Re: Query not using Index

Hi Andreas,

The tablespace is not on SSD although I intend to do it within the next
week. I actually tried reducing the random_page_cost to 0.2 but it doesn't
help.

On 26 March 2016 at 22:13, Andreas Kretschmer <akretschmer(at)spamfence(dot)net>
wrote:

> Wei Shan <weishan(dot)ang(at)gmail(dot)com> wrote:
>
> > Hi all,
> >
> > Please provide some advise on the following query not using the index:
> > I have 2 questions:
> >
> > 1. Why does the optimizer chose not to use the index when it will run
> faster?
>
> because of the estimated costs.:
>
> Seq Scan on testdb auditrecor0_ (cost=0.00..18147465.00
> Bitmap Heap Scan on testdb auditrecor0_ (cost=2291521.32..19046381.97
>
> The estimated costs for the index-scan are higher.
>
>
> > 2. How do I ensure the optimizer will use the index without setting
> > enable_seqscan='off'
>
> You have a dedicated tablespace for indexes, is this a SSD? You can try
> to reduce the random_page_cost, from default 4 to maybe 2.(depends on
> hardware) This would reduce the estimated costs for the Index-scan and
> prefer the index-scan.
>
>
>
> Regards, Andreas Kretschmer
> --
> Andreas Kretschmer
> http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>
>
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--
Regards,
Ang Wei Shan