Performance issue 6.5 versus 7.0

I made an upgrade these days to 7.0 for one machine. I noticed
a better performance in general. Congratulation.

I have one problem with a query which is joining 3 tables and which
is returning one record. In 6.5.3 the results came up immediately.
In 7.0 the same query takes about 5 seconds. Here the explain
results  (Same database with the same amount of records and
same indexes, vacuum was executed before)

Query under 6.5.3:
------------------
EXPLAIN
SELECT MailingListe_Id, MailingStatus, AbschlussDatum, Anschrift.Anzeige,
       Anschrift.Postfach, Anschrift.Strasse, Anschrift.Plz, Anschrift.Ort,
       Anschrift.TelDirekt, Person.Person_Id, Person.Name, Person.Vorname,
       Person.Anzeige
  FROM Anschrift, Person, MailingListe
 WHERE Person.Person_Id = MailingListe.Person_Id
   AND Anschrift.Anschrift_Id = MailingListe.Anschrift_Id
   AND MailingListe_Id = 2104;

 NOTICE:  QUERY PLAN:
Nested Loop  (cost=53.30 rows=23 width=513)
  ->  Nested Loop  (cost=6.15 rows=23 width=232)
        ->  Index Scan using mailingliste_id_ix on mailingliste  (cost=2.05 rows=2 width=36)
        ->  Index Scan using person_id_ix on person  (cost=2.05 rows=24051 width=196)
  ->  Index Scan using anschrift_id_ix on anschrift  (cost=2.05 rows=13661 width=281)

result is returned immediately on a Pentium II

Query under 7.0
---------------
Same query:
NOTICE:  QUERY PLAN:
Merge Join  (cost=5991.20..6395.18 rows=1988449 width=136)
  ->  Sort  (cost=2984.98..2984.98 rows=8268 width=96)
        ->  Merge Join  (cost=2037.87..2209.39 rows=8268 width=96)
              ->  Sort  (cost=1993.14..1993.14 rows=13661 width=76)
                    ->  Seq Scan on anschrift  (cost=0.00..728.61 rows=13661 width=76)
              ->  Sort  (cost=44.73..44.73 rows=61 width=20)
                    ->  Index Scan using mailingliste_id_ix on mailingliste  (cost=0.00..42.94 rows=61 width=20)
  ->  Sort  (cost=3006.22..3006.22 rows=24051 width=40)
        ->  Seq Scan on person  (cost=0.00..896.51 rows=24051 width=40)

Select takes about 5 seconds on Pentium III/550 Mhz

When I do a select * From those tables I get the same query plan
under 6.5.3 and a different query plan und 7.0;

NOTICE:  QUERY PLAN (7.0)
Merge Join  (cost=4201.39..8326.56 rows=1988449 width=513)
  ->  Index Scan using person_id_ix on person  (cost=0.00..3721.19 rows=24051 width=196)
  ->  Sort  (cost=4201.39..4201.39 rows=8268 width=317)
        ->  Merge Join  (cost=44.73..2941.79 rows=8268 width=317)
              ->  Index Scan using anschrift_id_ix on anschrift  (cost=0.00..2725.55 rows=13661 width=281)
              ->  Sort  (cost=44.73..44.73 rows=61 width=36)
                    ->  Index Scan using mailingliste_id_ix on mailingliste  (cost=0.00..42.94 rows=61 width=36)



Is there a way to force 7.0 using the defined indexes? Thanks
for your help.

Greetings Herbie
--
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Herbert Liechti                     E-Mail: Herbert.Liechti@thinx.ch
ThinX networked business services        Stahlrain 10, CH-5200 Brugg
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