[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3801: Clarify behavior of overwriting in immutable uploads

[Tahoe-LAFS]

#3801: Clarify behavior of overwriting in immutable uploads
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     Reporter:  itamarst  |      Owner:  itamarst
         Type:  task      |     Status:  new
     Priority:  normal    |  Milestone:  HTTP Storage Protocol
    Component:  unknown   |    Version:  n/a
   Resolution:            |   Keywords:
Launchpad Bug:            |
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Comment (by itamarst):

 After further discussion, and learning that storage servers wipe in-
 progress uploads on startup:

 1. We will change semantics such that out-of-order uploads are explicitly
 allowed, but overlapping writes are explicitly disallowed.
 2. In order to prevent overlapping writes, metadata tracking what ranges
 have already been uploaded will be tracked in-memory.
 3. Later, and out of scope for this ticket, interaction with
 `IStorageServer` may need some tweaks to maximize HTTP's ability to do
 parallel uploads.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3801#comment:4>
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