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Some thoughts on replication

From: Dirk Heinrichs <heini(at)chaos(dot)tng(dot)oche(dot)de>
To: pgsql-admin(at)postgresql(dot)org
Subject: Some thoughts on replication
Date: 2001-01-25 17:45:11
Message-ID: 01012518451100.12641@linux (view raw, whole thread or download thread mbox)
Lists: pgsql-admin
Hi folks,

Maybe this belongs to the developers mailing list, but I'm not subscribed to 
that list, so I post it here.

I've read through todo list on the website, especially the planned 
replication feature. It seems to me that implementing replication into 
postgresql is a rather hard and longterm task.

I want to show two possible alternatives, used in a real world application (a 
billing system based on Informix) I was involved in a few years ago.

In our case we didn't need (or want) to replicate the whole database, but 
only a few tables. The first thing was to use synonym tables. In Infomix one 
can just type something like

create synonym mysynonym for table mytable:somedb(at)somehost;

where the somedb and somehost values are optional. It was then possible to 
work on the synonym as if it where a normal table.

Later, we also did table replication based on triggers, a daemon and a 
configuration table. The tables which had to be replicated where entered in 
the config table, together with their destination. Then a little script was 
used to setup the apprpriate insert, update and delete triggers for those 
tables. When one of the triggers fired, the daemon contacted its friend on 
the other host and did the same action on the remote database. I think there 
was also a timestamp in the config table which had to be updated. I don't 
know more details anymore, but that was roughly the concept.

Maybe one of those two (or both) is easier and faster to realise than 
database replication.

Any comments?




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