functional index and the planner (v7.4) - Mailing list pgsql-sql

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..17296.07rows=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..55708.36rows=1127 width=41)         Filter: ("inner".cutoff_date IS NULL)         ->  Index Scan using
idx_logfile_station_air_dateon logfile l  (cost=0.00..71.34 rows=17 width=21)               Index Cond: ((station =
'KABC'::charactervarying) AND 
 
(air_date = '2002-04-12 00:00:00'::timestamp without time zone))         ->  Index Scan using
idx_program_mri_id_no_programon 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        |
charactervarying(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        |
charactervarying(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       |
charactervarying(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     |
charactervarying(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)