Re: SLOW pG performance - Mailing list pgsql-novice

On Thu, 4 Sep 2003, Juan Francisco Diaz wrote:

> El 9/4/03 5:00 PM, "Stephan Szabo" <sszabo@megazone.bigpanda.com> escribi�:
>
> > On Thu, 4 Sep 2003, Juan Francisco Diaz wrote:
> >
> >> Hi again, I just tried the first load in my brand new pg database...
> >> And IT SUCKS! yeah! it took over an hour to load around 200 thousand
> >> records, while the sqlserver2000 took about 5-7 minutes...
> >> Im using the SAME program, some changes necessary but nothing really
> >> important.
> >
> > How were you loading the data, one row per transaction or batched in some
> > fashion?
> One row per transaction, in both cases sqlserver and pgsql.

There is a speed difference generally right now on loading single rows or
multiple rows in a transaction.  Batching is often preferred if possible.
:)

> > What do the schema(s) of the table(s) involved look like? What (if any)
> > constraints are involved (esp. foreign keys).
> There are 50 tables, but the ones were the insertion is taking place are
> only 10. Each of these 10 has one FK ((compoiste) and in a couple cases 2 FK
> (composite).
>
> The most used tables have more than 20 columns, and in two cases i have to
> break the insertion into two, an insertion and an update due to the large
> number of columns (39 and 45). Functions dont allow more than 32 parameters,
> anyone know why?

You can change it at compile time.  Raising it offers a small amount of
overhead currently and so it's not raised for the default install.

> I dont know if you would like to see ALL of the schemas, or if what ive told
> you is enough or if maybe you would like to see the schemas of the top 5
> tables.

One or two representative ones are probably fine.  It's a question of data
types (do all the foreign key constraints reference columns of the same
type for example) and indexes mostly.  Note my examples of things to look
for down below as well.

> > What do the specs of the relative machines look like?  Especially given
> > that in one case you're running multiple things on one machine and in the
> > other it sounds like they're on separate machines?
> >
> Yes sqlserver is in one server and locally im using postgresl.
> My local machine is a PowerPc G4 533Mhz with 256Megs in RAM, Mac OSX 10.2.6
> The DELL server, on which the sqlserver 2000 is running, is a P3 1.4gHz, 1
> gig RAM. (What a difference uh? I didnt realize the specs were so
> different... Until now)

That's a pretty big difference, especially the ram (especially since it
seems like it's also got apache and the client program running on it).
Another one might be related to the disk systems.

> > What do your function(s) look like?  Have you tried doing a subset not
> > using functions for comparison?
> >
> Ok, so im a newbie and i dont understand exactly the question, but the
> following is one of the most used functions (please tell me how and what is
> a subset and for what is it useful?):

I meant a subset of the inserts directly rather than through functions to
figure out if things were related to insert performance or the function
overhead.  See below for a comment on this particular function,
however.

> [function bits snipped]
> ����������������IF�CAST(Lista�AS�CHAR)�not�in�(select�IdLista�from�cabezalis
> ta�where�IdLista�=�CAST(Lista�AS�CHAR)�and�IdLibro�=�CAST(Libro�AS�CHAR(6)))
> [function bits snipped]

I'd suggest IF NOT EXISTS (select ...) since I believe that's equivalent
and possibly faster since you're already doing a comparison of
IdLista=CAST(Lista AS CHAR) in the subselect.  Also, for this particular
one, an index on (IdLista,IdLibro) may help the search (although it'd need
to be maintained by the insert, so it may be a wash), and you should
probably be careful with types here as well (and I'm not sure why you
aren't just declaring lista and libro as the appropriate types and not
casting them).