On July 1, 2004 07:53 am, Ramon Salvad? wrote:
> En/na Jan Wieck ha escrit:
> > On 7/1/2004 8:23 AM, Ramon Salvad? wrote:
> >> -----BEGIN PGP SIGNED MESSAGE-----
> >> Hash: SHA1
> >>
> >> Hello,
> >>
> >> ~    I am currently learning how slony works ( I have a master-slave
> >> cluster working as intended ). I would like to know the following if
> >> possible (or some advice about it):
> >>
> >> ~    1) Is it wise to use slony to replicate a database of about 80GB
> >> (1 Master and 2 or 3 slaves) (about 100 application users concurrently).
> >
> > The size of the database isn't the determining factor. What counts is
> > the read/write ratio of your application. Slony has for example no
> > problem to replicate even the Order-Mix of a TPC-W benchmark, which is
> > about 10-15% write queries with defined think times on the client side
> > (like a real web application). But it has little chance to keep up
> > with a pgbench, which is 75% write queries done by libpq clients
> > hammering transaction after transaction as fast as they can (not
> > really any kind of realistic application).
>
> Right, I should have figured that myself. However a sentence in the
> documentacion about the inability to replicate large objects got me a
> bit confused.

Large_objects are a postgresql datatype.

>
> >> ~    2) Would it be possible to use LVS to access db slaves as a
> >> cluster from the client application (web application)? Is it a good
> >> idea?
> >
> > I would think that depends on the application, and I don't know
> > exactly how LVS works. Each replica is independant, so they can
> > possibly all represent a different point in time. That means, if a
> > user gets a search result from one server, and then tries to do a
> > detail view and the load balancer sends this request to another
> > server, this detail might not have been propagated to this server yet.
> >
> > If the load balancer honors session ID's and directs all requests
> > belonging to one session to the same server, then there should not be
> > any problem.
> >
> >
> > Jan
>
> A LVS Director is a Layer 4 switch so no luck but it supports persistent
> connections (read connection affinity), maybe that should be enough, I
> will try...
We'd be interested in hearing about your findings on this.
>
> Is there any way to keep the slaves in sync? as I understand even if the
> slaves are all using the same source (master) for replication,  it won't
> work.
This is not possible in async replication (Sore and Forward) .  Slony-I is an 
async replication system, Slony-II will be sync.

For a bit of a breakdown of what the difference between async and sync have a 
look at the following URL:
http://asktom.oracle.com/pls/ask/f?p=4950:8:::::F4950_P8_DISPLAYID:1213436164382



>
> Thanks
> Ramon
>
>
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Darcy Buskermolen
Wavefire Technologies Corp.
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