start time very high - Mailing list pgsql-performance

hi,

I have two computers, one laptop (1.5 GHz, 512 Mb RAM, 1 disk 4200)
and one big Sun (8Gb RAM, 2 disks SCSI).

On my laptop, I have this EXPLAIN ANALYZE

Sort  (cost=7.56..7.56 rows=1 width=28) (actual time=0.187..0.187
rows=0 loops=1)
   Sort Key: evolution, indx
   ->  Index Scan using index_xdb_child on xdb_child c1
(cost=0.00..7.55 rows=1 width=28) (actual time=0.045..0.045 rows=0 loops=1)
         Index Cond: ((doc_id = 100) AND (ele_id = 1) AND (isremoved = 0))
         Filter: (evolution = (subplan))
         SubPlan
           ->  Aggregate  (cost=3.78..3.78 rows=1 width=4) (never executed)
                 ->  Index Scan using index_xdb_child on xdb_child c2
(cost=0.00..3.77 rows=1 width=4) (never executed)
                       Index Cond: ((doc_id = 100) AND (ele_id = 1))
                       Filter: ((evolution <= 0) AND (child_id = $0) AND
(child_class = $1))
 Total runtime: 0.469 ms
(11 rows)


and on the SUN:

"Sort  (cost=7.56..7.56 rows=1 width=28) (actual time=26.335..26.335
rows=0 loops=1)"
"  Sort Key: evolution, indx"
"  ->  Index Scan using index_xdb_child on xdb_child c1
(cost=0.00..7.55 rows=1 width=28) (actual time=26.121..26.121 rows=0
loops=1)"
"        Index Cond: ((doc_id = 100) AND (ele_id = 1) AND (isremoved = 0))"
"        Filter: (evolution = (subplan))"
"        SubPlan"
"          ->  Aggregate  (cost=3.78..3.78 rows=1 width=4) (never executed)"
"                ->  Index Scan using index_xdb_child on xdb_child c2
(cost=0.00..3.77 rows=1 width=4) (never executed)"
"                      Index Cond: ((doc_id = 100) AND (ele_id = 1))"
"                      Filter: ((evolution <= 0) AND (child_id = $0)
AND (child_class = $1))"
"Total runtime: 26.646 ms"




so the request run in 26.646 ms on the Sun and 0.469ms on my laptop :-(
the database are the same, vacuumed and I think the Postgres (8.0.3)
are well configured.
The Sun has two disks and use the TABLESPACE to have index on one disk
and data's on the other disk.
It seems that the cost of the first sort is very high on the Sun.
How is it possible ?

the request:

explain analyze select * from XDB_CHILD c1
                                where c1.doc_id = 100
                                and c1.ele_id = 1
                                and c1.isremoved = 0
                                and c1.evolution = (select max(evolution)
                                                        from XDB_CHILD c2
                                                        where c2.doc_id=100
                                                        and c2.ele_id=1
                                                        and c2.evolution<=0
                                                        and
c2.child_id=c1.child_id
                                                        and
c2.child_class=c1.child_class) ORDER BY c1.evolution, c1.indx

--
Jean-Max Reymond
CKR Solutions Open Source
Nice France
http://www.ckr-solutions.com