[Xapian-tickets] [Xapian] #348: Compress replication changesets

Xapian nobody at xapian.org
Mon Feb 1 23:05:03 GMT 2010


#348: Compress replication changesets
---------------------------+------------------------------------------------
 Reporter:  olly           |       Owner:  olly     
     Type:  defect         |      Status:  new      
 Priority:  high           |   Milestone:  1.1.4    
Component:  Backend-Chert  |     Version:  SVN trunk
 Severity:  normal         |    Keywords:           
Blockedby:                 |    Platform:  All      
 Blocking:                 |  
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Comment(by richard):

 I'm not fully convinced that it's sensible to always compress the
 changesets, though the argument about keeping the number of codepaths to a
 minimum seems quite compelling, and I suspect it would be an improvement
 in most cases.  CPU doesn't seem likely to be the limiting factor when
 applying changesets on the clients, but I've not enough evidence to be
 sure about that either way.

 Changesets already begin with a magic string to make the file easy to
 identify, followed by an integer version number (currently 1), so there
 would be no need to change the format on disk in a backwards incompatible
 manner to support both compressed and non-compressed changesets here: we'd
 just use version number 2 for compressed changesets.  [The version numbers
 were partly implemented with this in mind, and partly so that we could
 support other schemes in future, such as storing the sequence of key-tag
 operations involved in a changeset, rather than the block level changes.]

 If we're willing to support a second codepath for non-compressed
 changesets, we can punt this to 1.2.x. - we might need to leave
 compression off by default until 1.3.x if we did this though, so that any
 1.2.x client could read changesets from any 1.2.y server.

 I'd be happy to live with this, in the interests of getting 1.2 out the
 door.

-- 
Ticket URL: <http://trac.xapian.org/ticket/348#comment:4>
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