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Re: migrating oracle to postgres

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On 06/23/2011 06:42 PM, Mladen Gogala wrote:
> On Thu, 23 Jun 2011 17:48:09 +0200, Robert Klemme wrote:
>
>> Why do you consider this bad?  I agree that it sounds silly at first
>> sight that the user needs to take care of cleaning up deadwood in the
>> database.  On the other hand, on an Oracle instance you'll likely also
>> have periodic jobs doing statistics updates which is what VACUUMing also
>> does.  Reducing the work a transaction has to do can be beneficial for
>> the client, too.
>
> No, what I consider bad is the architecture of putting dead rows in the
> table. That prevents Postgres from assigning a fixed row id to every row
> and from creating global indexes on partitioned tables. I believe that
> they should consider putting previous versions of the row in a separate
> table and have the vacuum process, let's call it "smon" for the sake of
> argument, do a periodical cleanup. That way rows in the table are not a
> moving target, there is a possibility of assigning a permanent row id,
> which would also allow creating global indexes.

Aha, thanks for clarifying!  I think I need to read up a bit on 
PostgreSQL architecture.  Generally both approaches (copy on write, 
backup old version) work and PostgreSQL simply did choose another way to 
do it than Oracle.  I am not sure yet which one is better.  When I think 
about infamous ORA-01555 I would at least say that Oracle's approach has 
caused its share of grief for DB users. :-)  Which approach is best 
certainly depends on usage patterns (how much concurrency, ratio of read 
to write activity, inserts vs. deletes vs. updates etc.).

>>> The third is the fact that Postgres doesn't do multi-block reads.
>>
>> Isn't this alleviated by the OS doing readahead on many platforms?
>
> Weeellllll....it is. You are right, my objection is mostly of aesthetic
> nature. When I come to think of it, it does simplify the optimizer
> because there is only one type of I/O to think about.

:-)

>>> Fixed size archive logs (16M) would be the next issue.
>>
>> This can be changed during compilation though.  But I agree, you'd
>> rather want this to be tuneable at runtime - at least without
>> recompiling the software.
>>
>>> The lack of shared pool makes it impossible to see the plan of the
>>> statement being executed. And there is more.
>>
>> That's unfortunate.  At least you can see SQL currently executed by
>> querying pg_stat_activity.
>
> Oh yes, and there is also auto explain module which will dump the plan of
> any statement running longer than a predefined period of time (tunable).
> What I really miss is the ability to click on the session in PgAdmin3 and
> see the plan of a running statement. Also, sorting by the CPU time or the
> number of I/O requests issued would be nice.

So it's rather an issue of the administration UI and not of the database 
itself.  It wasn't that long ago that even Oracle did not have a 
graphical UI for administration - IIRC it was Oracle 10 which packaged 
Enterprise Manager with the DB by default the first time.  At that time 
I still considered Microsoft SQL Server's tools better.

Kind regards

	robert

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migrating oracle to postgres Username <user@domain.tld> - 2011-06-20 19:28 +0200
  Re: migrating oracle to postgres Mladen Gogala <no@email.here.invalid> - 2011-06-20 20:08 +0000
    Re: migrating oracle to postgres Username <user@domain.tld> - 2011-06-20 23:45 +0200
      Re: migrating oracle to postgres Mladen Gogala <no@email.here.invalid> - 2011-06-20 22:37 +0000
      Re: migrating oracle to postgres Mladen Gogala <gogala.mladen@gmail.com> - 2011-06-21 02:01 +0000
  Re: migrating oracle to postgres "Laurenz Albe" <invite@spam.to.invalid> - 2011-06-21 09:18 +0200
    Re: migrating oracle to postgres Mladen Gogala <gogala.mladen@gmail.com> - 2011-06-21 13:38 +0000
      Is PostgreSQL good? (was: migrating oracle to postgres) "Laurenz Albe" <invite@spam.to.invalid> - 2011-06-22 12:30 +0200
        Re: Is PostgreSQL good? Harry Tuttle <OTPXDAJCSJVU@spammotel.com> - 2011-06-22 13:15 +0200
        Re: Is PostgreSQL good? (was: migrating oracle to postgres) Mladen Gogala <gogala.mladen@gmail.com> - 2011-06-22 12:02 +0000
          Re: Is PostgreSQL good? "M. Strobel" <sorry_no_mail_here@nowhere.dee> - 2011-06-22 21:52 +0200
            Re: Is PostgreSQL good? Mladen Gogala <no@email.here.invalid> - 2011-06-22 22:43 +0000
          Re: Is PostgreSQL good? (was: migrating oracle to postgres) "Laurenz Albe" <invite@spam.to.invalid> - 2011-06-24 12:29 +0200
            Re: Is PostgreSQL good? Hans Castorp <REWYRLXHEGHO@spammotel.com> - 2011-06-24 12:57 +0200
              Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-06-24 14:53 +0200
              Re: Is PostgreSQL good? Mladen Gogala <no@email.here.invalid> - 2011-06-24 16:32 +0000
            Re: Is PostgreSQL good? (was: migrating oracle to postgres) Mladen Gogala <gogala.mladen@gmail.com> - 2011-06-24 13:53 +0000
              Re: Is PostgreSQL good? (was: migrating oracle to postgres) "Laurenz Albe" <invite@spam.to.invalid> - 2011-06-27 11:17 +0200
                Re: Is PostgreSQL good? (was: migrating oracle to postgres) Mladen Gogala <gogala.mladen@gmail.com> - 2011-06-28 06:11 +0000
                Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-06-28 10:34 +0200
                Re: Is PostgreSQL good? Mladen Gogala <gogala.mladen@gmail.com> - 2011-06-28 13:30 +0000
                Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-06-29 09:50 +0200
                Re: Is PostgreSQL good? Mladen Gogala <no@email.here.invalid> - 2011-06-29 21:38 +0000
                Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-06-30 09:14 +0200
                Re: Is PostgreSQL good? Mladen Gogala <mgogala@no.address.invalid> - 2011-06-30 13:22 +0000
            Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-06-30 07:05 -0700
              Re: Is PostgreSQL good? Mladen Gogala <no@email.here.invalid> - 2011-06-30 15:41 +0000
                Re: Is PostgreSQL good? Richard Kettlewell <rjk@greenend.org.uk> - 2011-06-30 16:49 +0100
                Re: Is PostgreSQL good? Mladen Gogala <no@email.here.invalid> - 2011-06-30 19:24 +0000
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-06-30 13:21 -0700
                Re: Is PostgreSQL good? Mladen Gogala <no@email.here.invalid> - 2011-06-30 22:42 +0000
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-07-01 11:57 -0700
                Re: Is PostgreSQL good? Mladen Gogala <gogala.mladen@gmail.com> - 2011-07-01 22:58 +0000
                Re: Is PostgreSQL good? Richard Kettlewell <rjk@greenend.org.uk> - 2011-07-01 14:07 +0100
                Re: Is PostgreSQL good? Mladen Gogala <gogala.mladen@gmail.com> - 2011-07-01 13:29 +0000
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-06-30 13:17 -0700
                Re: Is PostgreSQL good? Mladen Gogala <gogala.mladen@gmail.com> - 2011-06-30 23:53 +0000
              Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-07-01 10:13 +0200
                Re: Is PostgreSQL good? Mladen Gogala <gogala.mladen@gmail.com> - 2011-07-01 13:38 +0000
                Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-07-01 16:58 +0200
                Re: Is PostgreSQL good? Mladen Gogala <no@email.here.invalid> - 2011-07-01 15:33 +0000
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-07-01 11:39 -0700
                Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-07-04 16:39 +0200
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-07-04 12:11 -0700
                Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-07-05 08:58 +0200
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-07-05 11:29 -0700
                Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-07-06 09:00 +0200
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-07-06 01:00 -0700
                Re: Is PostgreSQL good? "Laurenz Albe" <invite@spam.to.invalid> - 2011-07-07 09:05 +0200
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-07-07 00:34 -0700
                Re: Is PostgreSQL good? Matthew Woodcraft <mattheww@chiark.greenend.org.uk> - 2011-07-04 20:12 +0100
                Re: Is PostgreSQL good? Don Y <nowhere@here.com> - 2011-07-04 12:24 -0700
      Re: migrating oracle to postgres Robert Klemme <shortcutter@googlemail.com> - 2011-06-23 17:48 +0200
        Re: migrating oracle to postgres Mladen Gogala <no@email.here.invalid> - 2011-06-23 16:42 +0000
          Re: migrating oracle to postgres Mladen Gogala <no@email.here.invalid> - 2011-06-23 18:57 +0000
          Re: migrating oracle to postgres Robert Klemme <shortcutter@googlemail.com> - 2011-06-26 17:35 +0200
            Re: migrating oracle to postgres Mladen Gogala <gogala.mladen@gmail.com> - 2011-06-26 19:08 +0000
          Re: migrating oracle to postgres Robert Klemme <shortcutter@googlemail.com> - 2011-06-27 00:32 -0700
            Re: migrating oracle to postgres Mladen Gogala <no@email.here.invalid> - 2011-06-28 16:00 +0000
              Re: migrating oracle to postgres Robert Klemme <shortcutter@googlemail.com> - 2011-06-28 22:28 +0200

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