You probably already thought of this - but - why not just set up a 
centralized server and have each office interact to the db via a web 
interface.  Let your application enforce security (apacheSSL, use db for 
user auth) and to prevent two users from editing the same record 
simultaneously.

-r

At 06:19 PM 4/20/01 -0700, Nathan Myers wrote:

>On Fri, Apr 20, 2001 at 04:53:43PM -0700, G. Anthony Reina wrote:
> > Nathan Myers wrote:
> >
> > > Does the replication have to be reliable?  Are you equipped to
> > > reconcile databases that have got out of sync, when it's not?
> > > Will the different labs ever try to update the same existing
> > > record, or insert conflicting (unique-key) records?
> >
> > (1) Yes, of course.  (2) Willing--yes; equipped--dunno.   (3) Yes,
> > probably.
>
>Hmm, good luck.  Replication, by itself, is not hard, but it's only
>a tiny part of the job.  Most of the job is in handling failures
>and conflicts correctly, for some (usually enormous) definition of
>"correctly".
>
> > > Reliable WAN replication is harder.  Most of the proprietary database
> > > companies will tell you they can do it, but their customers will tell
> > > you they can't.
> >
> > Joel Burton suggested the rserv utility. I don't know how well it would
> > work over a wide network.
>
>The point about WANs is that things which work nicely in the lab, on a
>LAN, behave very differently when the communication medium is, like the
>Internet, only fitfully reliable.  You will tend to have events occurring
>in unexpected order, and communications lost, and queues topping over,
>and conflicting entries in different instances which you must somehow
>reconcile after the fact.  Reconciliation by shipping the whole database
>across the WAN is often impractical, particularly when you're trying to
>use it at the same time.
>
>WAN replication is an important part of Zembu's business, and it's hard.
>I would expect the rserv utility (about which I admit I know little) not
>to have been designed for the job.
>
>Nathan Myers
>ncm@zembu.com
>
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Fri, 20 Apr 2001 21:45:52 +0100
Ryan Mahoney <ryan@paymentalliance.net>
Re: Re: Is it possible to mirror the db in Postgres?
Nathan Meyers wrote:

> Does the replication have to be reliable?  Are you equipped to
> reconcile databases that have got out of sync, if not?  Will the
> different labs ever try to update the same existing record, or
> insert conflicting (unique-key) records?
>

(1) Yes, of course.  (2) Willing--yes; equipped--dunno.   (3) Yes,
probably.

Reliable WAN replication is harder.  Most of the proprietary database
companies will tell you they can do it, but their customers will tell
you they can't.

Joel Burton suggested the rserv utility. I don't know how well it would
work over a wide network.

-Tony




Fri, 20 Apr 2001 16:53:43 -0700
"G. Anthony Reina" <reina@nsi.edu>
Re: Is it possible to mirror the db in Postgres?
On Fri, Apr 20, 2001 at 04:53:43PM -0700, G. Anthony Reina wrote:
> Nathan Myers wrote:
> 
> > Does the replication have to be reliable?  Are you equipped to
> > reconcile databases that have got out of sync, when it's not?  
> > Will the different labs ever try to update the same existing 
> > record, or insert conflicting (unique-key) records?
> 
> (1) Yes, of course.  (2) Willing--yes; equipped--dunno.   (3) Yes,
> probably.

Hmm, good luck.  Replication, by itself, is not hard, but it's only
a tiny part of the job.  Most of the job is in handling failures
and conflicts correctly, for some (usually enormous) definition of
"correctly".

> > Reliable WAN replication is harder.  Most of the proprietary database
> > companies will tell you they can do it, but their customers will tell
> > you they can't.
> 
> Joel Burton suggested the rserv utility. I don't know how well it would
> work over a wide network.

The point about WANs is that things which work nicely in the lab, on a 
LAN, behave very differently when the communication medium is, like the 
Internet, only fitfully reliable.  You will tend to have events occurring
in unexpected order, and communications lost, and queues topping over, 
and conflicting entries in different instances which you must somehow 
reconcile after the fact.  Reconciliation by shipping the whole database 
across the WAN is often impractical, particularly when you're trying to
use it at the same time.

WAN replication is an important part of Zembu's business, and it's hard.
I would expect the rserv utility (about which I admit I know little) not
to have been designed for the job.

Nathan Myers
ncm@zembu.com

Fri, 20 Apr 2001 18:19:58 -0700
ncm@zembu.com (Nathan Myers)
Re: Re: Is it possible to mirror the db in Postgres?
> Joel Burton suggested the rserv utility. I don't know how well it would
> work over a wide network.

It should work well over a WAN for what it can do. However, that is
async one-way replication, which was not your initial requirement.

Of course, requirements sometimes adjust in the face of reality ;)

                   - Thomas

Sat, 21 Apr 2001 01:46:22 +0000
Thomas Lockhart <lockhart@alumni.caltech.edu>
Re: Is it possible to mirror the db in Postgres?
Thomas Lockhart wrote:
> 
> > Joel Burton suggested the rserv utility. I don't know how well it would
> > work over a wide network.
> 
> It should work well over a WAN for what it can do. However, that is
> async one-way replication, which was not your initial requirement.
> 
> Of course, requirements sometimes adjust in the face of reality ;)

If it is a low-update mostly-analyze DB then updating on central db and 
then doing async one-way replication from there may be a good strategy.

-------------
Hannu

Sat, 21 Apr 2001 13:44:06 +0200
Hannu Krosing <hannu@tm.ee>
Re: Re: Is it possible to mirror the db in Postgres?