While working on Windows Azure Table Storage, I had to retrieve partition key range so I look around if there is an API to get the list of all partition keys for my whole table, unfortunately I could not find an API to ease my job. I was really looking for an efficient way to retrieve all partition keys (in a range or not) without touching all the rows within the partition.
Digging further, I found there is no built in API to get a list of partition keys, instead I would have to create a solution for myself. So I end up inserting a single dummy row into each partition and when I wanted to get a list of partition keys I just query for those dummy items and they gave me the list I was looking for.
Read more on Windows Azure Table Storage API: http://msdn.microsoft.com/en-us/library/dd179423.aspx