Re: [PATCH] chunkd: add cp command, for local intra-table copies

[Jeff Garzik <jeff@garzik.org>]

On 07/06/2010 11:17 AM, Pete Zaitcev wrote:
> On Tue, 6 Jul 2010 03:24:29 -0400
> Jeff Garzik<jeff@garzik.org>  wrote:
>
>> The following patch, against current hail.git, adds the "CP" command to
>> chunkd, permitting copying from object->object inside a single table.
>
> What is it for?

Here's a real-world example.

Quoting from the S3 documentation, this describes the "PUT (copy)" 
operation, something that tabled does not yet support, but should:

	This implementation of the PUT operation creates a copy of an
	object that is already stored in Amazon S3. A PUT copy
	operation is the same as performing a GET and then a PUT.
	Adding the request header, x-amz-copy-source, makes the PUT
	operation copy the source object into the destination bucket.

Assuming that a given tabled object is already fully replicated -- 
HOPEFULLY the common case for us -- the least expensive way to implement 
this is

	for each chunkd containing object OLD_KEY

		CHO_CP(object OLD_KEY -> object NEW_KEY)

Assuming each chunkd node has the necessary free space, this method 
totally avoids using network bandwidth, when creating a copy of an object

	Jeff