On Wed, Nov 29, 2006 at 04:03:43PM +0100, Csaba Nagy wrote:
> So it all boils down on how the data is transferred, text or binary, and
> strictly typed or not...

The data is transferred as standard libpq; in principle, anything you
can put in a regular SQL statement you oughta be able to get through
Slony.  There are some issues with datatype in/out conversions that
occasionally bite one, note.  That would be where the tricks are.  

As for the Oracle side, here is the central problem: you need to be
very careful with visibility rules, and very careful in understanding
exactly what you can capture in a given sync set.  The details of
this are one of the really clever parts in Slony-I (thanks to Jan),
and I don't know to what extent a similar approach could be produced
in Oracle (I'm not saying it can't be; just that I don't know Oracle
well enough to say anything meaningful about it one way or the
other).

My suggestion is to look at the SPI code, the sync code, and the
original concept/design doc all together, to get a clear idea of how
it's supposed to work.  If you do that, you can probably see where
the hinky bits are, and then you can explore further the extent to
which it's worth doing.

I suspect that, from a community point of view, the design of such a
beast would need a few additional things to be a candidate for
inclusion with Slony.  Off the top of my head, I'd say that at least
a proposal for how to go the other way (from Postgres to Oracle)
would be very nice, the option to turn it off at build time (or, more
likely, an --enable-oracle-compat or something), and some outline of
what limitations the additional support would impose (I bet there are
datatypes that _will_ have problems, and we'd need to catch those
somehow).  The goal of all of that is to avoid having pieces of the
code that are very "bare metal".  Slony has the number of safeguards
it does precisely because we concluded previous systems were too easy
to use as devices for self-inflicted injury; and we still get things
that people do to themselves where the docs say DON'T DO THIS ON PAIN
OF FOOT SHOT.

A

-- 
Andrew Sullivan  | ajs at crankycanuck.ca
A certain description of men are for getting out of debt, yet are
against all taxes for raising money to pay it off.
		--Alexander Hamilton