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Re: Why performance improvement on converting subselect to a function ?

From: Rajesh Kumar Mallah <mallah(at)trade-india(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Josh Berkus <josh(at)agliodbs(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org,"Shridhar Daithankar" <shridhar_daithankar(at)persistent(dot)co(dot)in>
Subject: Re: Why performance improvement on converting subselect to a function ?
Date: 2003-07-30 07:24:49
Message-ID: 200307301254.49159.mallah@trade-india.com (view raw or flat)
Thread:
Lists: pgsql-performance
Dear Tom,

the problem was repeatble in the sense repeated 
execution of queries made no difference on 
performance. 


What lead to degradation was the bumping off of
effective_cache_size parameter from 1000 to 64K

Can any one point me  the recent guide done by
Sridhar and Josh i want to see what i mis(read|understood)
 from  there ;-) [ it was on GeneralBits' Home Page ]

Anyway the performance gain was from 32 secs to less
than a sec what i restored cache size from 64K to 1000.

I will post again with more details but at the moment
i got to load my data_bank :)



Regds
Mallah.





On Wednesday 30 Jul 2003 3:02 am, Tom Lane wrote:
> Rajesh Kumar Mallah <mallah(at)trade-india(dot)com> writes:
> > Tom Lane wrote:
> >> Odd.  Apparently the planner is picking a better plan in the function
> >> context than in the subselect context --- which is strange since it
> >> ought to have less information.
> >
> > [ verbose plan snipped ]
>
> Well, that sure seems to be the same plan.  Curious that the runtime
> wasn't about the same.  Perhaps the slow execution of the first query
> was a caching effect?  If you alternate trying the query both ways,
> does the speed difference persist?
>
> 			regards, tom lane


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Subject: Re: Why performance improvement on converting subselect to a function ?
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Subject: Re: function returning setof performance question

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