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Re: Querying 19million records very slowly

From: Kjell Tore Fossbakk <kjelltore(at)gmail(dot)com>
To: Michael Glaesemann <grzm(at)myrealbox(dot)com>
Cc: Tobias Brox <tobias(at)nordicbet(dot)com>,pgsql-performance(at)postgresql(dot)org
Subject: Re: Querying 19million records very slowly
Date: 2005-06-22 09:10:42
Message-ID: e79986c50506220210578776e@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
> Try to type in '2005-06-21 16:36:22+08' directly in the query, and see if it
> makes changes.  Or probably '2005-06-21 10:36:22+02' in your case ;-)

Which one does Pg read fastes? Does he convert datetime in the table,
then my where clause and check, for each row? How does he compare a
datetime with a datetime? Timestamp are easy, large number bigger than
another large number..

time (datetime) > '2005-06-21 10:36:22+02'

or 

time (timestamp) > 'some timestamp pointing to yesterday'

Hmm.. I cant find any doc that describes this very good.


On 6/22/05, Michael Glaesemann <grzm(at)myrealbox(dot)com> wrote:
> 
> On Jun 22, 2005, at 5:39 PM, Tobias Brox wrote:
> 
> > (btw, does postgresql really handles timezones?  '+02' is quite  
> > different
> > from 'CET', which will be obvious sometime in the late autoumn...)
> 
> Yes, it does. It doesn't (currently) record the time zone name, but  
> rather only the offset from UTC. If a time zone name (rather than UTC  
> offset) is given, it is converted to the UTC offset *at that  
> timestamptz* when it is stored. For time zones that take into account  
> DST, their UTC offset changes during the year, and PostgreSQL records  
> the equivalent UTC offset for the appropriate timestamptz values.
> 
> There has been discussion in the past on storing the time zone name  
> with the timestamptz as well, though no one has implemented this yet.
> 
> Michael Glaesemann
> grzm myrealbox com
> 
> 
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