Re: [sqlite] Multi-master replication with updated Versioning?extension

On Thu, Jul 30, 2009 at 08:33:10PM +0400, Alexey Pechnikov scratched on the 
wall:
> Hello!
> 
> On Thursday 30 July 2009 19:47:39 Jay A. Kreibich wrote:
> >   Then again, given that ROWID values are signed 64 bit values, you
> >   could just start each master at some offset (like +0x00FFFFFFFFFFFFFF)
> >   and not worry about it.  It would still be a good idea to force all
> >   the tables into an AUTOINCREMENT mode somehow.
> 

> Before start replication databases may be copied from prototype 
> database as files and so they are binary equal.

  That still works (outside of adjustments to the sqlite_sequences
  table).
  
  Any replication function is going to manually insert a whole record,
  including the ROWID.  The AUTOINCREMENT values would only be used if
  a master has to insert a brand-new row that otherwise doesn't exist
  anywhere in the cluster of masters.  In that case it has to be
  assigned a globally unique (i.e. UUID) ROWID value.  Off-setting the
  pool of ROWID values each master uses effectively does this.

> UUID is really unique key for multi-master replication.

  And that's more or less what this does.  Any brand new record that is
  created will be assigned a globally unique ROWID value, basically
  making that ROWID a UUID.

> This is bad because ROWID without explicit field is not persistant 
> and may change after dump/restore. Please see illustration of the problem:

  Yes, this is true of almost every database system out there,
  including ones that generate UUIDs.  You're not really supposed to
  dump and restore a multi-master system.  If you trash a database you
  "restore" it by creating an empty master an syncing from a working
  master (or, in the case of SQLite, just copy of the file).  If all
  your masters are trashed and you're building a new cluster, the
  alignment of ROWID values doesn't matter; even if they're freshly
  generated they're still unique across the new one-master cluster.

   -j

-- 
Jay A. Kreibich < J A Y  @  K R E I B I.C H >

"Our opponent is an alien starship packed with atomic bombs.  We have
 a protractor."   "I'll go home and see if I can scrounge up a ruler
 and a piece of string."  --from Anathem by Neal Stephenson
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