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Re: Is PostgreSQL good?

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Hi Laurenz, (et al.)

[apologies for not having the technical depth to understand these
issues better -- I just use PostgreSQL as a "means to an end"...
I could use any similar "means" but this seems to work well enough
for me]

I write a lot of code (in C, etc.) and *deliberately* let the compiler
do as much work as possible, for me -- concentrating on picking good
*algorithms* instead of micromanaging individual lines of code.  If
performance is a *real* issue (like processing video frames in
real-time) and I *can't* change the hardware (because this isn't
a handful of servers, but, rather, thousands of "retail devices"),
then I will drop into assembly language to code *very tiny* portions
of the algorithm where the gains are the most substantial.  I.e.,
my philosophy is to let the machine do the thinking/work, wherever
possible.

Can someone please, *gently*, explain *quantitatively* the differences
that these issues make in performance?

(see below)

On 6/24/2011 3:29 AM, Laurenz Albe wrote:

> About hints:
> ============
>
> Let me say that I personally do not feel very strongly
> either way - I have used hints in Oracle and get by without them in PostgreSQL.

Are hints on a par with the 'register' keyword in C?  I.e.,
something you *hope* gives the compiler an insight into your
algorithm -- but, that the compiler is free to *ignore*?
Are there consequences to using a "hint" (e.g., using 'register'
places constraints on what you can do)?

Is the "hint" concept essentially a workaround to compensate for
capabilities *missing* in the optimizer?  I.e., as C compilers
get smarter, they deliberately *choose* to ignore the 'register'
keyword because they actually have *more* insight than the
programmer!

Are there ways (without using a "hint") to coerce the database
to perform in the way your hint would *hope* to have it behave?
(e.g., can you rewrite the SQL to cause the behavior you seek?)

[these all seem to be parallels to the register/compiler
example I posed]

What sort of *quantitative* difference can this make (example?)
that can't, otherwise, be attained?

> About vacuum:
> =============
>
> Of course vacuum is a pain, but every database system has to pay a similar
> price somewhere. Either you reduce concurrency (DB2), or (if you use some kind
> of MVCC) you can move dead rows somewhere else (Oracle) or leave them where
> they are and clean up later.

Is this just the difference between automatic garbage collection
and "manual" garbage collection (again, relying on parallels to
other "languages")?

Does the parallel maintain throughout operation or does it fall
apart at the extremes?  E.g., if garbage collection must be
manually initiated (in a language), then failing to do so
can eventually cause you to run out of heap, etc. (which
causes the application to "fail").  Is the same true when
it comes to vacuuming -- or, does performance just suffer?
(i.e., will you ever "fill the disk" with dead rows if you
fail to initiate a VACUUM operation?)

> ROWID:
> ======
>
> You make the point that because of VACUUM there is nothing compared to
> Oracle's ROWID. But do you really need that? Shouldn't a row be referenced
> by its primary key?

The last question seems to be my understanding of how things should
work. (?)  (actually, one of the harder ideas for me to get accustomed
to in this field  :< )

How does a ROWID differ from using an OID?  (which I presume is
not a good thing)

> Fixed size of WAL segments:
> ===========================
>
> Maybe I am dense, but what is the problem there?

<grin>  I don't even know what they *are*!  ;-)

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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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