On 01/05/11 11:53, Greg Stark wrote:
On Sat, Apr 30, 2011 at 9:21 PM, Tom Lane<t...@sss.pgh.pa.us> wrote:
- it would require a query in which
every relation is linked to every other relation by a join clause.
But that *can* happen (remember that clauses generated by transitive
equality do count).
It sounds like you're describing precisely a "star schema" join which
isn't an uncommon design pattern at all.
Nice example here:
http://archives.postgresql.org/pgsql-bugs/2011-04/msg00100.php
Strictly only a 'star-like' query as the foreign key references go the
opposite way from a true star. However it illustrates the planner memory
growth well (1.1G on 32-bit 1.7G on 64-bit systems).
A point I didn't mention is that the memory use is quite dependent on
the choice of "word" values for the "AND keyword = 'word'" clause - the
text example had 6 all the same. Setting them all different (even after
adjusting the data so the there *was* a number of matching rows to find)
resulted in significantly less memory consumed (I can dig up some
examples if it might be interesting).
Cheers
Mark
