Re: [pgsql-performance] Is dump-reload the only cure?

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



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