Azure cloud blob property vs metadata

by ingvar 5. juni 2011 21:45

Both properties (some of them) and the metadata collection of a blob can be used to store meta data for a given blob. But there are a small differences between them. When working with the blob storage, the number of HTTP REST request plays a significant role when it comes to performance. The number of request becomes very important if the blob storage contains a lot of small files. There are at least three properties found in the CloudBlob.Properties property that can be used freely. These are ContentType, ContentEncoding and ContentLanguage. These can hold very large strings! I have tried testing with a string containing 100.000 characters and it worked. They could possible hold a lot more, but hey, 100.000 is a lot! So all three of them can be used to hold meta data.
So, what are the difference of using these properties and using the metadata collection? The difference lies in when they get populated. This is best illustrated by the following code:

CloudBlobContainer container; /* Initialized assumed */
CloudBlob blob1 = container.GetBlobReference("MyTestBlob.txt");
blob1.Properties.ContentType = "MyType";
blob1.Metadata["Meta"] = "MyMeta";
blob1.UploadText("Some content");

CloudBlob blob2 = container.GetBlobReference("MyTestBlob.txt");
string value21 = blob2.Properties.ContentType; /* Not populated */
string value22 = blob2.Metadata["Meta"]; /* Not populated */

CloudBlob blob3 = container.GetBlobReference("MyTestBlob.txt");
blob3.FetchAttributes();
string value31 = blob3.Properties.ContentType; /* Populated */
string value32 = blob3.Metadata["Meta"]; /* Populated */

CloudBlob blob4 = (CloudBlob)container.ListBlobs().First();
string value41 = blob4.Properties.ContentType; /* Populated */
string value42 = blob4.Metadata["Meta"]; /* Not populated */

BlobRequestOptions options = new BlobRequestOptions
  {
     BlobListingDetails = BlobListingDetails.Metadata
  };
CloudBlob blob5 = (CloudBlob)container.ListBlobs(options).First();
string value51 = blob5.Properties.ContentType; /* Populated */
string value52 = blob5.Metadata["Meta"]; /* populated */

 

The difference is when using ListBlobs on a container or blob directory and the values of the BlobRequestOptions object. It might not seem to be a big difference, but imagine that there are 10.000 blobs all with a meta data string value with a length of 100 characters. That sums to 1.000.000 extra data to send when listing the blobs. So if the meta data is not used every time you do a ListBlobs call, you might consider moving it to the Metadata collection. I will investigate more into the performance of these methods of storing meta data for a blob in a later blog post.

Tags:

.NET | Azure | C# | Blob

Comments (1) -

cloud provider
cloud provider United States
18-01-2012 03:02:40 #

hey the azure clouds are for many still an enigma. thanks!

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Martin Ingvar Kofoed Jensen

Architect and Senior Developer at Composite on the open source project Composite C1 - C#/4.0, LINQ, Azure, Parallel and much more!

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