Re: fool-toleranced optimizer - Mailing list pgsql-hackers

Added to TODO:
* Add GUC to issue notice about queries that use unjoined tables


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Kevin Brown wrote:
> Greg Stark wrote:
> > 
> > Kevin Brown <kevin@sysexperts.com> writes:
> > 
> > > Hence, it makes sense to go ahead and run the query, but issue a
> > > warning at the very beginning, e.g. "WARNING: query JOINs tables <list
> > > of tables> without otherwise referencing or making use of those
> > > tables.  This may cause excessively poor performance of the query".
> > 
> > Well the problem with a warning is what if it *is* intentional? It's
> > not ok to fill my logs up with warnings for every time the query is
> > executed. That just forces me to turn off warnings.
> 
> WARNING is probably the wrong level (I wasn't thinking in terms of PG
> logging, though I probably should have been).  What about NOTICE?
> Basically, you want something that will alert the interactive user
> that what they're doing is likely to be stupid, but at the same time
> won't be a burden on the system or the DBA...
> 
> > It would be ok to have an option to block cartesian joins entirely. I might
> > even choose to run with that enabled normally. I can always disable it for
> > queries I know need cartesion joins.
> 
> Which wouldn't work all that well for people who are trying to write
> their software in a reasonably portable fashion, unfortunately.
> However, the number of people who care would now be much smaller.
> 
> > For that matter, I wonder whether it's time to consider an option to
> > disable implicit (ie, pre-ansi join syntax) joins entirely. It seems
> > like lots of shops are likely imposing coding standards that require
> > ansi join syntax anyways. In environments like that you would expect
> > "a CROSS JOIN b" not just "select * from a,b" anyways.
> > 
> > Shops like that might appreciate the ability to enforce a blanket
> > coding standard on that point and get protection from accidental
> > cartesian joins as a side benefit.
> 
> That could be handy, but of course it should default to off, which
> with respect to cross joins would unfortunately wind up benefitting
> only those people who already are potentially aware of the issue and
> care about it (or, at least, those people who have DBAs that care
> about it).
> 
> 
> 
> -- 
> Kevin Brown                          kevin@sysexperts.com
> 
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