On Fri, 26 Jul 2024 at 19:55, Francisco Olarte <folarte@xxxxxxxxxxxxxx> wrote: > " -> Index Scan using > ""cl_student_semester_subject_IX3"" on cl_student_semester_subject p > (cost=0.55..8.57 rows=1 width=60) (actual time=0.033..55.702 > rows=41764 loops=1)" > " Index Cond: (((companycode)::text = '100'::text) > AND ((examheaderfk)::text = > 'BA80952CFF8F4E1C3F9F44B62ED9BF37'::text))" > > Not an explain expert, but if i read correctly an index scan expecting > 1 row recovers 41674, which hints at bad statistics ( or skewed data > distribution and bad luck ) You have correctly identified the reason the poor plan was chosen. If that row estimate was anything higher than 1, that plan wouldn't be picked. If ANALYZE cl_student_semester_subject; does not fix the issue, then increasing the statistics targets with something like: alter table cl_student_semester_subject alter column companycode set (default_statistics_target = 1000); alter table cl_student_semester_subject alter column examheaderfk set (default_statistics_target = 1000); analyze cl_student_semester_subject; (Warning, additional statistics targets can slow down planning a little) or if that does not help and there's some correlation between those columns and/or the values in question, then maybe the following might help get a more accurate estimate: create statistics on companycode, examheaderfk from cl_student_semester_subject; analyze cl_student_semester_subject; David
