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From "Sridhar Komandur" <anon2...@komandur.com>
Subject Re: improve master/slave topology
Date Wed, 08 Mar 2006 21:29:12 GMT
I agree that bulk synch first and then enabling dynamic synch cuts on down
complexity.

Please see answers inline ...

On 3/8/06, Rob Davies <rajdavies@gmail.com> wrote:
>
> Is not that simple - while the slave is syncing, there are also
> running clients that are acknowledging messages (and hence they get
> deleted).


These new messages will be part of the dynamic sync. Note that the slave has
the option of not acting on it right away.

We could record all the message exchanges (adds/deletes/new durable
> subscribers/delete subscribers etc. etc.) - but is it really likely
> that the slave will ever catch up without a pause ?
>
This type of synchronization gets very difficult very quickly. We
> haven't even gone through edge cases (fail-over scenarios whilst the
> master/slave are still syncing for example).



I am not sure if it is fruitful to record and send every message  to the
slave. Slave is recreating the state of the master, so only
summary/outstanding info at tthe master that is of relevance to recreating
slave state should be sent. I  am not yet familiar enough with activemq to
delve into specific design details.

Which is why my preference is pause processing whilst a bulk transfer
> happens. In reality,  as we prefer shared-nothing architectures, this
> involves copying journal files and database files from one machine to
> another - which can be done relatively quickly - so pausing the
> clients won't be too onerous.
>
> cheers,
>
> Rob



So, just to clarify,  when bulk sync is happening what happens to the
messages from  producers (are they also blocked) ?How putting the new
messages in a 'holding' area, while sending them to the slave - slave is in
a 'bulk synch' state and would do the same.


As I mentioned, waiting for bulk transfer to finish simplies design. It also
gives us an opportunity to evaluate if the pain of pausing the clients is
worth the additional complexity.

Regards
- Sridhar


I
> On 8 Mar 2006, at 19:28, Sridhar Komandur wrote:
>
> > On 3/8/06, Ning Li <Ning.Li@businessobjects.com> wrote:
> >>
> >> Bulk synch is a good idea, I think we can find a way to do it in
> >> current
> >> system, like create a topic and every message comes in will be
> >> sent to
> >> that topic, when the secondary comes up, it can pull those
> >> messages. Or
> >> we can find other ways to do it.
> >
> >
> > Yes, an internally created (persisted) queue at the primary
> > to store stuff when the secondary is not in sight.  When the
> > secondary comes
> > up
> > it drains from that subject ? Sounds like a good idea to me.
> >
> >
> > One difficulty is we cannot pause the primary broker, it is hard
> > for the
> >> secondary to catch up with both the historic and ongoing messages, I
> >> think there is a timing issue in it. I guess that is why James
> >> recommended pausing the primary broker.
> >>
> >> I am not sure if we can find a way to do both dynamic synch and bulk
> >> synch at the same time in the current system that will be great.
> >
> >
> >
> > It can be done - we need a notion of ordering among all the
> > messages (coming
> > from both dynamic as well as bulk synch). This ordering can be
> > provided by
> > the message arrival  time stamp  at the primary.
> >
> > Once we do this it is a matter of inserting the incoming messages
> > (without
> > worrying about the source) to the same target store. We can even
> > have the
> > bulk synch proceed in a lazy fashion - a background task at the
> > primary (and
> > possibly at the secondary) for a couple of reasons:
> >  - latest messages are more relevant/important
> > -  latest messages could in fact be retransmissions of the old, so
> > it is ok
> > to process the old messeges later for recovery purposes
> >
> > Regards
> > - Sridhar
> >
> > Thanks.
> >>
> >> Ning
> >> -----Original Message-----
> >> From: sridharkomandur@gmail.com [mailto:sridharkomandur@gmail.com] On
> >> Behalf Of Sridhar Komandur
> >> Sent: Wednesday, March 08, 2006 9:59 AM
> >> To: activemq-dev@geronimo.apache.org
> >> Subject: Re: improve master/slave topology
> >>
> >> I like the idea of broker-broker synchronization. One of the
> >> issues to
> >> resolve is how reliable this synch activity needs to be ? A
> >> transactional
> >> approach is too heavy weight for the common case.
> >>
> >> I think a middle ground based on TCP may be good enough. We can
> >> divide
> >> the
> >> synchronization into two phases:
> >> - dynamic synch : messages are sent to the partner on an ongoing
> >> basis
> >> - bulk synch: a new secondary comes up and its state needs to be
> >> brought
> >> up
> >> to par with primary
> >>
> >> Thanks
> >> Regards
> >> - Sridhar
> >>
> >> On 3/6/06, Ning Li <Ning.Li@businessobjects.com> wrote:
> >>>
> >>> Hi,
> >>>
> >>> This is a continued discussion about dynamically reintroduce the
> >> master
> >>> after a failure, the original discussion is here.
> >>>
> >>> http://forums.activemq.org/posts/list/468.page#1653
> >>>
> >>> James idea about pausing the slave and synchronize two DBs is better
> >>> than stopping the slave and doing a manual sync. But I doubt this is
> >>> acceptable to us, as in real production environment, we won't be
> >>> able
> >> to
> >>> pause the only message broker unless for a really short interval (I
> >>> guess have to less than one minute otherwise the end user will
> >>> notice
> >>> it).
> >>>
> >>> Maybe a broker-broker synchronization protocol is the ultimate
> >> solution,
> >>> just we are not sure how to get there. Any recommendation or
> >>> suggestions?
> >>>
> >>>
> >>> Thanks
> >>>
> >>> Ning
> >>>
> >>
>
>

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