Difference in query plan

I have a database in a production server (8.1.9) with to schema
containing the sames table same index, same every thing, but with
different data. When I execute a query in one schema, it take much more
time to execute then the other schema. I've issue the query plan and
it's different from one schema to the other. I was assuming that is was
because the contents of the table where different so I've try the query
into a test database into another server (8.3.3) and with both schema, I
get the same query plan and they both work fine

I'm wondering where to start searching to fix this problem

Here is my query:

SELECT bd.component_item_id AS item_id,
rspec('schema_name', bd.component_item_id,
bd.component_control_id) AS control_id,
adjustdate(m.date_due - avior.item_leadtime('schema_name',
bd.item_id, bd.control_id, 0)*7, m.date_due) AS date_due,
bd.item_id AS to_item_id,
bd.control_id AS to_control_id, m.quantity *
totalquantity(bd.quantity,
CASE

WHEN substring(bd.component_item_id, 1, 1) = 'F' THEN bd.size1 + 1

ELSE bd.size1
END,

CASE WHEN substring(bd.component_item_id, 1, 1) = 'F' THEN bd.size2 + 1

ELSE bd.size2

END) / bd.quantity_produce * i.mfg_conv_factor AS quantity
FROM schema_name.mrp m
JOIN schema_name.bom_detail bd
ON bd.item_id = m.item_id
AND bd.control_id = rspec('schema_name', m.item_id, m.control_id)
AND NOT bd.rework,
schema_name.item i
WHERE i.item_id=m.item_id
AND NOT bd.item_supplied
AND bd.component_item_id = 'some value' ;

Production server schema 1 query plan:
QUERY
PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=569.23..634.43 rows=1 width=121) (actual
time=1032.811..1032.811 rows=0 loops=1)
-> Merge Join (cost=569.23..628.36 rows=1 width=127) (actual
time=1032.806..1032.806 rows=0 loops=1)
Merge Cond: (("outer"."?column5?" = "inner".item_id) AND
("outer"."?column6?" = "inner".control_id))
-> Sort (cost=488.89..503.62 rows=5892 width=39) (actual
time=1032.736..1032.736 rows=1 loops=1)
Sort Key: (m.item_id)::text, (rspec('granby'::text,
m.item_id, m.control_id))::text
-> Seq Scan on mrp m (cost=0.00..119.92 rows=5892
width=39) (actual time=0.343..939.462 rows=5892 loops=1)
-> Sort (cost=80.34..80.39 rows=21 width=97) (actual
time=0.059..0.059 rows=0 loops=1)
Sort Key: bd.item_id, bd.control_id
-> Bitmap Heap Scan on bom_detail bd (cost=2.08..79.87
rows=21 width=97) (actual time=0.038..0.038 rows=0 loops=1)
Recheck Cond: ((component_item_id)::text =
'C294301-1'::text)
Filter: ((NOT rework) AND (NOT item_supplied))
-> Bitmap Index Scan on i_bomdetail_component
(cost=0.00..2.08 rows=23 width=0) (actual time=0.031..0.031 rows=0 loops=1)
Index Cond: ((component_item_id)::text =
'C294301-1'::text)
-> Index Scan using pkey_item on item i (cost=0.00..6.01 rows=1
width=31) (never executed)
Index Cond: (i.item_id = ("outer".item_id)::text)
Total runtime: 1034.204 ms
(16 rows)

Production server schema 2 query plan:
QUERY
PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=133.42..793.12 rows=1 width=123) (actual
time=0.130..0.130 rows=0 loops=1)
-> Merge Join (cost=133.42..787.05 rows=1 width=130) (actual
time=0.126..0.126 rows=0 loops=1)
Merge Cond: (("outer".item_id)::text = "inner".item_id)
Join Filter: ("inner".control_id = (rspec('laval'::text,
"outer".item_id, "outer".control_id))::text)
-> Index Scan using pkey_mrp on mrp m (cost=0.00..634.29
rows=7501 width=40) (actual time=0.013..0.013 rows=1 loops=1)
-> Sort (cost=133.42..133.51 rows=34 width=99) (actual
time=0.105..0.105 rows=0 loops=1)
Sort Key: bd.item_id
-> Bitmap Heap Scan on bom_detail bd (cost=2.13..132.56
rows=34 width=99) (actual time=0.099..0.099 rows=0 loops=1)
Recheck Cond: ((component_item_id)::text =
'C294301-1'::text)
Filter: ((NOT rework) AND (NOT item_supplied))
-> Bitmap Index Scan on i_bomdetail_component
(cost=0.00..2.13 rows=37 width=0) (actual time=0.093..0.093 rows=0 loops=1)
Index Cond: ((component_item_id)::text =
'C294301-1'::text)
-> Index Scan using pkey_item on item i (cost=0.00..6.01 rows=1
width=29) (never executed)
Index Cond: (i.item_id = ("outer".item_id)::text)
Total runtime: 0.305 ms
(15 rows)

Test server schema 1 query plan:
QUERY
PLAN
-------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=3.43..367.63 rows=1 width=92) (actual
time=0.248..0.248 rows=0 loops=1)
-> Nested Loop (cost=3.43..360.30 rows=1 width=98) (actual
time=0.243..0.243 rows=0 loops=1)
Join Filter: ((rspec('granby'::text, m.item_id,
m.control_id))::text = bd.control_id)
-> Bitmap Heap Scan on bom_detail bd (cost=3.43..62.59
rows=21 width=74) (actual time=0.240..0.240 rows=0 loops=1)
Recheck Cond: ((component_item_id)::text = 'C294301-1'::text)
Filter: ((NOT rework) AND (NOT item_supplied))
-> Bitmap Index Scan on i_bomdetail_component
(cost=0.00..3.43 rows=23 width=0) (actual time=0.234..0.234 rows=0 loops=1)
Index Cond: ((component_item_id)::text =
'C294301-1'::text)
-> Index Scan using i_mrp_mrp_itm on mrp m (cost=0.00..9.14
rows=19 width=30) (never executed)
Index Cond: ((m.item_id)::text = bd.item_id)
-> Index Scan using pkey_item on item i (cost=0.00..6.27 rows=1
width=24) (never executed)
Index Cond: (i.item_id = bd.item_id)
Total runtime: 0.717 ms
(13 rows)

Test server schema 2 query plan:
QUERY
PLAN
-------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=3.54..381.94 rows=1 width=92) (actual
time=0.273..0.273 rows=0 loops=1)
-> Nested Loop (cost=3.54..374.61 rows=1 width=100) (actual
time=0.269..0.269 rows=0 loops=1)
Join Filter: ((rspec('laval'::text, m.item_id,
m.control_id))::text = bd.control_id)
-> Bitmap Heap Scan on bom_detail bd (cost=3.54..99.80
rows=33 width=75) (actual time=0.265..0.265 rows=0 loops=1)
Recheck Cond: ((component_item_id)::text = 'C294301-1'::text)
Filter: ((NOT rework) AND (NOT item_supplied))
-> Bitmap Index Scan on i_bomdetail_component
(cost=0.00..3.53 rows=36 width=0) (actual time=0.259..0.259 rows=0 loops=1)
Index Cond: ((component_item_id)::text =
'C294301-1'::text)
-> Index Scan using i_mrp_mrp_itm on mrp m (cost=0.00..6.74
rows=6 width=31) (never executed)
Index Cond: ((m.item_id)::text = bd.item_id)
-> Index Scan using pkey_item on item i (cost=0.00..6.28 rows=1
width=21) (never executed)
Index Cond: (i.item_id = bd.item_id)
Total runtime: 0.498 ms
(13 rows)

I'm also wondering why in the production server schema 1 query plan, I'm
getting "outer"."?column5?" instead of "outer"."item_id"

It's also to note that schema 1 contain far less date then schema 2 in
the order of 1 to 4

thanks