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Object Versioning

Overview

Object versioning in swift is implemented by setting a flag on the container to tell swift to version all objects in the container. The flag is the X-Versions-Location header on the container, and its value is the container where the versions are stored. It is recommended to use a different X-Versions-Location container for each container that is being versioned.

When data is PUT into a versioned container (a container with the versioning flag turned on), the existing data in the file is redirected to a new object and the data in the PUT request is saved as the data for the versioned object. The new object name (for the previous version) is <versions_container>/<length><object_name>/<timestamp>, where length is the 2-character zero-padded hexidecimal length of the <object_name> and <timestamp> is the timestamp of when the previous version was created.

A GET to a versioned object will return the current version of the object without having to do any request redirects or metadata lookups.

A POST to a versioned object will update the object metadata as normal, but will not create a new version of the object. In other words, new versions are only created when the content of the object changes.

A DELETE to a versioned object will only remove the current version of the object. If you have 5 total versions of the object, you must delete the object 5 times to completely remove the object.

Note: A large object manifest file cannot be versioned, but a large object manifest may point to versioned segments.

How to Enable Object Versioning in a Swift Cluster

Set allow_versions to True in the container server config.

Examples Using curl

First, create a container with the X-Versions-Location header or add the header to an existing container. Also make sure the container referenced by the X-Versions-Location exists. In this example, the name of that container is "versions":

curl -i -XPUT -H "X-Auth-Token: <token>" \
    -H "X-Versions-Location: versions" http://<storage_url>/container
curl -i -XPUT -H "X-Auth-Token: <token>" http://<storage_url>/versions

Create an object (the first version):

curl -i -XPUT --data-binary 1 -H "X-Auth-Token: <token>" \
    http://<storage_url>/container/myobject

Now create a new version of that object:

curl -i -XPUT --data-binary 2 -H "X-Auth-Token: <token>" \
    http://<storage_url>/container/myobject

See a listing of the older versions of the object:

curl -i -H "X-Auth-Token: <token>" \
    http://<storage_url>/versions?prefix=myobject/

Now delete the current version of the object and see that the older version is gone:

curl -i -XDELETE -H "X-Auth-Token: <token>" \
    http://<storage_url>/container/myobject
curl -i -H "X-Auth-Token: <token>" \
    http://<storage_url>/versions?prefix=myobject/