Re: Perl DBI, PostgreSQL performance question - Mailing list pgsql-general

Perl is an interpreted language. It does not convert into byte code.

It is scanned each time you can it so the interpreter has to go through
everything line by line. There is no template that is run such as when you
write a plpgsql function

Hope this helps

Darren

Darren Ferguson
Software Engineer
Openband

On Fri, 14 Dec 2001, Frank Finner wrote:

> Hi,
>
> a Perl compiler optimizes. Does anybody know what really happens while
> it optimizes? I think, both parts may be optimized (nearly) the same
> way. so the resulting bytecode might be rather the same...
>
> Correct me, if I am wrong.
>
> mfg Frank Finner
>
> On 14-Dec-01 Benjamin Franks sat down, thought for a long time and then
> wrote:
> > I'm using the Perl DBI to interact with my PostgreSQL 7.1.3 database.
> > I had a section of code that looked something like the
> > following (it's only pseudocode):
> >
> > **************
> > foreach
> >       foreach
> >               eval {
> >                       prepare first select statement;
> >                       execute first select;
> >                       prepare first update or insert;
> >                       execute first update or insert;
> >
> >                       prepare second select statement;
> >                       execute second select;
> >                       prepare second update or insert;
> >                       execute second update or insert;
> >
> >                       commit;
> >               };
> >               if ($@) {
> >                       rollback;
> >               }
> >       }
> > }
> > ***************
> >
> > I realized some of those statements did not need to be inside the
> > loops
> > and so figure if I changed the code to the following, it would speed
> > up:
> >
> > ***************
> > prepare first select statement;
> > prepare first update;
> > prepare first insert;
> > foreach
> >       eval {
> >               execute first select statement;
> >               execute first update or insert;
> >               commit;
> >       };
> >       if ($@) {
> >               rollback;
> >               next;
> >       }
> >
> >       prepare second select statement;
> >       prepare second update;
> >       prepare second insert;
> >
> >       foreach
> >               eval {
> >                       execute second select;
> >                       execute second update or insert;
> >                       commit;
> >               };
> >               if ($@) {
> >                       rollback;
> >               }
> >       }
> > }
> > ***************
> >
> > The results are the same in the database either way. From what I can
> > tell, it did not speed up.  In fact it actually slowed
> > down.  The SQL statements haven't changed at all and I haven't
> > changed the database schema, version, configuration options,
> > etc..  I would have imagined the second sequence would have been much
> > faster because needless SQL isn't being done inside the
> > inner loops.  Does anyone have any ideas as to why this would be the
> > case?  Could it have to do with moving from a single eval
> > block to two eval blocks with some statements outside the eval?  What
> > about multiple commits--could they be expensive
> > operations?
> >
> > I appreciate any info you may be able to provide.
> > Thanks,
> > --Ben
> >
> > ----------------------------------------------------------------------
> > ---
> > "From causes which appear similar, we expect similar effects.  This
> > is the
> >  sum total of all our experimental conclusions." --David Hume
> >
> >
> >
> > ---------------------------(end of
> > broadcast)---------------------------
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> >
> > http://www.postgresql.org/users-lounge/docs/faq.html
>
> --
> Frank Finner
>
> And now there is no turning back at all.
>                               (M. Moorcock, "Elric Of Melnibone")"
>
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>