Re-Reason of Slowness of Query - Mailing list pgsql-performance

Thanks Chetan, After my Lunch Break, I tried the below steps :

My original query was :
explain analyze select distinct(p.crawled_page_id) from page_content p , clause2  c where p.crawled_page_id != c.source_id

which hangs because it is wrong query to fetch the desired output .

Next Updated Query be Chetan Suttraway :

explain analyze select distinct(p.crawled_page_id) from page_content p
 where NOT EXISTS (select 1 from  clause2 c where c.source_id = p.crawled_page_id);

                                                                    QUERY PLAN                                                                     
-----------------------------------------------------------------------------------------------------------------------------------------------------
 HashAggregate  (cost=100278.16..104104.75 rows=382659 width=8) (actual time=7192.843..7195.923 rows=72 loops=1)
   ->  Nested Loop Anti Join  (cost=0.00..99320.46 rows=383079 width=8) (actual time=0.040..7192.426 rows=74 loops=1)
         ->  Seq Scan on page_content p  (cost=0.00..87132.17 rows=428817 width=8) (actual time=0.009..395.599 rows=428467 loops=1)
         ->  Index Scan using idx_clause2_source_id on clause2 c  (cost=0.00..18.18 rows=781 width=4) (actual time=0.014..0.014 rows=1 loops=428467)
               Index Cond: (c.source_id = p.crawled_page_id)
 Total runtime: 7199.748 ms
(6 rows)

I think it is very much faster but I don't understand the query :

explain select distinct(b) from t1,t2 where t1.b >t2.d union all  select distinct(b) from t1,t2 where  t1.b <t2.d;

As i transform it into my format as:

explain select distinct(p.crawled_page_id) from page_content p , clause2 c where p.crawled_page_id > c.source_id union all  select distinct(p.crawled_page_id) from page_content p,clause2 c where p.crawled_page_id < c.source_id;

                                                     QUERY PLAN                                                     
---------------------------------------------------------------------------------------------------------------------
 Append  (cost=0.00..296085951076.34 rows=765318 width=8)
   ->  Unique  (cost=0.00..148042971711.58 rows=382659 width=8)
         ->  Nested Loop  (cost=0.00..136655213119.84 rows=4555103436696 width=8)
               ->  Index Scan using idx_page_id on page_content p  (cost=0.00..174214.02 rows=428817 width=8)
               ->  Index Scan using idx_clause2_source_id on clause2 c  (cost=0.00..185898.05 rows=10622488 width=4)
                     Index Cond: (p.crawled_page_id > c.source_id)
   ->  Unique  (cost=0.00..148042971711.58 rows=382659 width=8)
         ->  Nested Loop  (cost=0.00..136655213119.84 rows=4555103436696 width=8)
               ->  Index Scan using idx_page_id on page_content p  (cost=0.00..174214.02 rows=428817 width=8)
               ->  Index Scan using idx_clause2_source_id on clause2 c  (cost=0.00..185898.05 rows=10622488 width=4)
                     Index Cond: (p.crawled_page_id < c.source_id)
(11 rows)

I don't think this is correct because it produce 11 rows output.

Any further suggestions, Please guide.

Thanks & best Regards,
Adarsh Sharma