Query taking long time

Hello to everybody and thanks in advance to take a look to this message.
I'm new in this list and with PostgreSQL.
My queries are taking too much time to complete and I don't know what to do right now. I think I'm providing all  the
inforequired for you to help me. If you need extra info please tell me. 

I am using DQL included in the last version of symfony2 (2.4.2). This is the query, formed by DQL, but coppied-pasted
tothe psql client (9.1.11, server 8.3.8) 

explain analyze SELECT e0_.id AS id0, e0_.name AS name1, e0_.qualifier AS qualifier2, e0_."tagMethod" AS tagmethod3,
e0_.curationAS curation4, e0_.created AS created5, e0_.updated AS updated6, d1_.id AS id7, d1_.kind AS kind8, d1_.uid
ASuid9, d1_."sentenceId" AS sentenceid10, d1_.text AS text11, d1_.hepval AS hepval12, d1_.cardval AS cardval13,
d1_.nephvalAS nephval14, d1_.phosval AS phosval15, d1_."patternCount" AS patterncount16, d1_."ruleScore" AS
rulescore17,d1_."hepTermNormScore" AS heptermnormscore18, d1_."hepTermVarScore" AS heptermvarscore19, d1_.created AS
created20,d1_.updated AS updated21, e0_.document_id AS document_id22 FROM Entity2Document e0_ INNER JOIN documentold
d1_ON e0_.document_id = d1_.id WHERE e0_.name ='ranitidine' AND e0_.qualifier = 'CompoundDict' AND d1_.hepval IS NOT
NULLORDER BY d1_.hepval DESC limit 10; 


limtox=> \d+ documentold;
                               Table "public.documentold"
      Column      |              Type              | Modifiers | Storage  | Description
------------------+--------------------------------+-----------+----------+-------------
 id               | integer                        | not null  | plain    |
 kind             | character varying(255)         | not null  | extended |
 uid              | character varying(255)         | not null  | extended |
 sentenceId       | character varying(255)         | not null  | extended |
 text             | text                           | not null  | extended |
 hepval           | double precision               |           | plain    |
 created          | timestamp(0) without time zone | not null  | plain    |
 updated          | timestamp(0) without time zone |           | plain    |
 cardval          | double precision               |           | plain    |
 nephval          | double precision               |           | plain    |
 phosval          | double precision               |           | plain    |
 patternCount     | double precision               |           | plain    |
 ruleScore        | double precision               |           | plain    |
 hepTermNormScore | double precision               |           | plain    |
 hepTermVarScore  | double precision               |           | plain    |
Indexes:
    "DocumentOLD_pkey" PRIMARY KEY, btree (id)
    "document_cardval_index" btree (cardval)
    "document_heptermnorm_index" btree ("hepTermNormScore" DESC NULLS LAST)
    "document_heptermvar_index" btree ("hepTermVarScore" DESC NULLS LAST)
    "document_hepval_index" btree (hepval DESC NULLS LAST)
    "document_kind_index" btree (kind)
    "document_nephval_index" btree (nephval DESC NULLS LAST)
    "document_patterncount_index" btree ("patternCount" DESC NULLS LAST)
    "document_phosval_index" btree (phosval DESC NULLS LAST)
    "document_rulescore_index" btree ("ruleScore" DESC NULLS LAST)
    "document_sentenceid_index" btree ("sentenceId")
    "document_uid_index" btree (uid)
Referenced by:
    TABLE "hepkeywordtermnorm2document" CONSTRAINT "fk_1c19bcd0c33f7837" FOREIGN KEY (document_id) REFERENCES
documentold(id)
    TABLE "cytochrome2document" CONSTRAINT "fk_21f7636fc33f7837" FOREIGN KEY (document_id) REFERENCES documentold(id)
    TABLE "hepkeywordtermvariant2document" CONSTRAINT "fk_a316e36bc33f7837" FOREIGN KEY (document_id) REFERENCES
documentold(id)
    TABLE "entity2document" CONSTRAINT "fk_a6020c0dc33f7837" FOREIGN KEY (document_id) REFERENCES documentold(id)
    TABLE "specie2document" CONSTRAINT "fk_b6e551c8c33f7837" FOREIGN KEY (document_id) REFERENCES documentold(id)
Has OIDs: no




limtox=> \d+ entity2document;                                     Table "public.entity2document"   Column    |
   Type              |            Modifiers            | Storage  | Description
-------------+--------------------------------+---------------------------------+----------+-------------id          |
integer                       | not null                        | plain    |  
 document_id | integer                        |                                 | plain    |
 name        | character varying(255)         | not null                        | extended |
 qualifier   | character varying(255)         | not null                        | extended |
 tagMethod   | character varying(255)         | default NULL::character varying | extended |
 created     | timestamp(0) without time zone | not null                        | plain    |
 updated     | timestamp(0) without time zone |                                 | plain    |
 curation    | integer                        |                                 | plain    |
Indexes:
    "Entity2Document_pkey" PRIMARY KEY, btree (id)
    "entity2Document_name_index" btree (name)
    "entity2document_name_qualifier_index" btree (name, qualifier)
    "idx_a6020c0dc33f7837" btree (document_id)
    "qualifier_index" btree (qualifier)
Foreign-key constraints:
    "fk_a6020c0dc33f7837" FOREIGN KEY (document_id) REFERENCES documentold(id)
Has OIDs: no






Table metadata:
    documentold: 124.515.592 of rows. It has several columns with a large proportion of NULLs(updated, patternCount,
ruleScore,hepTermNormScore, hepTermVarScore) 
    entity2document: 93.785.968 of rows. It has two columns with a large proportion of NULLs (updated, curation)

None of the tables receive updates or deletes regularly


                                                                                QUERY PLAN
                                                  

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=387929.02..387929.05 rows=10 width=313) (actual time=55980.472..55980.476 rows=10 loops=1)
   ->  Sort  (cost=387929.02..387966.75 rows=15090 width=313) (actual time=55980.471..55980.473 rows=10 loops=1)
         Sort Key: d1_.hepval
         Sort Method:  top-N heapsort  Memory: 28kB
         ->  Nested Loop  (cost=469.14..387602.93 rows=15090 width=313) (actual time=96.716..55974.004 rows=2774
loops=1)
               ->  Bitmap Heap Scan on entity2document e0_  (cost=469.14..54851.25 rows=15090 width=59) (actual
time=51.299..8452.592rows=2774 loops=1) 
                     Recheck Cond: (((name)::text = 'Cimetidine'::text) AND ((qualifier)::text = 'CompoundDict'::text))
                     ->  Bitmap Index Scan on entity2document_name_qualifier_index  (cost=0.00..465.36 rows=15090
width=0)(actual time=36.467..36.467 rows=2774 loops=1) 
                           Index Cond: (((name)::text = 'Cimetidine'::text) AND ((qualifier)::text =
'CompoundDict'::text))
               ->  Index Scan using "DocumentOLD_pkey" on documentold d1_  (cost=0.00..22.04 rows=1 width=254) (actual
time=17.113..17.129rows=1 loops=2774) 
                     Index Cond: (d1_.id = e0_.document_id)
                     Filter: (d1_.hepval IS NOT NULL)
 Total runtime: 55980.554 ms
(13 rows)

 version
-----------------------------------------------------------------------------------------------------
 PostgreSQL 8.3.8 on x86_64-pc-linux-gnu, compiled by GCC gcc-4.4.real (Ubuntu 10.4.1-3ubuntu3) 10.4.1

 This query has been always slow. It's fast only when it's cached. Vacuum and analyze have been done manually very
recently




 SELECT name, current_setting(name), source
  FROM pg_settings
  WHERE source NOT IN ('default', 'override');

             name            |  current_setting   |        source
----------------------------+--------------------+----------------------
 client_encoding            | UTF8               | client
 DateStyle                  | ISO, DMY           | configuration file
 default_text_search_config | pg_catalog.spanish | configuration file
 effective_cache_size       | 7500MB             | configuration file
 lc_messages                | es_ES.UTF-8        | configuration file
 lc_monetary                | es_ES.UTF-8        | configuration file
 lc_numeric                 | C                  | configuration file
 lc_time                    | es_ES.UTF-8        | configuration file
 listen_addresses           | *                  | configuration file
 log_line_prefix            | %t                 | configuration file
 log_timezone               | localtime          | command line
 maintenance_work_mem       | 2000MB             | configuration file
 max_connections            | 100                | configuration file
 max_fsm_pages              | 63217760           | configuration file
 max_stack_depth            | 2MB                | environment variable
 port                       | 5432               | configuration file
 shared_buffers             | 1500MB             | configuration file
 ssl                        | on                 | configuration file
 tcp_keepalives_count       | 9                  | configuration file
 tcp_keepalives_idle        | 7200               | configuration file
 tcp_keepalives_interval    | 75                 | configuration file
 TimeZone                   | localtime          | command line
 timezone_abbreviations     | Default            | command line
 work_mem                   | 50MB               | configuration file

 Setting the work_mem to 3000MB doesn't change anything...

 Everything seems good to me but the Recheck Cond, because of the large ammount of rows, is slowing the query too much.
Ihave read that is not a good point to try to get rid of recheck cond (maybe even not possible, I don't know, I'm new
toPostgreSQL). I'd like to know what I am doing wrong and how can I solve it... 

 Any help please?

 Thank you very much,

 Andrés
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