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* Re: [Pgcluster-general] PostgreSQL Documentation of
@ 2006-11-21 03:22 Bruce Momjian <bruce@momjian.us>
0 siblings, 0 replies; 8+ messages in thread
From: Bruce Momjian @ 2006-11-21 03:22 UTC (permalink / raw)
To: Markus Schiltknecht <markus@bluegap.ch>; +Cc: a.mitani@sra-europe.com; pgsql-docs; pgcluster-general@pgfoundry.org
Markus Schiltknecht wrote:
> In the very same paper, they define what a Cluster is for them: "A
> cluster is a group of independent servers that cooperate as a single
> system. The primary cluster components are processor nodes, a cluster
> interconnect, and a shared disk subsystem. The clusters share disk
> access and resources that manage data, but the distinct hardware cluster
> nodes do not share memory."
>
> Thus, Oracle RAC seems to be a shared disk solution. Only in conjunction
> with their OCFS, you could probably call it a shared-nothing solution,
> but it's certainly not a shared-memory thing.
>
> I'd vote for explaining these terms in the PostgreSQL documentation, as
> there seems to be a lot of confusion regarding these terms.
OK, but how does explaining the terms help our users?
--
Bruce Momjian bruce@momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: [Pgcluster-general] PostgreSQL Documentation of
@ 2006-11-21 21:51 Bruce Momjian <bruce@momjian.us>
2006-11-21 21:57 ` Re: [Pgcluster-general] PostgreSQL Documentation of Joshua D. Drake <jd@commandprompt.com>
2006-11-21 22:35 ` Re: [Pgcluster-general] PostgreSQL Documentation of Markus Schiltknecht <markus@bluegap.ch>
0 siblings, 2 replies; 8+ messages in thread
From: Bruce Momjian @ 2006-11-21 21:51 UTC (permalink / raw)
To: Markus Schiltknecht <markus@bluegap.ch>; +Cc: a.mitani@sra-europe.com; pgsql-docs; pgcluster-general@pgfoundry.org
Markus Schiltknecht wrote:
> Hi,
>
> Bruce Momjian wrote:
> > I feel the shared-* issue splits us up like master/slave and
> > multi-master splits up
>
> No, not quite. To sum up, I'd say the following combinations make sense:
>
> sync, multi-master replication on shared-memory cluster (which is much
> like a super-computer. With shared memory distributing locks does not
> cost much - beside marketing, there is probably not much sense in
> calling this a cluster at all).
Wow, how is that different than an multi-CPU server? I guess I don't
see the point to it. The only value I see to it would be failover if
one of the servers fails, but it seems the failed server would be
holding locks that would make failover difficult to do without
restarting all the servers.
> sync, multi-master replication on shared-disk cluster (where locks and
> memory-caches have to be synchronized. OracleRAC and PgCluster-II fit in
> here.)
OK. I didn't think pgcluster was shared disk. I thought all the
synchronization was via the network.
> (Probably running an async replication on a shared-disk cluster would
> make sense with MVCC and in some corner cases, but I don't see much
> benefits in that.)
>
> sync, multi-master replication on shared-nothing cluster (where locks,
> caches and data needs to be synchronized over an interconnect.
> Postgres-R, PgCluster, PgPool)
Yes, I think we have that one covered.
> (sync, single-master replication does not make much sense, because if
> you go sync at all, you could as well use the nodes which run in sync).
>
> async, multi-master replication on shared-nothing cluster (i.e. Slony-I)
Covered.
> async, single-master replication on shared-nothing cluster (mainly for
> failover purpose, you mention solutions for that)
Added as a new entry calld Conflict Resolution.
> For me these categorizations are important and help a good deal to
> ensure what I'm talking about with somebody. The documentation is much
> more focused on individual solutions, sometimes avoiding to categorize
> them. I would love to get others opinions, but as not many others speak
> up, I just accept it that way.
One problem I have is that we we have shared disk failover, but no other
shared case with a PostgreSQL implementation, and people don't want to
mention Oracle RAC, so why do we mention it if we have no
implementations even in the works.
> > Yea, gets confusing.
>
> Well, Oracle also does a good deal in making it confusing, IMO.
>
> > Good point. I mentioned Oracle RAC only because it seems to be an
> > industry standard, so by mentioning it, people know exactly what we are
> > talking about.
>
> That's a point, even if I don't really know how much of an industry
> standard it is. But given how badly Oracle does in explaining basics of
> replication and clustering, I think it's not very beneficial.
OK, agreed, removed.
> > Is there a better way? And people do ask for Oracle
> > RAC, so in a way we are telling them we don't have something similar.
> > As sad as that is, it is true currently.
>
> How far is PGCluster-II? Does it make sense to mention it? Can
> PGCluster-II be used with network filesystems like NFS, OCFS2 or the like?
I am waiting for email from Mitani-san, the pgcluster author.
>
> > pgcluster is must closer to Oracle RAC,
>
> Why do you think so? Oracle RAC is mainly based on a shared disk
> cluster, where PGCluster bases on a shared nothing architecture.
> PGCluster-II seems closer to Oracle RAC, for me.
Oh, I am not aware of pgcluster-II. Did you mean pgpool-II? I think
so. I have mentioned pgpool-II now as part of Clustering For Parallel
Query Execution. Is that OK?
--
Bruce Momjian bruce@momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: [Pgcluster-general] PostgreSQL Documentation of
2006-11-21 21:51 Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
@ 2006-11-21 21:57 ` Joshua D. Drake <jd@commandprompt.com>
2006-11-21 22:31 ` Re: [Pgcluster-general] PostgreSQL Documentation of Markus Schiltknecht <markus@bluegap.ch>
2006-11-21 22:45 ` Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
1 sibling, 2 replies; 8+ messages in thread
From: Joshua D. Drake @ 2006-11-21 21:57 UTC (permalink / raw)
To: Bruce Momjian <bruce@momjian.us>; +Cc: Markus Schiltknecht <markus@bluegap.ch>; a.mitani@sra-europe.com; pgsql-docs; pgcluster-general@pgfoundry.org
On Tue, 2006-11-21 at 16:51 -0500, Bruce Momjian wrote:
> Markus Schiltknecht wrote:
> > Hi,
> >
> > Bruce Momjian wrote:
> > > I feel the shared-* issue splits us up like master/slave and
> > > multi-master splits up
> >
> > No, not quite. To sum up, I'd say the following combinations make sense:
> >
> > sync, multi-master replication on shared-memory cluster (which is much
> > like a super-computer. With shared memory distributing locks does not
> > cost much - beside marketing, there is probably not much sense in
> > calling this a cluster at all).
>
> Wow, how is that different than an multi-CPU server?
You can't have 1000 cpus :).. You can have 1000 dual core servers.
Joshua D. Drake
--
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^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: [Pgcluster-general] PostgreSQL Documentation of
2006-11-21 21:51 Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
2006-11-21 21:57 ` Re: [Pgcluster-general] PostgreSQL Documentation of Joshua D. Drake <jd@commandprompt.com>
@ 2006-11-21 22:31 ` Markus Schiltknecht <markus@bluegap.ch>
1 sibling, 0 replies; 8+ messages in thread
From: Markus Schiltknecht @ 2006-11-21 22:31 UTC (permalink / raw)
To: Joshua D. Drake <jd@commandprompt.com>; +Cc: Bruce Momjian <bruce@momjian.us>; a.mitani@sra-europe.com; pgsql-docs; pgcluster-general@pgfoundry.org
Joshua D. Drake wrote:
> On Tue, 2006-11-21 at 16:51 -0500, Bruce Momjian wrote:
>> Markus Schiltknecht wrote:
>>> Hi,
>>>
>>> Bruce Momjian wrote:
>>>> I feel the shared-* issue splits us up like master/slave and
>>>> multi-master splits up
>>> No, not quite. To sum up, I'd say the following combinations make sense:
>>>
>>> sync, multi-master replication on shared-memory cluster (which is much
>>> like a super-computer. With shared memory distributing locks does not
>>> cost much - beside marketing, there is probably not much sense in
>>> calling this a cluster at all).
>> Wow, how is that different than an multi-CPU server?
>
> You can't have 1000 cpus :).. You can have 1000 dual core servers.
Have them share all their memory is the challenge, though. Ask IBM, they
certainly do big-irons like that.
As I said, it's like a super-computer, but you can also see it as a
cluster of CPUs with shared memory and shared disks. It's all just a
matter of your point of view.
Regards
Markus
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: [Pgcluster-general] PostgreSQL Documentation of
2006-11-21 21:51 Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
2006-11-21 21:57 ` Re: [Pgcluster-general] PostgreSQL Documentation of Joshua D. Drake <jd@commandprompt.com>
@ 2006-11-21 22:45 ` Bruce Momjian <bruce@momjian.us>
1 sibling, 0 replies; 8+ messages in thread
From: Bruce Momjian @ 2006-11-21 22:45 UTC (permalink / raw)
To: Joshua D. Drake <jd@commandprompt.com>; +Cc: Markus Schiltknecht <markus@bluegap.ch>; a.mitani@sra-europe.com; pgsql-docs; pgcluster-general@pgfoundry.org
Joshua D. Drake wrote:
> On Tue, 2006-11-21 at 16:51 -0500, Bruce Momjian wrote:
> > Markus Schiltknecht wrote:
> > > Hi,
> > >
> > > Bruce Momjian wrote:
> > > > I feel the shared-* issue splits us up like master/slave and
> > > > multi-master splits up
> > >
> > > No, not quite. To sum up, I'd say the following combinations make sense:
> > >
> > > sync, multi-master replication on shared-memory cluster (which is much
> > > like a super-computer. With shared memory distributing locks does not
> > > cost much - beside marketing, there is probably not much sense in
> > > calling this a cluster at all).
> >
> > Wow, how is that different than an multi-CPU server?
>
> You can't have 1000 cpus :).. You can have 1000 dual core servers.
But does anyone make a shared-memory cluster that can do 1000 cpu's?
Sounds like Sequent, but I didn't think anyone was doing this anymore.
--
Bruce Momjian bruce@momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: [Pgcluster-general] PostgreSQL Documentation of
2006-11-21 21:51 Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
@ 2006-11-21 22:35 ` Markus Schiltknecht <markus@bluegap.ch>
2006-11-22 04:28 ` Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
1 sibling, 1 reply; 8+ messages in thread
From: Markus Schiltknecht @ 2006-11-21 22:35 UTC (permalink / raw)
To: Bruce Momjian <bruce@momjian.us>; +Cc: a.mitani@sra-europe.com; pgsql-docs; pgcluster-general@pgfoundry.org
Hi,
Bruce Momjian wrote:
> Oh, I am not aware of pgcluster-II. Did you mean pgpool-II? I think
> so.
No, I really mean PGCluster-II. Didn't you attend A. Mitani's speech
about PGCluster? Check his slides:
http://conference.postgresql.org/download/TFCKUpload/62.pdf
Regards
Markus
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: [Pgcluster-general] PostgreSQL Documentation of
2006-11-21 21:51 Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
2006-11-21 22:35 ` Re: [Pgcluster-general] PostgreSQL Documentation of Markus Schiltknecht <markus@bluegap.ch>
@ 2006-11-22 04:28 ` Bruce Momjian <bruce@momjian.us>
0 siblings, 0 replies; 8+ messages in thread
From: Bruce Momjian @ 2006-11-22 04:28 UTC (permalink / raw)
To: Markus Schiltknecht <markus@bluegap.ch>; +Cc: a.mitani@sra-europe.com; pgsql-docs; pgcluster-general@pgfoundry.org
Markus Schiltknecht wrote:
> Hi,
>
> Bruce Momjian wrote:
> > Oh, I am not aware of pgcluster-II. Did you mean pgpool-II? I think
> > so.
>
> No, I really mean PGCluster-II. Didn't you attend A. Mitani's speech
> about PGCluster? Check his slides:
>
> http://conference.postgresql.org/download/TFCKUpload/62.pdf
I just saw it. It does seem more like Oracle RAC than any other method.
--
Bruce Momjian bruce@momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: [Pgcluster-general] PostgreSQL Documentation of
@ 2006-11-22 03:44 Bruce Momjian <bruce@momjian.us>
0 siblings, 0 replies; 8+ messages in thread
From: Bruce Momjian @ 2006-11-22 03:44 UTC (permalink / raw)
To: Markus Schiltknecht <markus@bluegap.ch>; +Cc: a.mitani@sra-europe.com; pgsql-docs
Markus Schiltknecht wrote:
> Hello Bruce,
>
> Bruce Momjian wrote:
> > OK, but how does explaining the terms help our users?
>
> As we even have on sort-of-a solution for shared disk clusters (the
> Shared Disk Failover part), we should explain this term (as you already
> do there).
>
> Clarifying that all other solutions are for shared nothing clusters
> makes sense, IMO. We don't necessarily need to go into shared memory and
> the confusion which shared everything introduced. OTOH, where else to
> enlighten people about that if not in such a documentation?
>
> To answer your question: by explaining these terms, they are
> demystified. The users will understand the experts better and have some
> fundamental terms which they can base their discussion on. Of course
> it's questionable how far to go, and we are debating just that now, I think.
>
> But I have no doubt in the OSS tradition of good documentation. Long
> live the saying 'RTFM'! :-)
I figured that shared-disk/memory only really makes sense for
multi-master clustering, so I mentioned it in that paragraph:
<term>Multi-Master Clustering</term>
<listitem>
<para>
In clustering, each server can accept write requests, and
modified data is transmitted from the original server to every
other server before each transaction commits. Heavy write
activity can cause excessive locking, leading to poor performance.
In fact, write performance is often worse than that of a single
-> server. Read requests can be sent to any server. Some
-> implementations use cluster-wide shared memory or shared disk
-> to reduce the communication overhead. Clustering is best for
mostly read workloads, though its big advantage is that any
server can accept write requests — there is no need to
partition workloads between master and slave servers, and
because the data changes are sent from one server to another,
there is no problem with non-deterministic functions like
<function>random()</>.
Is that enought?
--
Bruce Momjian bruce@momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
^ permalink raw reply [nested|flat] 8+ messages in thread
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2006-11-21 03:22 Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
2006-11-21 21:51 Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
2006-11-21 21:57 ` Joshua D. Drake <jd@commandprompt.com>
2006-11-21 22:31 ` Markus Schiltknecht <markus@bluegap.ch>
2006-11-21 22:45 ` Bruce Momjian <bruce@momjian.us>
2006-11-21 22:35 ` Markus Schiltknecht <markus@bluegap.ch>
2006-11-22 04:28 ` Bruce Momjian <bruce@momjian.us>
2006-11-22 03:44 Re: [Pgcluster-general] PostgreSQL Documentation of Bruce Momjian <bruce@momjian.us>
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