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RE: syncbackup



>>  * 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.

Yeah. the temporal failure of backup server seems problematic with this 
approach.
One solution is to attach one more contextCSN to the update : the 
contextCSN
previously sent to one or more backup servers. When the backup server 
restarts
receiving updates after recovery, it can compare the last contextCSN it 
has received
with the previous contextCSN delivered from the master. If it defers, the 
backup
server can initiate a syncrepl to perform an incremental sync.

>  * Boot-time synchronization using syncrepl()
>
>     When another backup server fail over the master service,
> the backup
>     server fetches the changes to other servers by using one-time
>     syncrepl.
>
>        +------+
>        |XXXXXX|
>        +------+
>                                  New Master
>                   syncrepl  +------+
>        +------+    +----->  |Backup|
>        |Backup| ---+        +------+
>        +------+
>
>     The new server should be up-to-date within the available servers.

What is the assumed or preferred configuration for the HA environment ?
Is it assumed to have out-of-band heartbeat connections ?

- Jong

------------------------
Jong Hyuk Choi
IBM Thomas J. Watson Research Center - Enterprise Linux Group
P. O. Box 218, Yorktown Heights, NY 10598
email: jongchoi@us.ibm.com
(phone) 914-945-3979    (fax) 914-945-4425   TL: 862-3979