Subject: "Clustering"

From: Peter Eisentraut <[email-masked]>
Date: Mon, 20 Nov 2006 20:25:06 +0100

The heading "Multi-Master Replication Using Clustering" doesn't make 
sense to me.  Clustering is bunching more than host together to achieve 
a common goal.  Thus multimaster replication may be a way to achieve 
clustering, but clustering is not a way to achieve multimaster 
replication.  I don't actually see clustering defined in the 
documentation.  Can someone explain the categorization?

(FWIW, I think "Clustering For Parallel Query Execution" later in the 
list is an appropriate use of the term.)

-- 
Peter Eisentraut
http://developer.postgresql.org/~petere/

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From: Bruce Momjian <[email-masked]>
Date: Mon, 20 Nov 2006 17:18:29 -0500 (EST)

> documentation.  Can someone explain the categorization?

I used the term clustering to mean that the servers work closely
together.  This is not as true with the other items on the page that are
not clustering.

> list is an appropriate use of the term.)

Yes, I saw it as a similar issue.

-- 
  Bruce Momjian   [email-masked]
  EnterpriseDB    http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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From: Markus Schiltknecht <[email-masked]>
Date: Tue, 21 Nov 2006 10:42:11 +0100

Hi,

>> documentation.  Can someone explain the categorization?

AFAICS, clustering seems to have no clear definition within database 
replication.

> together.  This is not as true with the other items on the page that are

Why not simply call in "Multi Master Replication"? That implies 
clustering, doesn't it?

Perhaps you meant a Shared Nothing Cluster by referring to clustering? 
Such a definition would make more sense.

BTW, I'm slowly beginning to accept that you don't want to mix 
"Statement-Based Replication Middleware" with "Multi Master 
Replication". ;-)

>> list is an appropriate use of the term.)

That reminds me of the requirement of having Multi Master Replication in 
place to do Parallel Query Execution. Sync Multi Master Replication 
being better, while Async Multi Master Replication obviously leads to 
inconsistent responses, when queried in parallel. That may be acceptable 
in certain situations.

Again, IMHO, "Parallel Query Execution" says everything. The word 
'Clustering' does not help, because it's not defined nor commonly used 
in any helpful way (probably besides marketing).

Regards

Markus

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From: Markus Schiltknecht <[email-masked]>
Date: Tue, 21 Nov 2006 16:50:06 +0100

Hi,

> inconsistent responses, when queried in parallel. That may be acceptable 

Oops, during rereading "Clustering For Parallel Query Execution", I've 
noticed that you mention Data Partitioning as one possible way to do 
Parallel Query Execution. Thus Multi Master Replication obviously is not 
a requirement, but just another way to allow for Parallel Query 
Execution. Mentioning that as well would probably be good.

IMHO, the advice to use multiple, independent databases to do parallel 
query execution sounds a little meager. Of course it's also parallel 
query execution, but it's not what most people suspect to find under 
that section, I would guess.

Regards

Markus

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From: Bruce Momjian <[email-masked]>
Date: Tue, 21 Nov 2006 23:00:06 -0500 (EST)

> AFAICS, clustering seems to have no clear definition within database 

OK, new title is "Synchonous Multi-Master Replication", and the next
heading is "Asynchronous Multi-Master Replication".

> Why not simply call in "Multi Master Replication"? That implies 

Well, not really because of the async multi-master that is the next
item.

> "Statement-Based Replication Middleware" with "Multi Master 

OK, are they mixed now?

> inconsistent responses, when queried in parallel. That may be acceptable 

OK, I think we have that covered now.

> in any helpful way (probably besides marketing).

OK, new title is Multi-Server Parallel Query Execution.  If I have just
"Parallel Query Execution", it could be multi-process parallel
query execution.

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From: Bruce Momjian <[email-masked]>
Date: Tue, 21 Nov 2006 23:04:48 -0500 (EST)

> Execution. Mentioning that as well would probably be good.

Uh, multi-master replication allows for load balancing, but it doesn't
help a single query to run any faster.  Think of having only one query
running on the cluster.  Parallel execution allows a single query to use
more than one computer, right?

> that section, I would guess.

Uh, this confuses me.  What is missing?  You split tables across
multiple servers.