Re: [cx-oracle-users] AW: cx-oracle-users digest, Vol 1 #99 - 8 msgs

[D.R. B. <da...@as...>]

Hoi Chris,

Have you considered the following decorate/undecorate pattern?

   SQL:    SELECT strcolumn || 'x' FROM ...

   python: strcolumn =3D row[0][:-1]

As far as I can tell this will give about as much overhead as an if stateme=
nt.
However, only benchmarking your application will tell you what works best.

                                                   Danny


On Thu, May 12, 2005 at 01:22:56AM -0700, Chris Dunscombe wrote:
> Henning,
>=20
> I know what you mean, but the issue is that this "if test" has to go in s=
ome sort of function and
> be called for each col returned in each row and it's the function call ov=
erhead that's really the
> issue. I'd like to use the following:
>=20
> append =3D rowsOutput.append
> for row in data: # where data is the resultset from a query
>     rowsGroup =3D rowsGroup + 1
>     append("%s%s%s%s" %(row[0], colSep, row[1], colSep)) # In reality man=
y more columns
>     append(recSep)
>     if rowsGroup > :
>         outFile.write(''.join(rowsOutput))
>         rowsGroup =3D 0
>         rowsOutput =3D []
> outFile.write(''.join(rowsOutput))
>=20
> Now if I need to do the test on None then I believe I need to call a func=
tion or have the if test
> inline in a loop and with many columns this is quite an overhead. In my t=
est case on a 13 column
> table returning 200K rows:
>=20
> Doing the if test approx 20 CPU secs in Python
> No if test approx 16 CPU secs secs in Python
>=20
> A 20% reduction. I know the numbers here are small but given the app will=
 be running against many
> tables concurrently and extracting millions of rows the potential saving =
is significant.
>=20
> Thanks for taking the time to respond.
>=20
> Cheers,
>=20
> Chris
>=20
> --- Henning von Bargen <H.v...@t-...> wrote:
> > Chris,
> >=20
> > why do you think the simple statement "if x is None: x=3D''" means an
> > overhead?
> > It means about 0.000(insert zeroes here)1 percent performance overhead,
> > because transferring/outputting the data is what takes most of time.
> >=20
> > And - with Python - it should not mean too much typing overhead.
> > You could easily write a function to do this automatically for each
> > record.
> >=20
> > HTH
> > Henning
> >=20
> >=20
> > > -----Urspr?ngliche Nachricht-----
> > > From: Chris Dunscombe <cdu...@ya...>
> > > To: cx-oracle-list <cx-...@li...>
> > > Subject: [cx-oracle-users] Nulls returned as None and not as=20
> > > as "empty or zero lenght string"
> > > Reply-To: cx-...@li...
> > >=20
> > > All,
> > >=20
> > > Is there anyway that Null values returned from a query can be=20
> > > an "empty or zero length string"
> > > instead of None?
> > >=20
> > > This may seem a strange request as it's easy to use type to=20
> > > test if a null has been returned as
> > > None. However I've a performance critical app where I need to=20
> > > output "nothing" (zero length /
> > > empty string) if the value is null. Hence at present I have=20
> > > to perform this "type test" on ALL
> > > columns that don't have a "Not Null" constraint in the=20
> > > database which is quite an overhead when in
> > > some cases I need to do it millions and sometimes billions of times.
> > >=20
> > > Thanks,
> > >=20
> > > Chris Dunscombe
> > >=20
> >=20
> >=20
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>=20
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