Re: Clustering & Load Balancing & Replication

Hi,

I have just read the statement that Postgres does have (with end user
assembly) multi-master replication system. Is this just PGCluster or
something else ? if it is not PGCluster, then how can this be achieved ?

Cheers,

Andy

On 24/12/06, Shoaib Mir <shoaibmir(at)gmail(dot)com> wrote:
>
> I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony
> option and you can set it up easily using pgadmin too.
>
> This link -->
> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.htmlmight help you as well.
>
> -----------------
> Shoaib Mir
> EnterpriseDB (www.enterprisedb.com)
>
> On 12/25/06, org(at)kewlstuff(dot)co(dot)za <org(at)kewlstuff(dot)co(dot)za> wrote:
> >
> > Thanks Chris,
> > I see you a core member of Slony team and a replication guru so I'll
> > look
> > into it.
> > I'm not slamming Slony I think its probably the right tool for type of
> > work
> > your company Afilias does. Just wish you would make an official Windows
> > version of Slony as well.
> > Anyway thanks for the education, and I think it would be a good thing if
> > your site on replication, was also listed on Postgresql... good
> > research.
> > Merry Xmas
> >
> > ----- Original Message -----
> > From: "Christopher Browne" <cbbrowne(at)acm(dot)org>
> > To: <pgsql-general(at)postgresql(dot)org>
> > Sent: Sunday, December 24, 2006 4:23 AM
> > Subject: Re: [GENERAL] Clustering & Load Balancing & Replication
> >
> >
> > > Centuries ago, Nostradamus foresaw when org(at)kewlstuff(dot)co(dot)za would
> > write:
> > >> Suggest you download my little application and read the
> > documentation,
> > >> you'll see its very different, maybe even interesting.
> > >> Maybe they should change that to.... Postgres DOES HAVE a free
> > >> multi-master
> > >> replication system :)
> > >
> > > It isn't systematically usable as such, without a whole lot of
> > > end-user assembly.
> > >
> > >> One comment they make.... "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."
> > >> I'm not sure I agree with that... or maybe MVCC is just fantastic....
> > I
> > >> tested it.
> > >> The 2 phase commit locking is definitely happening at record level,
> > so
> > >> only
> > >> if the multimasters all hit the same record is there the potential
> > for
> > >> lock
> > >> conflict.
> > >> Why will dB's being randomly used, hit the same records, I think its
> > a
> > >> low
> > >> probability to begin with?
> > >
> > > That's only true if you are certain that the update pattern is NOT
> > > involving a shared set of records. IN GENERAL, heavy write activity
> > > can cause locking to become mighty expensive, which is certainly a
> > > true statement.
> > >
> > >> Not happy with that, I wrote a multithreaded routine and got them to
> > all
> > >> smack the same record, it NEVER ROLLED BACK, and if there is
> > performance
> > >> degradation, I didnt notice it... again probably a testament to the
> > MVCC
> > >> design.
> > >
> > > It seems likely to me that this requires some careful validation of
> > > testing.
> > >
> > > An effect we see is that if a set of transactions are "fighting" over
> > > a single "balance" record, they will essentially serialize over that.
> > >
> > > On a system with a single CPU, it is not obvious that you'll see a
> > > degradation there because, since you only have the single CPU, it
> > > would be serializing the activity anyways.
> > >
> > > Try it out on an 8-way SMP system and you may see things differently.
> > >
> > >> In any event if you look at the documentation, you'll see SPAR is not
> >
> > >> multimaster or nothing. Can use say one server in an office and
> > another
> > >> to
> > >> pump data to a remote web site... not sure if you would even call
> > that
> > >> multimaster, thats the point, I'm not sure SPAR fits any pure theory
> > >> category.
> > >
> > > There are a few tests I could throw at it that tend to challenge
> > > replication systems vis-a-vis "fidelity of results." I otta see if I
> > > can find them in a readily deployable form.
> > >
> > > There are two notable anomalies which have been known to break
> > > replication systems:
> > >
> > > 1. Nondeterministic updates:
> > >
> > > For instance, functions that are nondeterministic:
> > >
> > > insert into rtable values (random(), now());
> > >
> > > Or result sets that are nondeterministic:
> > >
> > > insert into rtable2 (select * from mytable where some_attr='foo'
> > > order by random() limit 5); -- Where there are 25 records with
> > > some_attr='foo'
> > >
> > > 2. Value swapping:
> > >
> > > Consider the table:
> > >
> > > create table t1 (mk integer primary key, val text unique not null);
> > >
> > > insert into t1 (mk, val) values (1, 'chris');
> > > insert into t1 (mk, val) values (2, 'dave');
> > > insert into t1 (mk, val) values (3, 'brad');
> > >
> > > begin;
> > > update t1 set mk = 99 where mk = 1;
> > > update t1 set mk = 1 where mk = 3;
> > > update t1 set mk = 3 where mk = 99;
> > > commit;
> > >
> > > Is there a condition where a pause somewhere in there will cause
> > > replication to break? Note that there have been replication systems
> > > (erServer) that this set of updates can, intermittently, cause to fall
> > > over.
> > > --
> > > let name="cbbrowne" and tld="linuxfinances.info" in String.concat "@"
> > > [name;tld];;
> > > http://cbbrowne.com/info/slony.html
> > > "Feel free to contact me (flames about my english and the useless of
> >
> > > this driver will be redirected to /dev/null, oh no, it's full...)"
> > > -- Michael Beck, describing the PC-speaker sound device
> > >
> > > ---------------------------(end of
> > broadcast)---------------------------
> > > TIP 2: Don't 'kill -9' the postmaster
> > >
> >
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 5: don't forget to increase your free space map settings
> >
>
>