On 04/09/2013, at 5:50 PM, Ulrich Windl <[email protected]> 
wrote:

>>>> Andrew Beekhof <[email protected]> schrieb am 04.09.2013 um 08:27 in 
>>>> Nachricht
> <[email protected]>:
> 
>> On 04/09/2013, at 4:09 PM, Vladislav Bogdanov <[email protected]> wrote:
>> 
> 
> [...]
>>> Are there any possibilities/plans to implement "partial" messages?
>> 
>> This is part of the reason we send only the changes that result from an 
>> update.
> 
> I haven't checked recently, but when a lot of communication happened, 
> applying the diffs frequently failed , and a full copy was transferred.
> I guess it's due to the fact that the protocol is not a two-way (request & 
> response) diff protocol, but just a one-way "diff broadcast" protocol. So if 
> a node didn't have the previous version it cannot process the latest diff and 
> needs a full copy instead.

In this case it asks for and is sent a full copy to get it back on track.
Frequently failing diffs is symptomatic of a bug[1], not a design flaw.

[1] Eg. the one fixed by
+ Andrew Beekhof (11 months ago) 19589ee: High: Core: Prevent ordering changes 
when applying xml diffs 

>  I don't know how well this scales for big clusters with massive updates.
> 
> BTW: What are the reasons why a DC changes node while current DC-node is fine?

Communication difficulties and cib replace operations (its a low cost way to 
regenerate the status section).

> Occasionally this also happens, causing some extra communication...
> 
>> Message fragmenting would have to happen at the corosync/libqb level.
> 
> Regards,
> Ulrich
> 
> 
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