maria-developers team mailing list archive

[Alex Yurchenko <alexey.yurchenko@xxxxxxxxxxxxx>]

On Mon, 25 Jan 2010 11:51:24 -0800, Jeremy Zawodny <Jeremy@xxxxxxxxxxx>
wrote:
> On Mon, Jan 25, 2010 at 11:47 AM, Alex Yurchenko <
> alexey.yurchenko@xxxxxxxxxxxxx> wrote:
> 
>> On Mon, 25 Jan 2010 10:47:23 -0800, Jeremy Zawodny <Jeremy@xxxxxxxxxxx>
>> wrote:
>> > If the connection between a slave and master is interrupted, the
slave
>> > won't
>> > report itself as being "behind" until the slave's network timeout to
>> > the
>> > master expires and it reconnect (assuming it can).
>> >
>> > Jeremy
>>
>> Hi Jeremy,
>>
>> Does it mean that you want to detect network outages using the
heartbeat?
>> If so, won't it be easier to just set master-slave connection timeout
to
>> the desirable value and let replication system to handle it? I'm asking
>> this not from position of improving current replication in short term,
>> but
>> from position of whether a heartbeat function is needed in replication
>> API?
>>
> 
> Not at all.
> 
> My point is that you cannot (today) rely on MySQL slaves to "self
report"
> in
> all situations.  With a heatbeat that the master sends every N seconds
and
> the slave expects to see every N seconds, it's possible to see latency
in
> the replication stream regardless of the cause--even during weird
network
> outages that the slave won't notice until the timeout is reached.
> 
> Does that make more sense?
> 
Perhaps, but not for me really ;). Actually I still don't understand what
exactly people mean by "heartbeat" here. According to
http://dev.mysql.com/doc/refman/5.5/en/change-master-to.html it is simply a
transport keepalive. It does not even measure latency. To me it is not a
"feature" actually, it is a bugfix.

I realize that you are looking for solution to the present day situation.
What I'm trying to figure out is whether it should be a part of replication
API.

So let me ask it differently. Suppose you have a replication system that
provides cluster membership service (members come and gone) and provides
you with a latency measurement (averaged over a specified window). Would
you still need an explicit heartbeat "feature"?

Regards,
Alex


-- 
Alexey Yurchenko,
Codership Oy, www.codership.com
Skype: alexey.yurchenko, Phone: +358-400-516-011