Hi Rod ,
Does it means that index scan is used for less frequenlty occuring data?
yes my table was not clustered.
can u tell me what does 0.00..6788.24 and rows and width means?
in explain out put cost=0.00..6788.24 rows=30001 width=4
I have one more table where i face the similar problem , i have not dump - reloaded
it yet , will post again if i face the problem.
thanks
Regds
Mallah.
> On Fri, 2002-11-01 at 06:15, mallah@trade-india.com wrote:
>
>
> Looks like a borderline case. See the costs of the index scan and sequential scan are very
> similar. Since 499 covers nearly 1 in 10 tuples, it's likely found on nearly every page. This
> should make a sequential scan much cheaper.
>
> However, if the data is clumped together (not distributed throughout the table) than an index
> scan may be preferable. So... CLUSTER may be useful to you.
>
> In the future please 'explain analyze' the queries you're looking at to see actual costs as
> compared to the estimated cost.
>
>
>> 499 | 25010
>> 501 | 3318
>>
>>
>> before dump reload:
>> tradein_clients=# VACUUM VERBOSE ANALYZE email_bank_mailing_lists; NOTICE: --Relation
>> email_bank_mailing_lists--
>> NOTICE: Pages 3583: Changed 0, Empty 0; Tup 256419: Vac 0, Keep 0, UnUsed 44822.
>> Total CPU 0.24s/0.04u sec elapsed 0.30 sec.
>> NOTICE: Analyzing email_bank_mailing_lists
>> VACUUM
>> tradein_clients=# explain SELECT count( email_id ) from email_bank_mailing_lists where
>> query_id=499;NOTICE: QUERY PLAN:
>>
>> Aggregate (cost=6863.24..6863.24 rows=1 width=4)
>> -> Seq Scan on email_bank_mailing_lists (cost=0.00..6788.24 rows=30001 width=4)
>>
>> EXPLAIN
>
> --
> Rod Taylor
-----------------------------------------
Get your free web based email at trade-india.com.
"India's Leading B2B eMarketplace.!"
http://www.trade-india.com/
