Re: Query length restriction in v3 protocol?

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Hi Mark,

Mark Lewis schrieb am 10.05.2006 01:19:
> This doesn't address your immediate problem, but the primary reason that
> Hibernate joined-subclass performance stinks on PG is because the query
> planner does a very poor job of optimizing outer joins, which Hibernate
> uses extensively in its polymorphic queries for joined-subclass.
>
> One of the features coming in the 8.2 PG release is greatly improved
> outer join planning, so you should be able to go back to joined-subclass
> polymorphism, which is the easiest to work with in code anyway.

Hm. "Easy" depends on the viewpoint. Granted, the table per concrete
class is *very* easy to understand and insert/update performance is
great. So far for the advantages. Drawback are the huge SQL queries in
case of implicit polymorphism and the lack of constraints, which would
be the reason to go back to normalized mapping after PG8.2.
The outer join planning enhancements is in CVS already? If, I would give
it a try... ;-)

> There might also be a workaround you could use to get acceptable
> performance out of joined-subclass using current versions of PG (Caveat:
> I haven't tried this).  When current versions of PG give up on
> optimizing outer joins, they fall back to processing the joins in the
> order listed in the SQL query.  Depending on the order the joins are
> listed, this could result in really bad performance.

Hibernate always starts with the superclass down to the subclasses, so I
think I cannot do something against it... (except for the ordering
inside one level of inheritance inside one superclass).

thanks already for the great 8.2 announcement, it lifts my hope... :-)

- --
Mit freundlichen Gruessen / Regards
Patric Bechtel, IPCON Informationssysteme OHG
Kontakt: http://www.ipcon.de/kontakt.php
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