[tahoe-lafs-trac-stream] [Tahoe-LAFS] #658: "tahoe cp" should avoid full upload/download when the destination already exists (using backupdb and/or plaintext hashes)

[Tahoe-LAFS]

#658: "tahoe cp" should avoid full upload/download when the destination already
exists (using backupdb and/or plaintext hashes)
-------------------------+-------------------------------------------------
     Reporter:  warner   |      Owner:
         Type:           |     Status:  new
  enhancement            |  Milestone:  undecided
     Priority:  major    |    Version:  1.3.0
    Component:  code-    |   Keywords:  backupdb tahoe-cp usability newcaps
  frontend-cli           |  performance
   Resolution:           |
Launchpad Bug:           |
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Changes (by lpirl):

 * cc: tahoe-lafs.org@… (added)


Old description:

> Now that the backupdb seems to be working well for "tahoe backup", it's
> time to extend "tahoe cp" to use it too.
>
> In the upload direction (tahoe cp LOCAL REMOTE), the backupdb should be
> used to let us skip a new upload of a file that's already been uploaded.
> The goal is to allow periodic "tahoe cp LOCAL REMOTE" (with fixed values
> of LOCAL and REMOTE) to do as little work as possible.
>
> In the download direction (tahoe cp REMOTE LOCAL), the backupdb should
> also be used, to let us skip a download of a file that's already been
> downloaded. When a Tahoe file is downloaded and written to local disk, a
> path+timestamps-to-URI entry should be added to the db. Before
> downloading a file to local disk, the disk should be checked for an
> existing file with the same timestamps: if present, and if the URI
> matches the URI that was going to be downloaded, the download should be
> skipped.

New description:

 Now that the backupdb seems to be working well for "tahoe backup", it's
 time to extend "tahoe cp" to use it too.

 In the upload direction (tahoe cp LOCAL REMOTE), the backupdb should be
 used to let us skip a new upload of a file that's already been uploaded.
 The goal is to allow periodic "tahoe cp LOCAL REMOTE" (with fixed values
 of LOCAL and REMOTE) to do as little work as possible.

 In the download direction (tahoe cp REMOTE LOCAL), the backupdb should
 also be used, to let us skip a download of a file that's already been
 downloaded. When a Tahoe file is downloaded and written to local disk, a
 path+timestamps-to-URI entry should be added to the db. Before downloading
 a file to local disk, the disk should be checked for an existing file with
 the same timestamps: if present, and if the URI matches the URI that was
 going to be downloaded, the download should be skipped.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/658#comment:6>
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