BUG #8048: Text Search

The following bug has been logged on the website:

Bug reference:      8048
Logged by:          Luigi
Email address:      luigisag@gmail.com
PostgreSQL version: 9.2.0
Operating system:   Windows 7
Description:        =


I've configured 2 table like this

        CREATE TABLE "User_Full_Text_Search" (
        "Email" varchar(50),
        "UserId" varchar(50),
        "Full_Text_Search" varchar(4096)
        )
        WITH (OIDS=3DFALSE)
        ;
        =

        ALTER TABLE "User_Full_Text_Search" OWNER TO "postgres";
        =

        CREATE INDEX IX_FullText ON "User_Full_Text_Search" USING
gin(to_tsvector('italian', "Full_Text_Search"));
        =

        =

        CREATE TABLE "User_Full_Text_Search_2" (
        "Email" varchar(50),
        "UserId" varchar(50),
        "Full_Text_Search" varchar(4096),
        "tsv" varchar(4096)
        )
        WITH (OIDS=3DFALSE)
        ;
        =

        ALTER TABLE "User_Full_Text_Search_2" OWNER TO "postgres";
        =

        CREATE INDEX IX_FullText_2 ON "User_Full_Text_Search_2" USING
gin("tsv");
    CREATE TRIGGER "tsvectorupdate" BEFORE INSERT OR UPDATE ON
"User_Full_Text_Search_2"
    FOR EACH ROW
    EXECUTE PROCEDURE "tsvector_update_trigger"('tsv', 'pg_catalog.italian',
'Full_Text_Search');

Column Full_Text_Search (table User_Full_Text_Search) is just a single word
or max 2 words separeted by space " " (ex: test tester), and tsv (table
User_Full_Text_Search_2) is populate by materializing column with a
ts_vector of Full_Text_Search.

Now if i perform those 2 queries

    select "UserId","Email" from "User_Full_Text_Search"    =

    where to_tsvector('italian',"Full_Text_Search") @@ to_tsquery('italian',
'test|developer')
    GROUP BY "UserId","Email"
    =

    select "UserId","Email" from "User_Full_Text_Search_2"    =

    where "tsv" @@ to_tsquery('italian', 'test|developer')
    GROUP BY "UserId","Email"

Records on Tables (are same) like 10 milion. =


Execution time of 1st query is 120 seconds (result set like 750.000)
Execution time of 2st query is 270 seconds (result set like 750.000) same
records

I don't understand why a materialized column is more slow than a calculeted
one...