Re: Deprecating RULES

On Fri, Oct 19, 2012 at 5:03 PM, Josh Berkus <josh@agliodbs.com> wrote:
>> That's a pretty neat one-liner.  However... in my view, the real cost
>> of rules is that they are hard to support as we add new features to
>> SQL.  I believe we already decided to punt on making them work with
>> CTEs... and maybe one other case?  I don't really remember the details
>> any more, but presumably this will come up again with MERGE, and
>> perhaps other cases...
>
> Unless the easiest way to implement MERGE is to extend RULEs.

The problems with MERGE are mostly around concurrency, as far as I can
tell.  I can't see why RULEs would have anything to do with it -
except that I don't see how MERGE can sanely support rules, and even
if we find a way to make it do that, anyone already using RULEs will
need to adjust them to support MERGE.  I'm not sure I have a horribly
well-thought-out position on the underlying issue here - I'm kind of
vacillating back and forth - but I do think one of the problems with
RULEs is that they are too tied to particular command names.  Adding
any new commands that can select or modify data - be it MERGE, UPSERT,
or whatever - is going to cause trouble both for implementors and for
people relying on the feature.

> For example, imagine you have a series of CSV FDWs which relate to
> segments of a postgres log.  You want to query them like they were one
> table.  How would you use triggers to do that?

You wouldn't.  You'd use a view, which of course is the only kind of
rules that are not being proposed for deprecation.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company