Re: Clustering & Load Balancing & Replication

The issue i had with pgpool (1 or 2) was that (correct me if i am wrong) you
had to start the pgpool cluster with both nodes in the same state. I
thought this would mean that if you had a DB fail, before you could
re-introduce it into the pgpool cluster you would have to manually sync it
with the cluster state, is this correct ??

The system i need multi master sync for is highly transactional, so if the
behaviour i stated above is correct it is not suitable. I have tried
s-lony, and while i was pleased with the performance, it is only Single
Master - Multi Slave which is not acceptable as well.

Andy

On 26/12/06, Shoaib Mir <shoaibmir(at)gmail(dot)com> wrote:
>
> pgpool-II might help you there too I guess...
>
> ---------------
> Shoaib Mir
> EnterpriseDB (www.enterprisedb.com)
>
> On 12/26/06, Andy Dale <andy(dot)dale(at)gmail(dot)com> wrote:
> >
> > 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
> > > >
> > >
> > >
> >
>