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, [EMAIL PROTECTED] 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/ ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
