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 ?


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 |
"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    |
   "pk_string_stringid" primary key, btree (stringid)


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

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

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

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