[tahoe-lafs-trac-stream] [tahoe-lafs] #1869: pluggable backends: serialize backend operations on a shareset

[tahoe-lafs]

#1869: pluggable backends: serialize backend operations on a shareset
-------------------------------------------------+-------------------------
 Reporter:  davidsarah                           |          Owner:
     Type:  defect                               |  davidsarah
 Priority:  normal                               |         Status:  new
Component:  code-storage                         |      Milestone:  1.11.0
 Keywords:  cloud-backend storage shareset       |        Version:  cloud-
  cache                                          |  branch
                                                 |  Launchpad Bug:
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 The following issue needs to be fixed before the pluggable backends code
 is merged to trunk (#1819). Before pluggable backends, operations that
 access share storage were synchronous, and so two or more such operations
 could not run concurrently. This is important because clients make the
 assumption of serializability for accesses to a mutable share on a given
 server (if they are the only such client, which is implied by the Prime
 Coordination Directive).

 Now that backend operations are asynchronous, they can run concurrently.
 That needs to be fixed. Note that operations on different sharesets do
 ''not'' need to be serializable with respect to each other (that would
 impose unnecessary delays).

 The simplest way to implement this is probably to have a weak cache
 mapping storage indices to ShareSet objects, so that there can only be one
 ShareSet object per actual shareset, and then use a deferred queue in the
 ShareSet object to serialize operations. I'm not sure exactly where the
 cache should go yet.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1869>
tahoe-lafs <https://tahoe-lafs.org>
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