Re: Delete query takes exorbitant amount of time

From: Karim A Nassar
Subject: Re: Delete query takes exorbitant amount of time
Date: ,
Msg-id: Pine.SOL.4.21.0503281231580.1035-100000@coruscant.cet.nau.edu
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In response to: Re: Delete query takes exorbitant amount of time  (Simon Riggs)
List: pgsql-performance

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Delete query takes exorbitant amount of time  (Karim Nassar, )
 Re: Delete query takes exorbitant amount of time  (Tom Lane, )
  Re: Delete query takes exorbitant amount of time  (Mark Lewis, )
   Re: Delete query takes exorbitant amount of time  (Tom Lane, )
    Re: Delete query takes exorbitant amount of time  (Christopher Kings-Lynne, )
    Re: Delete query takes exorbitant amount of time  (Oleg Bartunov, )
    Re: Delete query takes exorbitant amount of time  (Mark Lewis, )
     Re: Delete query takes exorbitant amount of time  (Gaetano Mendola, )
   Re: Delete query takes exorbitant amount of time  (Christopher Kings-Lynne, )
  Re: Delete query takes exorbitant amount of time  (Karim Nassar, )
   Re: Delete query takes exorbitant amount of time  (Josh Berkus, )
    Re: Delete query takes exorbitant amount of time  (Karim Nassar, )
 Re: Delete query takes exorbitant amount of time  (Tom Lane, )
  Re: Delete query takes exorbitant amount of time  (Christopher Kings-Lynne, )
   Re: Delete query takes exorbitant amount of time  (Vivek Khera, )
   Re: Delete query takes exorbitant amount of time  (Tom Lane, )
    Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
     Re: Delete query takes exorbitant amount of time  (Tom Lane, )
      Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
       Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
        Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
         Re: Delete query takes exorbitant amount of time  (Tom Lane, )
          Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
           Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
            Re: Delete query takes exorbitant amount of time  (Tom Lane, )
             Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
         Re: Delete query takes exorbitant amount of time  (Christopher Kings-Lynne, )
     Re: Delete query takes exorbitant amount of time  (Karim Nassar, )
      Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
       Re: Delete query takes exorbitant amount of time  (Karim Nassar, )
        Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
         Re: Delete query takes exorbitant amount of time  (Karim Nassar, )
          Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
           Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
  Re: Delete query takes exorbitant amount of time  (Karim Nassar, )
 Re: Delete query takes exorbitant amount of time  (Tom Lane, )
 Re: Delete query takes exorbitant amount of time  (Josh Berkus, )
  Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
 Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
  Re: Delete query takes exorbitant amount of time  (Karim A Nassar, )
 Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
  Re: Delete query takes exorbitant amount of time  (Karim A Nassar, )
 Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
  Re: Delete query takes exorbitant amount of time  (Karim A Nassar, )
   Re: Delete query takes exorbitant amount of time  (Bruno Wolff III, )
 Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
  Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
   Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
    Re: Delete query takes exorbitant amount of time  (Tom Lane, )
     Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
      Re: Delete query takes exorbitant amount of time  (Tom Lane, )
       Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
        Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
     Re: Delete query takes exorbitant amount of time  (Stephan Szabo, )
   Re: Delete query takes exorbitant amount of time  (Tom Lane, )
   Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
  Re: Delete query takes exorbitant amount of time  (Tom Lane, )
   Re: Delete query takes exorbitant amount of time  (Simon Riggs, )
    Re: Delete query takes exorbitant amount of time  (Tom Lane, )
     Re: Delete query takes exorbitant amount of time  (Simon Riggs, )

> Well, based upon the evidence so far, the Optimizer got it right:

Agreed. So, this means that the answer to my original question is "that
delete gonna take a long time"?

Seems that there is still something wrong. From what I can tell from
everyones questions, the FK constraint on measurement is causing multiple
seq scans for each value deleted from int_sensor_meas_type. However, when
deleting a single value, the FK check should use the index, so my ~190
deletes *should* be fast, no?

> IndexScan, value=1    elapsed= 29ms    cost=883881

190 * 29ms is much less than 40 minutes. What am I missing here?


> Karim,
> Please do:
>
> select id_int_sensor_meas_type, count(*)
> from measurement
> group by id_int_sensor_meas_type
> order by count(*) desc;

id_int_sensor_meas_type | count
-------------------------+--------
                      31 | 509478
                      30 | 509478
                     206 | 509478
                     205 | 509478
                     204 | 509478
                      40 | 509478
                      39 | 509478
                     197 | 509478
                      35 | 509478
                      34 | 509478
                      33 | 509478
                      32 | 509478
                      41 | 509477

This sample dataset has 13 measurements from a weather station over 3
years, hence the even distribution.


Continued thanks,
--
Karim Nassar
Department of Computer Science
Box 15600, College of Engineering and Natural Sciences
Northern Arizona University,  Flagstaff, Arizona 86011
Office: (928) 523-5868 -=- Mobile: (928) 699-9221






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