[sheepdog] [RFC] create onode before uploading object completed

[MORITA Kazutaka]

At Mon, 6 Jan 2014 17:16:22 +0800,
Robin Dong wrote:
> 
> Hi All,
> 
> At present, the implemention of swift interface for creating object in
> sheepdog is:
> 
> 1. lock container
> 2. check whether the onode with same object name is exists.
> 3. unlock container
> 4. upload object
> 5. create onode
> 
> this sequence have a problem: if two clients uploading same objects
> concurrently, it will create two
> objects with same names in container.To avoid duplicated names, we must put
> "create onode"
> operation in container lock regions.
> 
> Therefore we need to change the processes of creating object to:
> 
> 1. lock container
> 2. check whether the onode is exists.
> 3. allocate data space for object, and create onode, then write it done
> 4. unlock container
> 5. upload object
> 
> this routine will avoid uploading duplicated objects.
> 
> There is an exception on the new routine: if the client halt the uploading
> progress, we will have a
> "uploading uncompleted" onode.
> I think this problem is easy to solve: we can add code for onode to
> identify its status.
> A new onode will be set to "INIT", and after uploading completed, the onode
> will be set to  "COMPLETED".

Then, the procedure will be as follows?

  1. lock container
  2. check whether the onode is exists.
  3. allocate data space for object, and create onode, then write it done
  4. mark the onode as "INIT"
  5. unlock container
  6. upload object
  7. mark the onode as "COMPLETED"

I'm not against this suggestion, but I'm wondering whether we can get
enough performance with this approach.  IIUC, this introduces
additional write requests to the created onode at 7.

I've been evaluating Swift these days and noticed that Swift can
process thousands of PUT requests per second with only 3 nodes and 100
disks.  Can Sheepdog achieve similar or better performance with the
suggestion?

Thanks,

Kazutaka