Hi all;
I have a simple query against two very large tables ( > 800million rows in
theurl_hits_category_jt table and 9.2 million in the url_hits_klk1 table )
I have indexes on the join columns and I've run an explain.
also I've set the default statistics to 250 for both join columns. I get a
very high overall query cost:
explain
select
category_id,
url_hits_id
from
url_hits_klk1 a ,
pwreport.url_hits_category_jt b
where
a.id = b.url_hits_id
;
QUERY PLAN
--------------------------------------------------------------------------------------------
Hash Join (cost=296959.90..126526916.55 rows=441764338 width=8)
Hash Cond: (b.url_hits_id = a.id)
-> Seq Scan on url_hits_category_jt b (cost=0.00..62365120.22
rows=4323432222 width=8)
-> Hash (cost=179805.51..179805.51 rows=9372351 width=4)
-> Seq Scan on url_hits_klk1 a (cost=0.00..179805.51 rows=9372351
width=4)
(5 rows)
If I turn off sequential scans I still get an even higher query cost:
set enable_seqscan = off;
SET
explain
select
category_id,
url_hits_id
from
url_hits_klk1 a ,
pwreport.url_hits_category_jt b
where
a.id = b.url_hits_id
;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------
Merge Join (cost=127548504.83..133214707.19 rows=441791932 width=8)
Merge Cond: (a.id = b.url_hits_id)
-> Index Scan using klk1 on url_hits_klk1 a (cost=0.00..303773.29
rows=9372351 width=4)
-> Index Scan using mt_url_hits_category_jt_url_hits_id_index on
url_hits_category_jt b (cost=0.00..125058243.39 rows=4323702284 width=8)
(4 rows)
Thoughts?
Thanks in advance
