Re: [cx-oracle-users] Help with fetchraw

[Anthony T. <ant...@gm...>]

On 5/17/05, Chris Dunscombe <cdu...@ya...> wrote:
>=20
> --- Anthony Tuininga <ant...@gm...> wrote:
> > 2) I'm not sure exactly what you are intending with this so I can't
> > see why the simple
> >
> > for row in cursor:
> >     process_the_row()
> >
> > isn't going to work or isn't desirable. Perhaps you could give more
> > detail? Thanks.
>=20
> The "problem" with:
>=20
> for row in cursor:
>     process_the_row()
>=20
> is that process_the_row() is essentially:
>=20
> for col in row:
>     rowOut =3D rowOut.append(format_col(col))
> rowOutString =3D "".join(rowOut)
>=20
> which creates quite an overhead when the tables have lots of columns (>40=
).

You should be able to rewrite "process_the_row()" as the following if
all you are intending to do is replace None with ""

for row in cursor:
    rowOutString =3D "".join([v or "" for v in row])

if all you are fetching is strings. There is a flag for turning
numbers into strings in all cases as well. If you need something more
complicated than the above (multiple data types) then I'll need more
information. :-)

> So I'm looking at anything that could help speed things up (it's quite po=
ssible that in this case
> fetchraw() won't make much of an impact compared to the process_the_row()=
 code) This is why I'm
> looking the None as Null returning "" stuff so as to reduce the complexit=
y of "format_col()" and
> hence CPU cost.
>=20
> BTW I've actually put the process_the_row and format_col() code in-line a=
s per
> http://www.python.org/doc/faq/programming.html and associated performance=
 guidelines to avoid the
> function call overhead and this reduced the Python CPU usage by almost 20=
% on my standard perf
> test.
>=20
> Thanks again for your much appreciated help,

You're welcome. I hope to get the example of fetchraw() to you later
today but I expect to be interrupted shortly with a task that might
take all day so don't be alarmed if you don't hear from me right away.
I haven't forgotten about it. :-)

> Chris
> > On 5/12/05, Chris Dunscombe <cdu...@ya...> wrote:
> > > I'm looking to use cursor.fetchraw to help improve performance in an =
app I'm writing. I've
> > looked
> > > at CopyData from cx_OracleTools but I'm afraid I couldn't work it out=
.
> > > If possible I'd like a simple full example to show me the way. The co=
ntext is:
> > >
> > > 1) Retrieve rows from source table and insert into a target table whi=
ch has exactly the same
> > > structure.
> > >
> > > 2) Retrieve rows from source table, add some column formatting and wr=
ite out to a file.
> > >
> > > Thanks very much,
> > >
> > > Chris Dunscombe
> > >
> > > PS Thanks for all the input re my previous posting on Nulls and None.=
 I've still got some
> > thinking
> > > and work to do on which is best for performance and how best to cope =
with different datatypes,
> > > particularly Longs (what a pain they are!!)
> > >
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>=20
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