Large objects

updated: 2019-08-23 19:37

Large objects

Large objects¶

To discover whether your Object Storage system supports this feature, see Discoverability or check with your service provider.

By default, the content of an object cannot be greater than 5 GB. However, you can use a number of smaller objects to construct a large object. The large object is comprised of two types of objects:

Segment objects store the object content. You can divide your content into segments and upload each segment into its own segment object. Segment objects do not have any special features. You create, update, download, and delete segment objects just as you do with normal objects.
A manifest object links the segment objects into one logical large object. When you download a manifest object, Object Storage concatenates and returns the contents of the segment objects in the response body. This behavior extends to the response headers returned by GET and HEAD requests. The Content-Length response header contains the total size of all segment objects.

Object Storage takes the ETag value of each segment, concatenates them together, and returns the MD5 checksum of the result to calculate the ETag response header value. The manifest object types are:

Static large objects

The manifest object content is an ordered list of the names of the segment objects in JSON format. See Static large objects.

Dynamic large objects

The manifest object has no content but it has a X-Object-Manifest metadata header. The value of this header is CONTAINER/PREFIX, where CONTAINER is the name of the container where the segment objects are stored, and PREFIX is a string that all segment objects have in common. See Dynamic large objects.

Note

If you use a manifest object as the source of a COPY request, the new object is a normal, and not a segment, object. If the total size of the source segment objects exceeds 5 GB, the COPY request fails. However, you can make a duplicate of the manifest object and this new object can be larger than 5 GB.

Static large objects¶

To create a static large object, divide your content into pieces and create (upload) a segment object to contain each piece.

You must record the ETag response header value that the PUT operation returns. Alternatively, you can calculate the MD5 checksum of the segment before you perform the upload and include this value in the ETag request header. This action ensures that the upload cannot corrupt your data.

List the name of each segment object along with its size and MD5 checksum in order.

Create a manifest object. Include the ?multipart-manifest=put query string at the end of the manifest object name to indicate that this is a manifest object.

The body of the PUT request on the manifest object comprises a JSON list where each element contains these attributes:

path: The container and object name in the format: CONTAINER_NAME/OBJECT_NAME.
etag: The MD5 checksum of the content of the segment object. This value must match the ETag of that object.
size_bytes: The size of the segment object. This value must match the Content-Length of that object.

Static large object manifest list¶

This example shows three segment objects. You can use several containers and the object names do not have to conform to a specific pattern, in contrast to dynamic large objects.

[
    {
        "path": "mycontainer/objseg1",
        "etag": "0228c7926b8b642dfb29554cd1f00963",
        "size_bytes": 1468006
    },
    {
        "path": "mycontainer/pseudodir/seg-obj2",
        "etag": "5bfc9ea51a00b790717eeb934fb77b9b",
        "size_bytes": 1572864
    },
    {
        "path": "other-container/seg-final",
        "etag": "b9c3da507d2557c1ddc51f27c54bae51",
        "size_bytes": 256
    }
]

The Content-Length request header must contain the length of the JSON content and not the length of the segment objects. However, after the PUT operation completes, the Content-Length metadata is set to the total length of all the object segments. A similar situation applies to the ETag. If used in the PUT operation, it must contain the MD5 checksum of the JSON content. The ETag metadata value is then set to be the MD5 checksum of the concatenated ETag values of the object segments. You can also set the Content-Type request header and custom object metadata.

When the PUT operation sees the ?multipart-manifest=put query parameter, it reads the request body and verifies that each segment object exists and that the sizes and ETags match. If there is a mismatch, the PUT operation fails.

If everything matches, the API creates the manifest object and sets the X-Static-Large-Object metadata to true to indicate that the manifest is a static object manifest.

Normally when you perform a GET operation on the manifest object, the response body contains the concatenated content of the segment objects. To download the manifest list, use the ?multipart-manifest=get query parameter. The list in the response is not formatted the same as the manifest that you originally used in the PUT operation.

If you use the DELETE operation on a manifest object, the manifest object is deleted. The segment objects are not affected. However, if you add the ?multipart-manifest=delete query parameter, the segment objects are deleted and if all are successfully deleted, the manifest object is also deleted.

To change the manifest, use a PUT operation with the ?multipart-manifest=put query parameter. This request creates a manifest object. You can also update the object metadata in the usual way.

Dynamic large objects¶

Before you can upload objects that are larger than 5 GB, you must segment them. You upload the segment objects like you do with any other object and create a dynamic large manifest object. The manifest object tells Object Storage how to find the segment objects that comprise the large object. You can still access each segment individually, but when you retrieve the manifest object, the API concatenates the segments. You can include any number of segments in a single large object.

To ensure the download works correctly, you must upload all the object segments to the same container and prefix each object name so that the segments sort in correct concatenation order.

You also create and upload a manifest file. The manifest file is a zero-byte file with the extra X-Object-Manifest CONTAINER/PREFIX header. The CONTAINER is the container the object segments are in and PREFIX is the common prefix for all the segments. You must UTF-8-encode and then URL-encode the container and common prefix in the X-Object-Manifest header.

It is best to upload all the segments first and then create or update the manifest. With this method, the full object is not available for downloading until the upload is complete. Also, you can upload a new set of segments to a second location and update the manifest to point to this new location. During the upload of the new segments, the original manifest is still available to download the first set of segments.

Upload segment of large object request: HTTP¶

PUT /API_VERSION/ACCOUNT/CONTAINER/OBJECT HTTP/1.1
Host: storage.example.com
X-Auth-Token: eaaafd18-0fed-4b3a-81b4-663c99ec1cbb
ETag: 8a964ee2a5e88be344f36c22562a6486
Content-Length: 1
X-Object-Meta-PIN: 1234

No response body is returned.

The 2``nn`` response code indicates a successful write. nn is a value from 00 to 99.

The Length Required (411) response code indicates that the request does not include a required Content-Length or Content-Type header.

The Unprocessable Entity (422) response code indicates that the MD5 checksum of the data written to the storage system does NOT match the optional ETag value.

You can continue to upload segments, like this example shows, before you upload the manifest.

Upload next segment of large object request: HTTP¶

PUT /API_VERSION/ACCOUNT/CONTAINER/OBJECT HTTP/1.1
Host: storage.example.com
X-Auth-Token: eaaafd18-0fed-4b3a-81b4-663c99ec1cbb
ETag: 8a964ee2a5e88be344f36c22562a6486
Content-Length: 1
X-Object-Meta-PIN: 1234

Next, upload the manifest. This manifest specifies the container where the object segments reside. Note that if you upload additional segments after you create the manifest, the concatenated object becomes that much larger but you do not need to recreate the manifest file for subsequent additional segments.

Upload manifest request: HTTP¶

PUT /API_VERSION/ACCOUNT/CONTAINER/OBJECT HTTP/1.1
Host: storage.clouddrive.com
X-Auth-Token: eaaafd18-0fed-4b3a-81b4-663c99ec1cbb
Content-Length: 0
X-Object-Meta-PIN: 1234
X-Object-Manifest: CONTAINER/PREFIX

Upload manifest response: HTTP¶

[...]

A GET or HEAD request on the manifest returns a Content-Type response header value that is the same as the Content-Type request header value in the PUT request that created the manifest. To change the Content- Type, reissue the PUT request.

Extra transaction information¶

You can use the X-Trans-Id-Extra request header to include extra information to help you debug any errors that might occur with large object upload and other Object Storage transactions.

The Object Storage API appends the first 32 characters of the X-Trans-Id-Extra request header value to the transaction ID value in the generated X-Trans-Id response header. You must UTF-8-encode and then URL-encode the extra transaction information before you include it in the X-Trans-Id-Extra request header.

For example, you can include extra transaction information when you upload large objects such as images.

When you upload each segment and the manifest, include the same value in the X-Trans-Id-Extra request header. If an error occurs, you can find all requests that are related to the large object upload in the Object Storage logs.

You can also use X-Trans-Id-Extra strings to help operators debug requests that fail to receive responses. The operator can search for the extra information in the logs.

Comparison of static and dynamic large objects¶

While static and dynamic objects have similar behavior, this table describes their differences:

Description	Static large object	Dynamic large object
End-to-end integrity	Assured. The list of segments includes the MD5 checksum (`ETag`) of each segment. You cannot upload the manifest object if the `ETag` in the list differs from the uploaded segment object. If a segment is somehow lost, an attempt to download the manifest object results in an error.	Not guaranteed. The eventual consistency model means that although you have uploaded a segment object, it might not appear in the container listing until later. If you download the manifest before it appears in the container, it does not form part of the content returned in response to a `GET` request.
Upload order	You must upload the segment objects before upload the manifest object.	You can upload manifest and segment objects in any order. You are recommended to upload the manifest object after the segments in case a premature download of the manifest occurs. However, this is not enforced.
Removal or addition of segment objects	You cannot add or remove segment objects from the manifest. However, you can create a completely new manifest object of the same name with a different manifest list.	You can upload new segment objects or remove existing segments. The names must simply match the `PREFIX` supplied in `X-Object-Manifest`.
Segment object size and number	Segment objects must be at least 1 MB in size (by default). The final segment object can be any size. At most, 1000 segments are supported (by default).	Segment objects can be any size.
Segment object container name	The manifest list includes the container name of each object. Segment objects can be in different containers.	All segment objects must be in the same container.
Manifest object metadata	The object has `X-Static-Large-Object` set to `true`. You do not set this metadata directly. Instead the system sets it when you `PUT` a static manifest object.	The `X-Object-Manifest` value is the `CONTAINER/PREFIX`, which indicates where the segment objects are located. You supply this request header in the `PUT` operation.
Copying the manifest object	Include the `?multipart-manifest=get` query string in the `COPY` request. The new object contains the same manifest as the original. The segment objects are not copied. Instead, both the original and new manifest objects share the same set of segment objects.	The `COPY` operation does not create a manifest object. To duplicate a manifest object, use the `GET` operation to read the value of `X-Object-Manifest` and use this value in the `X-Object-Manifest` request header in a `PUT` operation. This creates a new manifest object that shares the same set of segment objects as the original manifest object.