Re: Comparison of PGSQL and DB2

From: Robert Treat <xzilla(at)users(dot)sourceforge(dot)net>
To: josh(at)postgresql(dot)org
Cc: Shashank Joshi <shashyajoshi(at)yahoo(dot)com>,pgsql-advocacy(at)postgresql(dot)org
Subject: Re: Comparison of PGSQL and DB2
Date: 2004-03-11 18:39:50
Message-ID: 1079030391.2753.601.camel@camel
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On Tue, 2004-03-09 at 13:22, Josh Berkus wrote:
> Shashank:
> What follows is my reply to IBM's 2-year-old feature comparison of PostgreSQL
> and DB2. Each of the entries is an item that DB2 has and claims that
> PostgreSQL does not. I've put my replies to these claims.
> > Isolation Levels
> > (Support all four ANSI isolation levels (UR, CS, RS, RR).)
> I'm not sure about this one; I suspect that we do, however, since MVCC,
> invented for the Postgres Project, has become a standard for transaction
> isolation in the database industry.

Not exactly sure which acronyms above correspond to which levels (as I
know them by different names apparently) but we support Read Committed
and Serializable levels, which are by far the most common of the two
AFAIK. The others as I know them are Read Uncommitted aka phantom reads,
and Repeatable Read, which we do not support. Of course we also supply a
extensive locking methods for further control.

More info on our isolation levels can be found at

> > Federated Database Support
> > (Ability to allow applications to access & perform JOIN operations on
> multiple disparate databases.)
> This is a feature which we do not have because it violates the ANSI SQL
> Specification.

Perhaps worth a mention that using dblink, you can actually make
functionality similar to this. I have recently been experimenting with
using views calling dblink functions to create "local tables" that
really live in a separate database on a completely separate machine. I
don't know if I would recommend the technique but I think the
capabilities are there.

Robert Treat
Build A Brighter Lamp :: Linux Apache {middleware} PostgreSQL

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