RE: syncbackup

[Masato Taruishi <taru@valinux.co.jp>]

> > >  * At least backup
> > >
> > >     This is a way to propagates an operation to several backup servers
> > >     at the same time and wait for at least one success result.
> > >
> > >        +------+
> > >        |Master| <--- SUCCESS ------------+
> > >        +------+                          |
> > >           | |                            |
> > >           | +------------------+         |
> > >           |                    |         |
> > >       propagation          propagation   |
> > >         XXXXX                  |         |
> > >        XhangupX               \ /        |
> > >         XXXXX               +------+     |
> > >        +------+             |Backup| +---+
> > >        |Backup|             +------+
> > >        +------+
> > >
> > >    So even if one backup server hangs up or delay because of
> > > some reason
> > >    such as network trouble, the master server can return the
> > > success to
> > >    the client as soon as possible.
> > 
> > Of course you must queue the updates to the other servers. And if one backup
> > responds for one update, but a different backup handles the next update, then
> > you have lost consistency if there are still updates in the queue.
> 
> Yes. So each update is sent to all the backup servers within a topology.
> The master manages a history information of all the backup servers upto
> where each backup server gets the result. 
> 
> Therefore, at least one backup server keeps the same directory as the
> master server. Other servers will be synchoronized later.

Basically, it's similar to back-ldap. But in back-ldap, each update is
sent to only one backup server at the same time while it's sent to all
the backup servers at the same time in syncbackup. If back-ldap use
syncbackup(), it can perform syncbackup style fanout. back-ldap has
more convenient features which syncbackup doesn't have, such as map
or fanout of search operation.

-- 
Masato Taruishi <taru@valinux.co.jp>