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Re: Query much faster with enable_seqscan=0

From: Ogden <lists(at)darkstatic(dot)com>
To: Greg Smith <greg(at)2ndquadrant(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Query much faster with enable_seqscan=0
Date: 2010-09-21 19:34:42
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Sep 21, 2010, at 2:16 PM, Greg Smith wrote:

> Joshua D. Drake wrote:
>> PostgreSQL's defaults are based on extremely small and some would say
>> (non production) size databases. As a matter of course I always
>> recommend bringing seq_page_cost and random_page_cost more in line.
> Also, they presume that not all of your data is going to be in memory, and the query optimizer needs to be careful about what it does and doesn't pull from disk.  If that's not the case, like here where there's 8GB of RAM and a 7GB database, dramatic reductions to both seq_page_cost and random_page_cost can make sense.  Don't be afraid to think lowering below 1.0 is going too far--something more like 0.01 for sequential and 0.02 for random may actually reflect reality here.

I have done just that, per your recommendations and now what took 14 seconds, only takes less than a second, so it was certainly these figures I messed around with. I have set:

seq_page_cost = 0.01           
random_page_cost = 0.02   
cpu_tuple_cost = 0.01

Everything seems to run faster now. I think this should be fine - I'll keep an eye on things over the next few days. 

I truly appreciate everyone's help. 


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