Date: Wed, 8 Aug 2007 15:15:52 +0200
From: Enrico Weigelt <weigelt@metux.de>
To: pgsql-sql <pgsql-sql@postgresql.org>
Subject: Re: Database synchronization
Message-ID: <20070808131552.GD27936@nibiru.local>
Reply-To: weigelt@metux.de
References: <20070724143737.GA25948@apartia.fr>
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* Jyoti Seth <jyotiseth2001@gmail.com> wrote:

Hi,

if you can live with some seconds lag, you can use an separate
transfer process which looks at the source of your prices and 
and updates the second DB if some price changes. 

Depending on how often prices change, there're two good options:

a) add an timestamp field to the original price table, which is 
   maintained by an after-trigger. The transfer regularily 
   (ie. every few secs) fetches all those records which have 
   been changed since last poll (via the new timestamp field).

b) create an new table for an journal of the price changes.
   this journal is filled by rules on the original table and 
   contains exactly what's needed to reproduce the price changes
   in the other DB. The transfer process regularily fetches
   the journal and rolls it out in the second DB.
   
I've implemented the method b) in an realtime stock (FOREX) 
trading applications where trading automatically robots execute 
transactions on the customer's broker accounts on signals 
provided by an team of profession traders. (the client can 
subscribe to several trading signal channels and define in 
which quantities transactions should be performed from which
channels should be executed on their broker accounts and the
broking platform does all the time critical work). The robots
work entirely on separate databases (on separate hosts),
several transfer processes feed in robot commands and fetch
back results to the primary database. So time critical things
are separated to own servers. It works quite fine :)


cu
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