softwareheritage=> explain select ov.* from origin_visit ov INNER JOIN origin o ON o.id = ov.origin WHERE o.url = 'svn://scm.gforge.inria.fr/svnroot/fpg-ipc/' ORDER BY ov.visit DESC LIMIT 1;
                                                   QUERY PLAN                                                   
----------------------------------------------------------------------------------------------------------------
 Limit  (cost=633.57..633.57 rows=1 width=28)
   ->  Sort  (cost=633.57..633.59 rows=7 width=28)
         Sort Key: ov.visit DESC
         ->  Nested Loop  (cost=0.58..633.53 rows=7 width=28)
               ->  Index Scan using origin_url_idx1 on origin o  (cost=0.00..2.02 rows=1 width=8)
                     Index Cond: (url = 'svn://scm.gforge.inria.fr/svnroot/fpg-ipc/'::text)
               ->  Index Scan using origin_visit_pkey on origin_visit ov  (cost=0.58..625.15 rows=637 width=28)
                     Index Cond: (origin = o.id)







For comparison, when removing the join:



softwareheritage=> explain select ov.* from origin_visit ov WHERE ov.origin=162351914 ORDER BY ov.visit DESC LIMIT 1;
                                                 QUERY PLAN                                                  
-------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.58..1.56 rows=1 width=28)
   ->  Index Scan Backward using origin_visit_pkey on origin_visit ov  (cost=0.58..625.15 rows=637 width=28)
         Index Cond: (origin = 162351914)