[PERFORM] expression (functional) index use in joins

[Roger Ging]

I just installed v7.4 and restored a database from v7.3.4.  I have an 
index based on a function that the planner is using on the old version, 
but doing seq scans on left joins in the new version.  I have run 
analyze on the table post restore. the query returns in less than 1 
second on version 7.3.4 and takes over 10 seconds on version 7.4.  Any 
help will be appreciated.

Roger Ging

Query:

SELECT L.row_id FROM music.logfile L LEFT JOIN music.program P ON
music.fn_mri_id_no_program(P.mri_id_no) = L.program_id
WHERE  L.station = UPPER('kabc')::VARCHAR
AND L.air_date = '04/12/2002'::TIMESTAMP
AND P.cutoff_date IS NULL
ORDER BY L.chron_start,L.chron_end;
planner results on 7.4:

 Sort  (cost=17595.99..17608.23 rows=4894 width=12)
   Sort Key: l.chron_start, l.chron_end
   ->  Merge Left Join  (cost=17135.92..17296.07 rows=4894 width=12)
         Merge Cond: ("outer"."?column5?" = "inner"."?column3?")
         Filter: ("inner".cutoff_date IS NULL)
         ->  Sort  (cost=1681.69..1682.73 rows=414 width=21)
               Sort Key: (l.program_id)::text
               ->  Index Scan using idx_logfile_station_air_date on 
logfile l  (cost=0.00..1663.70 rows=414 width=21)
                     Index Cond: (((station)::text = 'KABC'::text) AND 
(air_date = '2002-04-12 00:00:00'::timestamp without time zone))
         ->  Sort  (cost=15454.22..15465.06 rows=4335 width=20)
               Sort Key: (music.fn_mri_id_no_program(p.mri_id_no))::text
               ->  Seq Scan on program p  (cost=0.00..15192.35 
rows=4335 width=20)

planner results on 7.3.4:

 Sort  (cost=55765.51..55768.33 rows=1127 width=41)
   Sort Key: l.chron_start, l.chron_end
   ->  Nested Loop  (cost=0.00..55708.36 rows=1127 width=41)
         Filter: ("inner".cutoff_date IS NULL)
         ->  Index Scan using idx_logfile_station_air_date on logfile l 
 (cost=0.00..71.34 rows=17 width=21)
               Index Cond: ((station = 'KABC'::character varying) AND 
(air_date = '2002-04-12 00:00:00'::timestamp without time zone))
         ->  Index Scan using idx_program_mri_id_no_program on program 
p  (cost=0.00..3209.16 rows=870 width=20)
               Index Cond: (music.fn_mri_id_no_program(p.mri_id_no) = 
"outer".program_id)

table "Program" details:

     Column     |            Type             | Modifiers
----------------+-----------------------------+-----------
 record_id      | integer                     |
 title          | character varying(40)       |
 mri_id_no      | character varying(8)        |
 ascap_cat      | character varying(1)        |
 ascap_mult     | numeric(5,3)                |
 ascap_prod     | character varying(10)       |
 npa_ind        | character varying(3)        |
 non_inc_in     | character varying(1)        |
 as_pr_su       | character varying(1)        |
 as_1st_run     | character varying(1)        |
 as_cue_st      | character varying(1)        |
 bmi_cat        | character varying(2)        |
 bmi_mult       | numeric(6,2)                |
 bmi_prod       | character varying(7)        |
 year           | integer                     |
 prog_type      | character varying(1)        |
 total_ep       | integer                     |
 last_epis      | character varying(3)        |
 syndicator     | character varying(6)        |
 station        | character varying(4)        |
 syn_loc        | character varying(1)        |
 spdb_ver       | character varying(4)        |
 as_filed       | character varying(4)        |
 bmidb_ver      | character varying(4)        |
 cutoff_date    | timestamp without time zone |
 effective_date | timestamp without time zone |
 program_id     | character varying(5)        |
Indexes:
    "idx_program_mri_id_no" btree (mri_id_no)
    "idx_program_mri_id_no_program" btree 
(music.fn_mri_id_no_program(mri_id_no))
    "idx_program_program_id" btree (program_id)
    "program_mri_id_no" btree (mri_id_no)
    "program_oid" btree (oid)

---------------------------(end of broadcast)---------------------------
TIP 9: the planner will ignore your desire to choose an index scan if your
     joining column's datatypes do not match