Skip site navigation (1) Skip section navigation (2)

Re: simple join uses indexes, very slow

From: "Dave Dutcher" <dave(at)tridecap(dot)com>
To: "'Steinar H(dot) Gunderson'" <sgunderson(at)bigfoot(dot)com>,<pgsql-performance(at)postgresql(dot)org>
Subject: Re: simple join uses indexes, very slow
Date: 2006-03-29 01:30:23
Message-ID: 010a01c652d0$59ccd870$8300a8c0@tridecap.com (view raw or flat)
Thread:
Lists: pgsql-performance
> -----Original Message-----
> From: pgsql-performance-owner(at)postgresql(dot)org
[mailto:pgsql-performance-
> owner(at)postgresql(dot)org] On Behalf Of Steinar H. Gunderson
> A merge join requires sorted inputs.
> 
> > Most of the time was spent sorting the parameters parameters table
by
> > opset_num even though opset_num is indexed. Isn't Postgres able to
walk
> the
> > index instead of sorting?
> 
> The time of an index scan vs. a sequential scan + sort depends on
several
> factors, so it's not just a matter of walking the index whenever there
is
> one.

I was just looking this over again and I realized I misread the query
plan.  The slowest step was the Bitmap Heap Scan not the sort.  (The
sort was relatively fast.)




In response to

pgsql-performance by date

Next:From: Qingqing ZhouDate: 2006-03-29 04:59:34
Subject: Re: MVCC intro and benefits docs?
Previous:From: Jim C. NasbyDate: 2006-03-28 21:59:20
Subject: Re: MVCC intro and benefits docs?

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group