Uncommitted>ANAAAA==</Uncommitted>  
  <Committed>AQAAAA==</Committed>  
  <Uncommitted>AZAAAA==</Uncommitted>  
</BlockList>  

Response

The response includes an HTTP status code and a set of response headers.

Status Code

A successful operation returns status code 201 (Created).

For information about status codes, see Status and Error Codes.

Response Headers

The response for this operation includes the following headers. The response may also include additional standard HTTP headers. All standard headers conform to the HTTP/1.1 protocol specification.

Sample Response

Response Status:  
HTTP/1.1 201 Created  

Response Headers:  
Transfer-Encoding: chunked  
Content-MD5: oafL1+HS78x65+e39PGIIg==  
Date: Sun, 25 Sep 2011 00:17:44 GMT  
ETag: “0x8CB172A360EC34B”  
Last-Modified: Sun, 25 Sep 2011 00:17:43 GMT  
x-ms-version: 2011-08-18  
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0  

Authorization

This operation can be called by the account owner and by anyone with a Shared Access Signature that has permission to write to this blob or its container.

Remarks

The Put Block List operation enforces the order in which blocks are to be combined to create a blob.

The same block ID can be specified more than one time in the list of blocks. If a block ID is specified more than one time, it will represent the range of bytes in each of those locations in the block list for the final committed blob. If a block ID appears more than once in the list, both instances of the block ID must be specified within the same block list. In other words, both instances must be specified within the Committed element, the Uncommitted element, or the Latest element.

With Put Block List, you can modify an existing blob by inserting, updating, or deleting individual blocks, without uploading the whole blob again. You can specify block IDs from both the current committed block list and the uncommitted block list to create a new blob or update the content of an existing blob. In this way you can update a blob by specifying a few new blocks from the uncommitted block list, and the rest from the committed block list, which are already part of the existing blob.

If a block ID is specified in the Latest element, and the same block ID exists in both the committed and uncommitted block lists, Put Block List commits the block from the uncommitted block list. If the block ID exists in the committed block list but not in the uncommitted block list, then Put Block List commits the block from the committed block list.

Each block can be a different size, up to a maximum of 100 MB for version 2016-05-31 and later, and 4 MB for older versions. The maximum size of a block blob is therefore slightly more than 4.75 TB (100 MB X 50,000 blocks) for version 2016-05-31 and later, and 195 GB (4 MB X 50,000 blocks) for all older versions. If you attempt to commit more than 50,000 blocks, the service returns status code 409 (Block List Too Long). The service also returns additional information about the error in the response, including the maximum number of blocks permitted.

The maximum number of uncommitted blocks that may be associated with a blob is 100,000, and the maximum size of the uncommitted block list is about 9.5 TB for version 2016-05-31 and later, and 400 GB for older versions.

When you call Put Block List to update an existing blob, the blob's existing properties and metadata are overwritten. However, any existing snapshots are retained with the blob. You can use the conditional request headers to perform the operation only if a specified condition is met.

If the Put Block List operation fails due to a missing block, you will need to upload the missing block.

Any uncommitted blocks will be garbage collected if there are no successful calls to Put Block or Put Block List on the blob within a week following the last successful Put Block operation. If Put Blob is called on the blob, any uncommitted blocks will be garbage collected.

If the blob has an active lease, the client must specify a valid lease ID on the request in order to commit the block list. If the client does not specify a lease ID, or specifies an invalid lease ID, the Blob service returns status code 412 (Precondition Failed). If the client specifies a lease ID but the blob does not have an active lease, the Blob service also returns status code 412 (Precondition Failed). If the client specifies a lease ID on a blob that does not yet exist, the Blob service will return status code 412 (Precondition Failed) for requests made against version 2013-08-15 and later; for prior versions the Blob service will return status code 201 (Created).

If the blob has an active lease and you call Put Block List to update the blob, the lease is maintained on the updated blob.

Put Block List applies only to block blobs. Calling Put Block List on a page blob results in status code 400 (Bad Request).

Calling Put Block List on an archived blob will return an error and on Hot/Cool blob does not change the blob tier.

See Also

Understanding Block Blobs, Append Blobs, and Page Blobs
Authentication for the Azure Storage Services
Status and Error Codes
Blob Service Error Codes
Setting Timeouts for Blob Service Operations