Re: UPDATEDs slowing SELECTs in a fully cached database

From: Ivan Voras
Subject: Re: UPDATEDs slowing SELECTs in a fully cached database
Date: ,
Msg-id: ivhhr6$rin$1@dough.gmane.org
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In response to: UPDATEDs slowing SELECTs in a fully cached database  (lars)
Responses: Re: UPDATEDs slowing SELECTs in a fully cached database  (Merlin Moncure)
List: pgsql-performance

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UPDATEDs slowing SELECTs in a fully cached database  (lars, )
 Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
  Re: UPDATEDs slowing SELECTs in a fully cached database  (Craig Ringer, )
   Re: UPDATEDs slowing SELECTs in a fully cached database  (lars hofhansl, )
    Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
     Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
      Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
       Re: UPDATEDs slowing SELECTs in a fully cached database  (Merlin Moncure, )
        Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
         Re: UPDATEDs slowing SELECTs in a fully cached database  (Merlin Moncure, )
        Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
         Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
          Re: UPDATEDs slowing SELECTs in a fully cached database  (Ivan Voras, )
           Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
            Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
             Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
              Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
              Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
               Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
                Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
               Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
                Re: UPDATEDs slowing SELECTs in a fully cached database  (Tom Lane, )
                 Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
                  Re: UPDATEDs slowing SELECTs in a fully cached database  (Merlin Moncure, )
                  Re: UPDATEDs slowing SELECTs in a fully cached database  (Jeff Janes, )
                 Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
                  Re: UPDATEDs slowing SELECTs in a fully cached database  (Tom Lane, )
                   Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
                    Re: UPDATEDs slowing SELECTs in a fully cached database  (Robert Klemme, )
                    Re: UPDATEDs slowing SELECTs in a fully cached database  (Tom Lane, )
                     Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
                Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
                 Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
                  Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
                   Re: UPDATEDs slowing SELECTs in a fully cached database  (Jeff Janes, )
                    Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
                     Re: UPDATEDs slowing SELECTs in a fully cached database  (Jeff Janes, )
                      Re: UPDATEDs slowing SELECTs in a fully cached database  (Greg Smith, )
              Re: UPDATEDs slowing SELECTs in a fully cached database  (Jeff Janes, )
               Re: UPDATEDs slowing SELECTs in a fully cached database  (Tom Lane, )
             Re: UPDATEDs slowing SELECTs in a fully cached database  (Merlin Moncure, )
              Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
               Re: UPDATEDs slowing SELECTs in a fully cached database  (Merlin Moncure, )
                Re: UPDATEDs slowing SELECTs in a fully cached database  (Pavan Deolasee, )
                 Re: UPDATEDs slowing SELECTs in a fully cached database  (lars hofhansl, )
                  Re: UPDATEDs slowing SELECTs in a fully cached database  (Jeff Janes, )
            Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
 Re: UPDATEDs slowing SELECTs in a fully cached database  ("", )
  Re: UPDATEDs slowing SELECTs in a fully cached database  (Robert Klemme, )
   Re: UPDATEDs slowing SELECTs in a fully cached database  ("", )
   Re: UPDATEDs slowing SELECTs in a fully cached database  (lars, )
    Re: UPDATEDs slowing SELECTs in a fully cached database  ("Kevin Grittner", )
     Re: UPDATEDs slowing SELECTs in a fully cached database  (Merlin Moncure, )
 Re: UPDATEDs slowing SELECTs in a fully cached database  (Ivan Voras, )
  Re: UPDATEDs slowing SELECTs in a fully cached database  (Merlin Moncure, )
   Re: UPDATEDs slowing SELECTs in a fully cached database  (Ivan Voras, )
 Re: UPDATEDs slowing SELECTs in a fully cached database  (Lars, )

On 08/07/2011 01:56, lars wrote:

> Setup:
> PostgreSQL 9.1beta2 on a high memory (~68gb, 12 cores) EC2 Linux
> instance (kernel 2.6.35) with the database and
> WAL residing on the same EBS volume with EXT4 (data=ordered, barriers=1)
> - yes that is not an ideal setup
> (WAL should be on separate drive, EBS is slow to begin, etc), but I am
> mostly interested in read performance for a fully cached database.

I know you said you know these things - but do you really know the
(huge) extent to which all your IO is slowed? Even context switches in a
virtualized environment are slowed down by a huge margin - which would
make practically all in-memory lock operations very slow - much slower
than they would be on "real" hardware, and EBS by definition is even
slower then regular private virtual storage environments. I regrettably
didn't bookmark the page which did exact measurements of EBS, but
http://www.google.com/search?q=how+slow+is+ec2 will illustrate my point.
(of course, you may already know all this :) ).



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From: "Kevin Grittner"
Date:
Subject: Re: UPDATEDs slowing SELECTs in a fully cached database
From: "Kevin Grittner"
Date:
Subject: Re: UPDATEDs slowing SELECTs in a fully cached database