Re: optimization downgrade perfomance?

eVl <evl.evl@gmail.com> writes:
>> You tell us --- let's see EXPLAIN ANALYZE results for both cases.

> Here EXPLAIN ANALYZE results for both queries attached.

The problem seems to be that the is_uaix() function is really slow
(somewhere around 4 msec per call it looks like).  Look at the
first scan over stats:

  ->  Index Scan using cdate_cluster on stats s  (cost=0.00..201.51 rows=6 width=25) (actual time=5.231..2165.145
rows=418loops=1) 
        Index Cond: (cdate = '2005-09-01'::date)
        Filter: ((fromip << '192.168.0.0/16'::inet) AND (NOT (toip << '192.168.0.0/16'::inet)) AND (CASE is_uaix(toip)
WHENtrue THEN 'local'::text ELSE 'global'::text END = 'global'::text)) 

versus

  ->  Index Scan using cdate_cluster on stats s  (cost=0.00..165.94 rows=1186 width=25) (actual time=0.131..43.258
rows=578loops=1) 
        Index Cond: (cdate = '2005-09-01'::date)
        Filter: ((fromip << '192.168.0.0/16'::inet) AND (NOT (toip << '192.168.0.0/16'::inet)))

The 578 evaluations of the CASE are adding over 2100msec.  There's
another 1600 evaluations needed in the other arm of the UNION...

Better look at exactly what is_uaix() is doing, because the CASE structure
is surely not that slow.

            regards, tom lane