[ClusterLabs] Buffer overflow (re-transmission list)

[satish kumar]

Is there any guidance table for window_size and max_messages with different
node configuration. Or do I have to experiment each time to get the correct
values.

On Mon, Jan 2, 2017 at 5:35 PM, Jan Friesse <jfriesse at redhat.com> wrote:

> Hello,
>>
>> I have a four node cluster. Each node connected with a centralized switch.
>> MTU size is default, 1500. On each node, a program continuously tries to
>> multi-cast as many messages as possible. With the default settings
>> (corosync.conf), buffer overflow does *not* occur till program runs on
>> three nodes. However as soon as fourth node start multi-casting, overflow
>> occur and significantly reduce the performance.
>>
>> Why buffer overflow with just four nodes?
>>
>> Is hardware topology, centralized switch, is not correct?
>>
>
> Centralized switch is ok.
>
>
>> Later, I reduced window_size and max_messages to 20 and 5 respectively. No
>> overflow but not sure whether performance is as expected.
>>
>> I would like to better understand these two parameters. Lets say in a
>> cluster of four nodes, I have window_size 50 and max_messages also set to
>> 50. Does that mean only one node will be able to multi-cast in a single
>> token rotation? If one node was not able to multi-cast because window_size
>>
>
> Not exactly. Token contains "backlog" field which is updated by all
> members. This backlog is then used to find out if there is not a member who
> wasn't able to send messages (whose backlog is too big). So let's say one
> node sent a lot messages in one round, and second node sent no messages. In
> next round, first node finds out this information and its number of allowed
> messages to sent is lowered (or in extreme case goes
> to zero) so second node can send some messages.
>
> Regards,
>   Honza
>
> is reached, when and how this node will get opportunity to send message?
>>
>> Thanks,
>> Satish
>>
>>
>>
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