Poor Performance on Postgres 8.0

Hi Folks ,

I am running this query on postgres 8 beta version and it is not
using the right index, where as if i run the same query on postgres 7.4
version it uses the right index . Here are the explain analyze output
for both the versions. can anyone explain this ?

tks.

tables: attribute table has 200k records, string table has 190 records

\d common.attribute
Table "common.attribute"
Column | Type |
Modifiers
----------------+-----------------------------+-------------------------------------------------------
attributeid | integer | not null default
nextval('COMMON.ATTRIBUTESEQ'::text)
fknamestringid | integer | not null
stringvalue | text |
integervalue | integer |
numericvalue | numeric(14,2) |
datevalue | timestamp without time zone |
booleanvalue | boolean |
bigstringvalue | text |
Indexes:
"pk_attribute_attributeid" primary key, btree (attributeid)
"uk_attribute_fkstringid_stringvalue_integervalue_numericvalue_d"
unique, btree (fknamestringid, stringvalue, integervalue, numericvalue,
datevalue)
"idx_attribute_fknamestringid" btree (fknamestringid)
Foreign-key constraints:
"fk_attribute_string" FOREIGN KEY (fknamestringid) REFERENCES
common.string(stringid)

\d common.string
Table "common.string"
Column | Type | Modifiers
----------+---------+----------------------------------------------------
stringid | integer | not null default nextval('COMMON.STRINGSEQ'::text)
value | text |
Indexes:
"pk_string_stringid" primary key, btree (stringid)

Query

select attribute0_.attributeid as attribut1_, attribute0_.stringvalue as
stringva2_,
attribute0_.bigStringvalue as bigStrin3_, attribute0_.integervalue
as integerv4_,
attribute0_.numericvalue as numericv5_, attribute0_.datevalue as
datevalue,
attribute0_.booleanvalue as booleanv7_, attribute0_.fknamestringid
as fknamest8_
from common.attribute attribute0_, common.string text1_
where (text1_.value='squareFeet' and
attribute0_.fknamestringid=text1_.stringid)
and (numericValue='775.0')

Explain Analyze from 7.4

QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=0.00..501.96 rows=1 width=100) (actual
time=127.420..135.914 rows=1 loops=1)
-> Seq Scan on string text1_ (cost=0.00..12.31 rows=2 width=4)
(actual time=68.421..68.466 rows=1 loops=1)
Filter: (value = 'squareFeet'::text)
-> Index Scan using idx_attribute_fknamestringid on attribute
attribute0_ (cost=0.00..244.81 rows=1 width=100) (actual
time=58.963..67.406 rows=1 loops=1)
Index Cond: (attribute0_.fknamestringid = "outer".stringid)
Filter: (numericvalue = 775.0)
Total runtime: 136.056 ms

Explain Analyze from 8 beta

QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=0.00..5440.85 rows=1 width=109) (actual
time=27.313..440.469 rows=1 loops=1)
-> Seq Scan on attribute attribute0_ (cost=0.00..5437.82 rows=1
width=109) (actual time=26.987..440.053 rows=2 loops=1)
Filter: (numericvalue = 775.0)
-> Index Scan using pk_string_stringid on string text1_
(cost=0.00..3.02 rows=1 width=4) (actual time=0.169..0.172 rows=0 loops=2)
Index Cond: ("outer".fknamestringid = text1_.stringid)
Filter: (value = 'squareFeet'::text)
Total runtime: 440.648 ms