[Pgcluster-general] rlog issue

[mitani]

Hi, Markus,

> so if i keep my configuration as mentioned only overhead is produced,
> because each query to cluster2 is sent to replicator2 and then
> replicator2 will check if query was executed. right?

In order to keep a data consistency, all cluster should send replication request to the single (master) replication server.
In your case, the replicator1 should be a master replicator, and the replicator2 should be a stand-by replicator.

> another question:
> will replication work if i keep the mentioned config but remove
> cascading and rlog??

Exactly, the cascade and the rlog are additional options of replication.
It is not necessary for simple replication.


Regards,
----------------
At.Mitani


On Mon, 30 Jun 2008 16:11:50 +0200
Markus Schmidleitner <markus.schmidleitner at ocilion.com> wrote:

> Hi Mitani,
> thank you for your quick answer!
> 
> > Hi Markus,
> > 
> > First of all, compsition of replication server is single master and multi slave.
> > Therefor, cluster2 should be use replicator1 as same as cluster1.
> > 
> > As you know, rlog data alway send to lower replication server from upper replication server.
> > If upper replication server failed down during replicating commit query, 
> > lower replication server might send rlog commands to each clusters in order to finish transaction.
> > 
> ok, now i understand a bit more!
> 
> so if i keep my configuration as mentioned only overhead is produced,
> because each query to cluster2 is sent to replicator2 and then
> replicator2 will check if query was executed. right?
> 
> > I know that this rlog function is a bit complicated.
> > When you have any question, please feel free to inquire.
> > 
> > Regards,
> > --------------
> > At.Mitani
> 
> another question:
> will replication work if i keep the mentioned config but remove
> cascading and rlog??
> 
> Regards,
> Markus Schmidleitner
> 
> > -- original message --
> > From: Markus Schmidleitner<markus.schmidleitner at ocilion.com>
> > To: <pgcluster-general at pgfoundry.org>
> > Sent: Fri, 27 Jun 2008 09:50:11 +0200
> > Subject: [Pgcluster-general] rlog issue
> > 
> > >hi list, hi mitani!
> > >
> > >i'm currently working on backporting some stuff from the cybercluster
> > >project to pgcluster and doing some code-refactoring (make
> > >network-operations centralized and non-blocking, remove dead code and so
> > >on).
> > >
> > >while invastigating the rlog code i found out that rlog's are always
> > >sent to lower cascade but never to the upper one. could anyone explain
> > >why?
> > >
> > >
> > >for example assume following system composition:
> > >
> > >replicator1 ---- replicator2
> > >     |      \  /     |
> > >     |       /\      |
> > >     |      /  \     |
> > >     |     /    \    |
> > >  cluster1       cluster2
> > >
> > >
> > >- cluster1 has replicator1 as replication server
> > >- cluster2 has replicator2 as replication server
> > >- replicator1 has cluster1 and cluster2 as cluster server
> > >- replicator2 has cluster1 and cluster2 as cluster server
> > >- replicator1 is upper and replicator2 is lower
> > >
> > >(i know this is quiet a little strange config but it is necessary for us
> > >- we have multiple database nodes (server) and each of them runs a
> > >cluster and a replication server - each cluster is connected to it's
> > >local replicator, each replicator is connected to all clusters and the
> > >replicators are cascaded)
> > >
> > >
> > >for example performing INSERT on cluster1:
> > >
> > >？？as far as i understand rlog is working the following way:
> > >  1. cluster1 sends query to replicator1
> > >  2. replicator sends query over rlog-method to lower cascade
> > >(replicator2)
> > >  3. replicator1 executes query on cluster2 and cluster1 (eg. sends some
> > >ok-message to source (cluster1) and executing query on cluster2)
> > >  4. cluster2 sends query to replicator2
> > >  5. replicator2 recognizes the executing query comes from rlog, check
> > >wheter the query was executed on cluster2 and send result back to
> > >cluster2
> > >  6. cluster2 and cluster1 send result back to replicator1
> > >  7. replicator1 send some ok-message back to cluster1 (source)
> > >
> > >i think that's a short description of how rlog is working.
> > >
> > >
> > >so what about if source is cluster2?
> > >replicator2 will not perform any rlog becouse rlog-messages are only
> > >sent to lower cascade! 
> > >is this expected behavior or a bug????
> > >
> > >is there any other check to prevent replication missbehavior and if so,
> > >why using still rlog? am i missing something?
> > >
> > >
> > >my backport is working nicely so far and as soon as i finished all of my
> > >tests i will put a patch on the list!
> > >
> > >
> > >regards,
> > >Markus Schmidleitner
> > >
> > >
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-- 
mitani <mitani at sraw.co.jp>